sunscreen science experiment hypothesis

Science in School

How effective is your sunscreen teach article.

Author(s): Fina Guitart, Silvia Lope

Encourage students to stay safe in the sun with a collection of activities to discover the science behind sunscreen.

Whether it’s enjoying a summer’s day on the beach, skiing down the slopes in winter, or simply going outside for some fresh air during a lunch break, any time spent outdoors leaves our skin vulnerable to the Sun’s ultraviolet (UV) rays. Applying sunscreen is key to protecting ourselves from the damaging effects of sunlight, but have you ever stopped to consider how your sunscreen works – and ultimately, how effective it is?

To find out, we devised the following activities for students aged 14–17 to explore the science behind sunscreen and to investigate its effectiveness for UV protection. In the process, students will appreciate the importance of protecting themselves from sunlight, and will be more able to make informed decisions regarding their use of sunscreens. We recommend that students work in small groups (e.g. 2–3 students per group) throughout.

Activity 1: An introduction to UV protection

This activity introduces students to the key ingredients in sunscreens, and explores the difference between organic and inorganic UV filters. In small groups, students study the labels of various store-bought sunscreens to determine the key ingredients and types of UV filters that are commonly used. We recommend placing the sunscreen bottles around the classroom, with each group working their way around the different sunscreen products. You could collect your own selection of sunscreen products, or ask your students to bring in products from home. This activity (including a class discussion) takes approximately 50 minutes, and it is helpful to complete it before the main activities.

To have a diverse collection of sunscreens, try and find the following:

• One sunscreen with low protection (SPF 15 or below)
• One sunscreen with medium–high protection (SPF 30–50)
• One sunscreen with very high protection (SPF 50+)
• One sunscreen formulated for babies/children
• One sunscreen for water sports (high water-resistance)
• One sunscreen with titanium dioxide or zinc oxide (inorganic active ingredients)

Ask your students to work through the following steps:

• In your group, begin by examining the label of the first sunscreen. Consider the following questions, and record your observations in a table (see table 1):
• What are the key pieces of information that are included on the front of the packaging?
• Does the sunscreen provide UVA protection, UVB protection, or both (broad spectrum)?
• What are the SPF number (e.g. 10, 15, 30) and SPF category (e.g. low, medium, high)?
• Looking at the ingredients list, what active ingredients are found in the sunscreen? w1
• What are the first 5 inactive ingredients listed on the label?
• Repeat the previous step for the different sunscreens around the classroom, and compare your findings.
• In your group, discuss the different characteristics of the sunscreens and try to classify them, taking into account the type of UV filter (UVA, UVB or broad spectrum), their active ingredients, and the SPF. You will share your preliminary conclusions with the rest of the class in a follow-up discussion.

Discuss the following questions with your students to explore the key concepts:

• Which substances are commonly used as UV filters (the active ingredients)?
• Are the active ingredients organic or inorganic substances?
• What are the main inactive ingredients found in sunscreens?
• How many of the sunscreens claimed UVA protection, UVB protection or both?
• What is the difference between UVA and UVB? What are their known health effects?
• What does ‘SPF’ mean? How is SPF calculated?
• What is the difference between a sunscreen with SPF 30 and a sunscreen with SPF 50?

Explanation

Sunscreens protect us from the Sun’s harmful rays by blocking or absorbing UV radiation. There are two types of UV radiation that can damage our skin: UVA and UVB. They affect our skin in different ways (UVA, for example, is the dominant ‘tanning’ ray, while UVB causes sunburn), and both types increase the risk of skin cancer. UVA rays are also responsible for premature ageing effects such as wrinkling.

At sea level, UVA comprises approximately 95% of the UV energy reaching Earth’s surface, and UVB comprises the remaining 5%. UVB rays have a wavelength of 280–320 nanometres (nm), while UVA rays are split into two categories: UVA1 (320–340 nm) and UVA2 (340–400 nm). SPF (sun protection factor) indicates a sunscreen’s ability to protect skin from UVB damage w2 . It is a measure of how much radiation is required to cause sunburn on protected skin (i.e. with sunscreen) relative to the amount of radiation required to produce sunburn on unprotected skin. The higher the SPF, the more UVB protection the sunscreen provides. In addition to the SPF, sunscreens are now categorised as providing low to very high protection, to ensure the labels are easy to understand.

Since the SPF only measures protection against UVB rays, it is important to choose a sunscreen that also has high UVA protection. According to EU recommendations, the UVA protection for a sunscreen should be equivalent to at least one-third of the labelled SPF. Products that achieve this requirement are labelled with the letters ‘UVA’ printed in a circle. Sunscreens that protect from both UVA and UVB do so by either combining UVA and UVB filters or by using a broad-spectrum filter.

In addition to being classified according to their SPF and UVA protection, sunscreens can be grouped depending on whether their active ingredients are organic or inorganic. Organic UV filters are a group of carbon-containing compounds that absorb UV radiation and convert it to heat energy. Inorganic filters, on the other hand, are a group of mineral oxides such as zinc oxide and titanium dioxide, which reflect UV radiation.

The active ingredients are combined with a ‘base cream’, which is made up of various inactive ingredients. This forms a product that can be easily applied to skin.

Activity 2: Formulating sunscreen

In this activity, students formulate their own inorganic sunscreen at two SPF values using zinc oxide. The aim is to learn more about the composition of sunscreens, while also exploring key concepts such as concentration, solubility, polarity and emulsions. This activity will take approximately 50 minutes.

To prepare one sample of sunscreen, each group requires:

• Lanette wax (contains a mixture of cetearyl alcohol and cetostearyl alcohol)
• Sweet almond oil
• Liquid paraffin
• Distilled water
• Water bath heated to 80 ºC
• Two 250 ml beakers
• Three 50 ml beakers
• Two glass rods
• Magnetic stirrer
• Electronic balance
• Begin by preparing an emulsion that will serve as the base cream of your sunscreen. Add the oily phase ingredients to a 250 ml beaker: 15 g lanette wax, 7 g sweet almond oil and 7 g liquid paraffin. Weigh out the ingredients using an electronic balance.
• Place the beaker inside the water bath. Mix the ingredients using a glass rod or magnetic stirrer for 5 minutes until the mixture is well combined. Leave the beaker inside the water bath.
• In a separate 250 ml beaker, add the aqueous phase ingredients: 5 g glycerine and 66 ml distilled water. Mix using a new glass rod or the magnetic stirrer.
• Keeping the oily-phase beaker in the water bath, pour the aqueous-phase solution into the oily phase, stirring continuously for 5–10 minutes until you have a homogeneous mixture: this is the base cream. Leave the beaker inside the water bath.
• In a 50 ml beaker, mix the zinc oxide with liquid paraffin in a ratio of 5:4, i.e. 2 g of zinc oxide to 2 ml (1.6 g) of paraffin.
• In a separate 50 ml beaker, measure out 4.1 g of the base cream. Add 0.9 g of zinc oxide/paraffin paste and mix them with a glass rod until combined. This creates a sunscreen that is 10% zinc oxide, which equates to an SPF of approximately 10.
• In another 50 ml beaker, measure out 3.2 g of base cream and add 1.8 g of zinc oxide/paraffin paste. Mix them with a glass rod until combined. This creates a sunscreen that is 20% zinc oxide, which equates to an SPF of approximately 20. You will use these sunscreens in the next activity.

• Which base cream ingredients are soluble only in water? Which are soluble only in oil? Justify your answers in relation to the polarity of the substance.
• Why is lanette wax essential for your formulation?
• What are the characteristics of emulsions and emulsifiers?
• What is the difference between an oil-in-water and a water-in-oil emulsion?
• Find two emulsifiers in the ingredient lists of some sunscreens from activity 1.

The base cream produced in the activity is an emulsion, since it has an oily phase and an aqueous phase. The emulsifier (which stabilises the emulsion) is lanette wax. Emulsifiers typically have a polar (or hydrophilic) head and a non-polar (or hydrophobic) tail, and they tend to have greater or less solubility in either water or oil. The lanette wax emulsifier is more soluble in oil, although also water-soluble. Emulsifiers that are more soluble in oil tend to form water-in-oil emulsions, whereas emulsifiers that are more soluble in water tend to form oil-in-water emulsions.

Activity 3: Investigating the effectiveness of UV protection

The aim of this activity is to investigate the effectiveness of the two sunscreens produced in activity 2. Using colour-changing craft beads that change colour in response to UV light (at 300–360 nm) to represent our skin, students can determine how well the two sunscreens shield the beads from UV radiation, and thus how well they protect. We found it was best to use purple or blue beads as they show changes in colour intensity best. Use the same colour beads for all experiments, i.e. all blue or all purple. Note that all UV beads start off white before they are exposed to light. The procedure takes approximately 50 minutes.

Once students have tested their own sunscreens, they should expand their investigations (see extension section) to compare a variety of other store-bought sunscreens.

Each group requires:

• Sunscreens from activity 2
• 10–12 UV beads (kept in a light-impenetrable container)
• Small transparent plastic sheets (large enough to cover four UV beads)
• Petri dish or similar (to hold the UV beads)
• Colour chart w3 or smartphone with a colour detection app (such as ‘Color Grab’ or ‘Drop – Colour Palette’)
• UV light source, e.g. torch or black light
• Laboratory stand and clamps

Safety note

Do not look directly towards UV lamps. Turn on the UV lamps only when required, and after safety instructions have been given by teachers.

• Place four UV beads in the centre of a petri dish. Position the UV lamp approximately 20 cm away from the dish, or clamp a UV torch to a stand positioned at the same distance. Ensure that the UV light source stays at the same distance throughout the experiment and that the light always illuminates downwards.
• Collect a pea-sized amount of your first sunscreen from activity 2 (10% zinc oxide) using a spatula, and spread a thin layer of the sunscreen onto the centre of the plastic sheet to cover the UV beads (approximately 4 cm in diameter).
• Place the plastic sheet on top of the beads, ensuring that the sunscreen covers the beads.
• Turn on the UV light source for 5 seconds, keeping count with a stopwatch.
• As soon as the time is up, turn off the lamp and use the colour chart or a colour detection app to record the colour of each bead. Alternatively, take a photo of the beads to compare their colours with those obtained in subsequent experiments. Ensure that you save your data and/or photos.
• Move the UV beads into a dark container so that they are not exposed to light. Add four new, unexposed beads to the petri dish.
• Repeat the procedure twice more for your first sunscreen so that you conduct the experiment three times in total.
• Follow the same procedure for your second sunscreen (20% zinc oxide), and also for two controls: one using a clean plastic sheet without sunscreen, and another using no plastic sheet.
• Compare the colour intensities of the UV beads for each sunscreen and the controls.

Discuss the following questions with your students:

• What conclusions can you draw from your experiments?
• Are your experimental results consistent with the idea of SPF?
• What were the dependent, independent and fixed variables in your experiments?
• Why should UV beads be used only as a guide to compare the effectiveness of sunscreens? What are the main disadvantages of this experimental method?

The experiment should show a clear difference in the colour of the beads in the presence and absence of the homemade sunscreens, and students should be able to observe a small difference between the use of sunscreens of 10% zinc oxide and 20% zinc oxide. The darker the colour of the beads, the more UV radiation they have absorbed, and the less effective the sunscreen. This shows students that there is a difference in the amount of UV radiation that can be absorbed by the beads, depending on the SPF of the sunscreen. This was more evident when we tested store-bought sunscreens of the same brand and type (but different SPF) in our extension experiments.

We found there was no significant difference in outcomes between the two control experiments, which tested the UV beads with and without the plastic sheet. However, using a UV sensor (see extension section), students may detect a slight difference in the amount of UV radiation reaching the beads with and without the plastic sheet.

Extension activity

Students can devise their own investigations and create new hypotheses by expanding on the previous procedure to test other sunscreens. For example:

• Compare two store-bought sunscreens (choose among sunscreens of activity 1), one of SPF 15 and the other of SPF 30, keeping the brand and sunscreen type the same.
• Compare two sunscreens of the same SPF but from two different brands.
• Compare two sunscreens of the same SPF, brand and type, but with a difference in ‘shelf life’, e.g. using one sunscreen that has only just been opened, and one that has expired.

You can make further modifications to the experiments, for example:

• Test the UV beads in sunlight, rather than under a UV lamp or torch.
• Using the same procedure, test various pairs of sunglasses to investigate their effects against UV light.
• For a more sophisticated method, use a UV sensor to investigate the effectiveness of sunscreens by measuring the intensity of UV light. Place the plastic sunscreen sheet over the sensor, rather than the UV beads, and record the sensor’s readings.

Web References

• w1 – For a list of active ingredients used in sunscreens, visit the US Food and Drug Administration (FDA) website to download a poster that outlines their proposed changes to sunscreen regulations.
• w2 – Learn more about SPF and the factors related to sun exposure on the FDA website .
• w3 – For activity 3, students can use a colour chart such as this one created by the Royal Society of Chemistry. Note that students should ignore the ‘UV Sun index’ scale.
• Visit the British Association of Dermatologists website for a factsheet on sunscreen, including details of how to apply sunscreen and tips for staying safe in the sun.

Professor Fina Guitart is a secondary school teacher of chemistry and physics. She holds a PhD in chemistry and currently works as a teacher trainer the Department of Education for the Government of Catalonia. She also teaches courses in secondary education (physics and chemistry) at the Faculty of Education at the University of Barcelona, Spain.

Professor Silvia Lope holds a PhD in biology education and currently teaches at the Pompeu Fabra University in Barcelona, Spain, on the master’s programme in secondary school science teaching.

This article is a great example of a cross-curricular project that offers learning in an active way. The activities provide the perfect mix of discussion, analysis and experiment on the topic of sunscreens and their UV protection – something that is highly relevant to teenagers.

The experiments and discussions can be used to explore a variety of topics that are central to most science curricula, and they also provide the opportunity to learn about the scientific method. The time needed for all three activities is approximately 3 hours, which – from my point of view as a teacher of chemistry, physics and biology – is time well spent.

Dr Ingela Bursjöö, science teacher, Montessori school Elyseum, Gothenburg, Sweden

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The efficacy and safety of sunscreen use for the prevention of skin cancer

• Several well-conducted randomized controlled trials with long follow-up showed that sunscreen use reduces the risk of squamous cell and melanoma skin cancers.
• Commercial sunscreens protect against the skin-damaging effects of ultraviolet radiation through either chemical or physical ingredients.
• The Canadian Dermatology Association recommends the use of an adequate dose of a broad-spectrum sunscreen with a sun protection factor of at least 30 for most children and adults, as part of a comprehensive photoprotection strategy.
• Emerging evidence suggests that some chemical sunscreen ingredients are systemically absorbed, but the clinical importance of this remains unclear; further research is required to establish whether this results in harm.
• Ultraviolet filters found within chemical sunscreens may be harmful to the environment.

In Canada, more than 80 000 cases of skin cancer are diagnosed every year. 1 Because exposure to ultraviolet radiation is estimated to be associated with 80%–90% of skin cancers, the use of sunscreen — which blocks ultraviolet radiation — is promoted as an important means of preventing skin cancers, 2 , 3 as well as sunburn and skin photoaging (see definitions in Appendix 1, available at www.cmaj.ca/lookup/doi/10.1503/cmaj.201085/tab-related-content ). Use of sunscreen has been shown to reduce the incidence of both melanoma and nonmelanoma skin cancers. 4 , 5 Both the Canadian Dermatology Association and the American Academy of Dermatology recommend the use of sunscreen for the prevention of skin cancer. 6 , 7 Yet, since the development of the first commercial sunscreen in 1928, questions regarding the safety and efficacy of sunscreen have been raised, and more recently, the impact of sunscreens on the environment has become a cause for concern. We summarize evidence related to the effectiveness and harms of sunscreen to help physicians counsel their patients ( Box 1 ).

Evidence used in this review

We conducted a targeted search of MEDLINE using a combination of the search terms “sunscreen,” “skin cancer,” “melanoma,” “squamous cell carcinoma,” “basal cell carcinoma,” “photoaging,” “safety” and “environment” to identify studies published from 1984 to 2020. We particularly sought randomized controlled trials, systematic reviews and meta-analyses relevant to this article’s clinical questions. We also identified relevant review articles, basic science publications and institutional guidelines. We supplemented our search with literature from our own collections.

How do sunscreens work?

Sunscreens contain chemical (organic) or physical (inorganic) compounds that act to block ultraviolet radiation, which is light with wavelengths shorter than visible light (subdivided into ultraviolet A [UVA]1, UVA2, ultraviolet B [UVB] and ultraviolet C [UVC]), as shown in Figure 1 . Generally, the shorter the wavelength, the greater the potential for light radiation to cause biological damage. Sunscreen filters are active against UVA1, UVA2 and UVB radiation. Chemical filters, such as oxybenzone, avobenzone, octocrylene and ecamsule, are aromatic compounds that absorb high-intensity ultraviolet radiation, resulting in excitation to higher energy states. When these molecules return to their ground states, the result is conversion of the absorbed energy into lower-energy wavelengths, such as infrared radiation (i.e., heat). 8

Schematic representation of the electromagnetic spectrum of light, emphasizing ultraviolet radiation (UVR) frequencies and their effect on human skin. Generally, the shorter the wavelength of radiation, the greater the potential for biological damage. Note: UVA = ultraviolet A, UVB = ultraviolet B, UVC = ultraviolet C. Sunscreen filters are active against UVA1, UVA2 and UVB radiation.

Physical sunscreen filters, such as titanium dioxide and zinc oxide, reflect or refract ultraviolet radiation away from the skin; however, experimental studies have shown that when particle sizes are very small, as in micronized sunscreens, the mechanism of action is similar to that of chemical filters. More specifically, micronized zinc oxide and titanium dioxide behave as semiconductor metals, which absorb ultraviolet light throughout most of the electromagnetic spectrum. 9 The sunscreen ingredients that are currently approved by Health Canada are listed in Table 1 . 10

Sunscreen ingredients approved by Health Canada 10

Note: PABA = para-aminobenzoic acid, UVA = ultraviolet A, UVB = ultraviolet B.

What is the effectiveness of sunscreens in preventing photoaging and skin cancer?

Evidence from observational studies, 11 a large randomized controlled trial (RCT) 12 and smaller, nonrandomized experimental studies 13 – 15 support the effectiveness of sunscreens in preventing the signs of photoaging, including wrinkles, telangiectasia and pigmentary alterations induced by ultraviolet radiation. 11 – 15 Despite the challenges of studying skin cancer, owing to its multifactorial pathogenesis and long lead time, the following evidence supports the use of sunscreen in the prevention of skin cancer.

Experimental studies from the 1980s and 1990s showed that sunscreens protect against cell damage consistent with carcinogenesis in animal models. 16 , 17 A well-conducted community-based 4.5-year RCT of 1621 adult Australians, with follow-up for more than a decade, found a 40% lower incidence of squamous cell carcinomas among participants randomized to recommended daily sunscreen compared with participants assigned to use sunscreen on a discretionary basis (rate ratio 0.61, 95% confidence interval [CI] 0.46 to 0.81). 4 , 18 However, the incidence of basal cell carcinomas was not significantly reduced, possibly owing to the protracted pathogenesis of basal cell carcinomas. 18 Almost 15 years after the completion of the study, participants who used sunscreen daily throughout the 4.5-year study period showed a significantly reduced risk of invasive melanoma (hazard ratio [HR] 0.27, 95% CI 0.08 to −0.97), although very few invasive melanomas were noted, given the long lead time for this type of tumour. 5 A predefined subgroup analysis in this trial confirmed that regular use of sunscreen over a 4.5-year period can arrest signs of skin aging caused by photodamage. 12 Another large Australian RCT showed a significantly reduced rate of development of actinic keratoses (a precursor to squamous cell carcinoma) among participants randomized to regular use of sunscreen, compared with controls who used a nonactive base cream over 1 summer season (rate ratio 0.62, 95% CI 0.54 to −0.71). 19

In organ transplant recipients, a population at high risk of morbidity and death from skin cancer, a prospective single-centre study of 120 matched patients showed that the use of sun protection factor (SPF) 50 sunscreen over 24 months reduced the development of actinic keratoses, squamous cell carcinomas and, to a lesser extent, basal cell carcinomas. 20 Recent meta-analyses have not supported the findings of these RCTs, finding no significant effectiveness of sunscreen for preventing either melanoma or nonmelanoma skin cancers. 21 , 22 However, these meta-analyses included studies with retrospective designs with methodological inconsistencies among studies, and 1 included studies that used only UVB filters (rather than broad-spectrum sunscreens). 21 Overall, the highest-quality evidence available suggests that sunscreens do prevent skin cancer.

Who should use sunscreen?

The American Academy of Dermatology recommends regular sunscreen use with an SPF of 30 or higher for people of all skin types, 23 although skin cancers are far more prevalent in White individuals than people with darker skin. 24 There have been no studies to assess the effectiveness of regular sunscreen use in reducing the risk of skin cancers among people who are not White.

For children older than 6 months, as well as adults, the Canadian Dermatology Association recommends the use of broad-spectrum sunscreens with an SPF of 30 or greater. 7 Split-face studies have shown that sunscreens with an SPF of 100 are superior to sunscreens with an SPF of 50 for preventing sunburns under actual use conditions, in both a beach setting 25 and a high-altitude skiing setting. 26

Health Canada does not recommend the use of sunscreen for children younger than 6 months because of the theoretical risk of increased absorption of sunscreen ingredients as a result of higher body surface-to-volume ratios and thinner epidermis. 27 The mainstays of sun safety in infants include sun avoidance and protective clothing. 28 If sunscreen is used in infants, experts suggest washing it off as soon as it is no longer needed, 29 and favouring physical sunscreens over chemical varieties.

How should sunscreen be applied?

Observational studies have shown that consumers typically underapply sunscreen, with standard use ranging between 20% and 50% of the recommended application. 30 – 32 However, using sunscreens with higher SPFs may compensate for underapplication. 26 For example, when a sunscreen with an SPF of 50 is applied under real-world conditions, the sunscreen may provide an SPF of only 25.

A 2015 Canadian consensus meeting agreed that the wording “apply sunscreen generously” was most appropriate, given differences in body habitus of the public. 33 Figure 2 offers a rough estimate of the quantities of sunscreen that should be applied by a person of average height and build, based on advice from the Canadian Cancer Society and the American Academy of Dermatology.

Visual aid to guide the correct application of sunscreen for a person of average height and body habitus, based on advice from the Canadian Cancer Society and the American Academy of Dermatology.

Although product labelling often suggests that sunscreens should be applied 15 to 30 minutes before going outdoors, 34 in a recent study, immediate protection against ultraviolet radiation occurred after sunscreen application, although protection after water exposure was not examined. 35 Therefore, it may be prudent to wait 15 to 30 minutes if water resistance is required.

Recent experimental studies have shown that sunscreen remains on the skin at the desired SPF for as long as 8 hours after a single application, 35 – 38 suggesting that historical advice to reapply sunscreen every 2–3 hours need not be followed even when individuals are physically active. However, reapplication is suggested when the likelihood of sunscreen having been removed is high, such as after sweating, water immersion, friction from clothing and exfoliation from sand. 39 – 41 When swimming or sweating are anticipated, water-resistant sunscreens should be used. 40

Spray-on sunscreens are less desirable than cream-based ones, for several reasons. Wind can disperse the sunscreen, resulting in inadequate application. Moreover, because spray-on sunscreens are often fast drying, and sometimes not clearly visible once sprayed onto the skin, it is difficult to determine whether application was homogeneous. 42 Aerosolized sunscreens are also flammable, and several incidences of combustion on the skin have been reported after exposure to open flames, even after the sunscreen has been allowed to dry. Finally, the potential risks associated with inhalation of aerosolized sunscreens have not been adequately studied. 43

What are the key safety concerns?

Skin reactions.

The most common reported adverse reactions to sunscreens include subjective irritation (e.g., stinging and burning) without a rash, irritant contact dermatitis and comedogenicity. Rarely, chemical sunscreen ingredients may also cause allergic contact dermatitis and photoallergic contact dermatitis, with the most commonly implicated allergenic ingredients being octocrylene, oxybenzone and octyl methoxycinnamate. 44

Absorption of sunscreen

In 2019, a small RCT with 24 participants, sponsored by the United States Food and Drug Administration, showed systemic absorption of 4 sunscreen ingredients: oxybenzone, avobenzone, octocrylene and ecamsule. 45 When applied under maximal use conditions, over 4 consecutive days, blood levels for these compounds exceeded those recommended by US Food and Drug Administration guidelines. 45 Moreover, the investigators noted long half-lives for each of these ingredients, suggesting that regular sunscreen use may lead to accumulation within the body. 46 A follow-up study confirmed these findings. 47 However, most people use far less than this volume of sunscreen and, despite their findings, the study investigators encouraged the use of sunscreen given its known protective effects, as the clinical importance of absorption of these ingredients is not yet known. Further research is needed to determine whether there are any potential health sequelae from absorption of sunscreen ingredients.

In contrast to chemical sunscreen ingredients, physical sunscreens are not systemically absorbed. An in-vitro study found that less than 0.03% of zinc nanoparticles penetrated the uppermost layer of the stratum corneum, and no particles were detected in the lower stratum corneum. 48 Physical sunscreens historically were less cosmetically appealing than chemical sunscreens, leaving a white residue on the skin, potentially leading to underapplication. Advances in formulation and micronization of physical ultraviolet radiation filters has led to more cosmetically acceptable physical sunscreens. 49

Endocrine effects

Low-quality evidence has led to concerns about possible estrogenic and antiandrogenic effects of chemical sunscreens. Although a recent meta-analysis found that oxybenzone is associated with reproductive adverse effects in fish, the summarized literature was nonuniform and the results therefore uninformative. 50 Among human research participants, a prospective study noted reduced fecundity when men were exposed to benzophenone-2 and 4-hydroxybenzophenone, but the findings could be explained by study confounding. 51 One systemic review, which evaluated both animal and human studies, found that high levels of oxybenzone exposure during pregnancy were associated with decreased gestational age in male neonates and decreased birthweight in female neonates. 50 However, high heterogeneity limited the usefulness of the study findings. 50

How do sunscreens affect the environment?

Some recent studies have reported that chemical sunscreen ingredients are detectable in various water sources 52 , 53 and may persist despite waste-water treatment processing. 54 An additional recent concern is the detection of sunscreen filters in the tissues of various fish species, raising the possibility of bioaccumulation and biomagnification. 55

The effects of sunscreen ingredients on coral reefs are a current focus of scientific investigation. In-vitro studies have shown that oxybenzone affects coral reef larvae 56 and may be implicated in coral reef bleaching. However, possible confounding variables include increased ocean salinity and temperature associated with global warming. 55 These preliminary studies have prompted the banning of oxybenzone and octinoxate in some jurisdictions. 57

What additional photoprotective measures may be used?

Sunscreen is only one part of a comprehensive photoprotection strategy. It is important to counsel patients regarding behaviours for avoiding ultraviolet radiation, including the use of wide-brimmed hats, eye protection (e.g., “wrap-around” sunglasses with ultraviolet radiation protection) and seeking shade when the ultraviolet index is above 3 (usually 11 am–3 pm, April to September in Canada). 33 Typically, thicker clothing with tighter weave fabrics — such as polyester and cotton, or nylon and elastane (i.e., Spandex, Lycra) — and darker colours offer greater protection. 58 , 59 Clothing has been designed for sun protection with an ultraviolet protection factor (UPF) up to 50. 28 All clothing will become less photoprotective if it is wet or stretched. 59

Potential new sunscreen technologies

Topical photolyases and antioxidants (vitamin C, vitamin E, selenium and polyphenols found within green tea extracts) are emerging as potential agents of topical and nontopical photoprotection. Antioxidants cannot yet be stabilized within sunscreen formulations to remain biologically active. Studies have established that sunscreens that claim antioxidant activity have little to no actual antioxidant activity. 60 – 62

Photoprotective agents taken orally, such as niacinamide and Polypodium leucotomos extract, which is derived from a fern native to Central and South America, are used as agents for prevention of photodamage. There is evidence from small RCTs that P. leucotomos extract increases the minimal erythema dose of sun exposure without significant adverse effects, and is helpful for dermatologic diseases induced by ultraviolet radiation, such as polymorphous light eruption and solar urticaria. 63 – 65

Nicotinamide, also known as niacinamide, is the active amide form of niacin (vitamin B3). However, unlike niacin, it does not cause cutaneous flushing. Nicotinamide has been shown in early studies to enhance DNA repair and decrease the formation of cyclobutene pyrimidine dimers in human keratocytes. 62 In one phase III RCT, which has not been replicated, nicotinamide 500 mg twice daily was associated with a decreased rate of development of both actinic keratoses and nonmelanoma skin cancers over a 12-month period. 66 However, the skin cancers that did occur tended to be high-grade malignancies.

Exposure to ultraviolet radiation is directly harmful and has been associated with the development of skin cancers, which are common in Canada. High-quality evidence has shown that sunscreen reduces the risk of developing both melanoma and nonmelanoma skin cancer. Therefore, physicians should counsel patients on photoprotection strategies, including avoiding midday sun, seeking shade and wearing protective clothing, as well as using sunscreen if sun exposure cannot be avoided. Presently, the Canadian Dermatology Association recommends the use of a broad-spectrum sunscreen with an SPF of at least 30 for people older than 6 months, for photoprotection. Low-quality evidence has shown that some chemical sunscreen ingredients are systemically absorbed and may be contributing to environmental damage; people who are concerned may consider using physical sunscreens as an alternative. Research on the safety and efficacy of established sunscreens and novel agents is ongoing.

Competing interests: Toni Burbidge reports receiving honoraria from AbbVie, Celgene, Janssen, Leo Pharmaceuticals and Lilly. No other competing interests were declared.

This article has been peer reviewed.

Contributors: All of the authors contributed to the conception and design of the work, and the acquisition, analysis and interpretation of data. All of the authors drafted the manuscript, revised it critically for important intellectual content, gave final approval of the version to be published and agreed to be accountable for all aspects of the work.

Lesson Preview: Sunscreen Science

Because Learning! Lesson Samples , STEM 0

In our Lessons portal, Because Learning has over 130 (and counting) Lessons for your classroom. Check out a preview of our Lesson format with one of our most popular choices, Sunscreen Science!

Note:  the buttons and fields don’t work on this sample. But when you access Lessons via our online platform, the interactive elements you see allow students to engage with the Lesson content.

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• Our Experiment Guide at the bottom of the lesson is perfect for teachers (included with every lesson!)
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Sunscreen Science

Do more expensive brands of sunscreen protect from uv radiation better, worse or the same as less expensive sunscreen, step 1: gather supplies.

What you’ll need for this experiment:

• Plastic wrap
• Permanent Marker
• Sunscreen with one variable.  Suggested variables are:
• Same SPF, different brands
• Same SPF, same brand, different type (lotion, spray, stick, etc)
• Same SPF, same brand, different expiration dates.

Step 2: Background Information

What is UV light?

We all know that the sun produces light–scientists call it  electromagnetic radiation .  The  electromagnetic radiation  that is produced by the sun is made up of a bunch of different  wavelengths .  Only a small portion of the  wavelengths  can be seen by humans.  We call this small portion  visible light .  The picture below shows the  electromagnetic spectrum: 

This diagram of the  electromagnetic spectrum  arranges the  electromagnetic radiation  by  wavelength .  At the far left end of the diagram is the  electromagnetic radiation  that has a long  wavelength  called  infrared light  (or  IR  for short).  At the far left end of the diagram is the  electromagnetic radiation  that has a short  wavelength  called  ultra-violet light  ( UV  for short).

Some living creatures are able to see  UV light  with their eyes.  Bees use  UV light to help them navigate to the best flowers from which to collect pollen.  The short video clip below illustrates how bees use  UV light:

When human skin is exposed to sunlight, it either burns or tans–that is because  UV light  has a short enough  wavelength  to break the chemical bonds in skin tissue.  Too much exposure to sunlight and  UV light  can cause serious, irreversible skin damage–which is why sunscreen is so important!

Sunscreen works by scattering and absorbing  UV light.   When you put sunscreen on, it is like putting on an invisible barrier that prevents  UV light  from penetrating your skin.

Step 3: Experiment Setup

For this experiment, you need to decide what you are testing and what your question is going to be. Three suggestions were given above in the materials list.

You can pick one of these or you can devise your own experiment.  Remember, each sunscreen has at very minimum 3 variables:

• Sunscreen Brand
• Expiration Date

Pick one variable to change and test and keep the others the same–these will be your constants.  For example, I would like to test expiration dates.

• My question is:  Does expiration date affect how well sunscreen blocks UV light?
• My variable is going to be the expiration date.
• My constants are going to be SPF number and brand.

In other words, the sunscreens I am testing are the same brand and SPF, but they have different expiration dates.

Now it is time to make your prediction or hypothesis.

Step 4: Experiment Procedure

1.  To setup your experiment, you need to get a piece of plastic wrap and mark as many squares on the plastic wrap as you have sunscreen to test, you should also have one square that doesn’t have any sunscreen–this is your control.

2.  Label each square with the name and SPF of the sunscreen you are testing and then dab a bit of each sunscreen in the proper square.  Spread out until the entire square is covered.

Note:  Your squares should be slightly bigger than the Sensor Board.

3.  Wire up your Sensor Board using the diagram below:

4.  The code block below tells the microcontroller to access the Ultra Violet (UV) sensor.  Plug in your microcontroller to your computer with the USB cord and press the “Run on Arduino” button.

5.  To access the UV data, click on the “Connect to Arduino” button below.

6.  Take your sunscreen plastic wrap, your Sensor Board, and your computer outside.  Test each square on the plastic wrap by placing the sensor board underneath the sunscreen smeared plastic.

7. Record your data in your lab notebook.

Step 5: Conclusion

Use your lab notebook and the data you collected to draw a conclusion.  What does the data tell you?

Now that you’ve tested one variable related to sunscreen and UV readings, try repeating the experiment and see if you get the same results.  Science is all about making sure the results from an experiment are repeatable over many tries.

Or, how about a new experiment altogether?  Pick a different variable to change from the suggested list above?  How would you set up that experiment–what would you need to control and what would you need to vary?  Head on over to our  UV Sensor  guide to gather UV readings and data.

Did you like the Sunscreen experiment?  Try following our experiment guide for testing cost vs effectiveness of sunglasses– Sunglasses .

Now try this!

Take it to the next level and learn more about the sun’s energy in this experiment! 

Solar ovens

  To access more information about this experiment such as NGSS alignment, pacing, essential questions, and inquiry-based teaching practices, check out the  Experiment Guide .

Photo Credits:

UV and Visible Light Portrait by  Spigget (Own work), via Wikimedia Commons Electromagnetic Spectrum:  Science Kids at Home Sunscreen gif:  Giphy

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Simple Summer Science Sunscreen Experiment

• Kindergarten

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Protecting your skin from the sun’s UV rays may be a hard, abstract concept for kids to understand… at least until they get a sunburn. This simple  sunscreen experiment allows kids to learn about the importance of using sunscreen this summer. This  summer science  is perfect for all ages from kindergartner, first grade, 2nd grade, 3rd grade, 4th grade, 5th grade, and 6th graders. All you need are a few simple materials to try this  sunscreen construction paper experiment.

Sunscreen Experiment

Summer is the perfect time to get outside and enjoy the warm, bright sun. But how careful are we about protecting our skin from the sun’s UV rays? Too much exposure to the UV Radiation can lead to skin cancer, wrinkles and age spots. When the sun hits your skin it tells your body to protect itself by producing melanin , a brown pigment that darkens the cells of our epidermis (the technical term for skin). Sunscreen, sunglasses, hats, and layers of light clothing are important to protect us from the effects of too much time in the sun. In this fun  sunscreen experiment we are going to look at the effects the sun can have and if sunscreen can help slow or stop those affects. THis simple  summer science experiment is fun for all ages from preschoolers, kindergartners, grade 1, grade 2, grade 3, grade 4, grade 5, and grde 6 student too.

Sunscreen Experiment on Paper

All you need are a few simple materials to try this  sunscreen paper project .

• colored construction paper (we used orange)
• dark colored construction paper
• plastic wrap

Sunscreen on paper experiment

Start by cutting 4 squares or people shapes out of your colored construction paper. Any color of dark colored construction paper should work great.  Write on the back of each person: control, sunscreen, hat, or sunglasses. Cut out hat and sunglasses of black construction paper and place on the appropraite person.

Sunscreen science experiment

Now wrap each piece in plastic wrap. Put sunscreen over the figure marked sunscreen  only .

The great sunscreen experiment

Put your construction paper person out in the sun following the conditions on the reverse side for 1 week. Make predictions or hypothesis of what you will see.

• no protection on the first, just wrapped in plastic wrap
• apply sunscreen – use the type you would typically use
• set a hat over top of the hat paper
• set sunglasses over the final paper

Sunscreen construction paper experiment

Check on your papers. Did any of them fade?  Which one worked best? Adding an extra layer like a hat or sunglasses protects delicate areas such as your eyes and face from sunburns that may result in skin cancer and sun damage.

Sunscreen science fair project

The thicker the layer of sunscreen or the highter the SPF the better protection it should have provided to your paper skin.

Sunscreen experiments

Sunscreen comes in different strengths called the SPF (Sun Protection Factor) to tell us how much it protects our skin; the highter the more protection. Try your experiment again and this time use a different SPF factor for each of your construction paper test subjects.

Looking for more  outdoor activities for kids and  things to do in the summer ? Your toddler, preschool, pre k, kindergarten, and elementary age kids will love these fun ideas to keep them busy all summer long:

• Marshmallow Shooters – go over 30 feet!
• 2 ingredient Easy Slime Recipe
• How to Make a Lava Lamp – it’s super EASY!
• Kids will no nuts over this simple Pop Rock Experiment
• Handprint Strawberry Craft for Summer
• Grow Your Own Crystals
• Water Balloon Experiment – exploring densit with an EPIC summer activity for kids
• Simple Lemon Volcano Summer Experiment for Kids
• Amazing Bubble Painting
• Mind Blowing Color Changing Playdough
• 25 EPIC Water Balloon Games

Summer Activities for Kids

• Vibrant Sidewalk Washable Spray Paint for Kids
• Egg Shell DIY Chia Pet Craft – Silly Spring / Summer Activities for Kids
• Grass Head Craft for Kids
• Blow GIANT bubbles with this Homemade Bubble Solution
• Pool Noodle Airplane Craft
• Outrageously FUN Bubble Painting
• Pasta Animal Crafts for Kids
• Bleeding Tissue Paper Fireworks Craft
• Beautiful Flower Suncatcher Craft
• 30 Fun June Crafts for Kids
• Must try Lego Zipline
• EASY Stained Glass Pasta Art Project for Kids
• Exploding Watermelon Science Experiment
• Bubble Wrap Puffy Paint Ice Cream Craft
• Fun-to-play-with Ocean Slime
• Homemade Chalk Recipe
• 75+ FUN Scavenger Hunts for Kids

Fun Summer Activities for Kids

• Ice Cream Edible Playdough
• Whip up a batch of Kool Aid Playdough – it smells amazing!
• I Spy DIY Bottles are quick, easy and FUN!
• Amazing Tin Foil Art Project for Kids of all Ages
• Vinegar and Baking Soda Rocket Science Experiment for Kids
• Summer Bucket List Printable with Ice Cream Theme
• How to Make Ice Cream in a Bag
• Ice Cream Playdough Patterns
• Head to the zoo with this FREE Zoo Scavenger Hunt – lots of choices for all ages!
• Make your favorite animal with one of these 100 animal crafts
• Try one of these fun Animal I Spy Printables
• Epic Squirt Gun Painting
• Play with your food using this goldfish counting activity
• After seeing the frogs at the pond, grab this free life cycle of a frog worksheet
• Avoid the summer learning loss by practicing math with these crack the code worksheets
• First Day of Summer Craft
• Create this gorgeous stained glass art for kids
• 107 Epic Summer Activities for Kids
• Outrageously FUN Balloon Drop Painting

Beth Gorden

Beth Gorden is the creative multi-tasking creator of 123 Homeschool 4 Me. As a busy homeschooling mother of six, she strives to create hands-on learning activities and worksheets that kids will love to make learning FUN! She has created over 1 million pages of printables to help teach kids ABCs, science, English grammar, history, math, and so much more! Beth is also the creator of 2 additional sites with even more educational activities and FREE printables – www.kindergartenworksheetsandgames.com and www.preschoolplayandlearn.com. Beth studied at the University of Northwestern where she got a double major to make her effective at teaching children while making education FUN!

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Thank you for this amazing idea! Such an easy way to understand the entire “drama” about applying sunscreen. I love it! 💕

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Science project, a beautiful sunny day.

Grade Level: 6; Type:  Environmental

The purpose of this project is to test sunscreens from the lowest number to the highest. People depend on sunscreen to protect their skin from the sun’s ultraviolet radiation. People believe that a higher number equates to greater protection.

Research Questions:

• Does sunscreen block the sun’s ultraviolet radiation? 
• Does a higher SPF number protect skin more than a lower number?

Ozone in the earth’s atmosphere filters out much of the sun’s harmful ultraviolet radiation. Chemicals produced by humans have been harming that protective layer. In the 1970s, scientists noted a thinning of the ozone over Antarctica that grows each spring, increasing the danger of ultraviolet radiation as it shines on earth’s surface and humans.

In this experiment, the independent variable is the sunscreen SPF applied to the plastic. The dependent variable is the exposure of the sun-sensitive paper. The constants include the photo paper, the plastic bags and the conditions.

• Sunscreens with a range of SPF numbers. For example, 15, 30 and 45 or 15 and 70. 
• Plastic bags—as many as the number of sunscreens plus one for the control.
• Sun-sensitive paper. (This can usually be found at kids’ stores that stock lots of crafts.)

Experimental Procedure:

• Close the blinds or shades in a room to block the natural light.
• Label the plastic bags with the SPF number for the sunscreen being tested.
• Place one square of sun-sensitive paper inside each of the plastic bags.
• Place three drops of one sunscreen on the outside of the bag labeled with its number. Spread the sunscreen as evenly as possible.
• Repeat the step above with the other sunscreens.
• Leave one bag untreated as the control.
• Place the bags outside in direct sun, making sure that they receive equal light.
• Bring them back inside after 3 minutes or one of the squares—usually the control—turns completely white.
• Observe the sun-sensitive squares and make conclusions about the effectiveness of each sunscreen.

The results of the experiment might be visually represented by a modified graph:

Terms/Concepts: Global warming; Ozone; Ultraviolet radiation

• Global Warming , Seymour Simon (2010).
• http://www.pewclimate.org/global-warming-basics/kidspage.cfm .

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Do your own spf testing.

Finally, they’ll understand why you’re always encouraging them to put on their sunscreen

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Download a PDF of this experiment

Anyone who’s been the recipient of an eye-roll from a kid after you’ve told them to put on their sunscreen will appreciate this educational project. Once they see the effect that the sun has on objects, kids will be able to understand that there’s actual science behind all of your nagging.

Using sunscreen and sun-sensitive objects, your kids will learn how to filter UV light, the effectiveness of different SPF numbers, and why sunscreen is so important. Sorry, you’ll still have to nag them, though.

GATHER THIS:

• Plastic wrap
• Sunprint Paper
• Sunscreen with different SPFs

THEN DO THIS:

• Fill your shoeboxes with the UV beads and pieces of sunprint paper (make sure to set up in the shade). You can tape down the materials so they don’t move around.
• Using a different SPF for each box, smear sunscreen on the UV beads and sunprint paper. Remember to leave one box sunscreen free!
• Cover the top of the boxes with plastic wrap.
• Place your boxes so that they receive direct rays from the sun. You can use an object to prop up your box.
• Check your boxes every 30 minutes. Compare the color of the testing materials. Your testing materials as well as the testing boxes can be used again and again unless the sunblock has been wiped off.
• What happened to the sun-sensitive items?
• What was the difference between the items coated with sunscreen vs. unprotected?

WHAT IS HAPPENING?

The SPF number is supposed to be an indication of how long the sunscreen is effective. To determine this in minutes, multiply the SPF by 10. For example, SPF 30 = 300 minutes (30 x 10), or 5 hours. The height of the sun affects the amount of radiation received. If the sun is really high in the sky the UV radiation received by your skin is greater than when the sun is lower in the sky.

WHAT THIS TEACHES:

Skills: Observation

Themes: Light and energy, health

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• Open access
• Published: 28 October 2023

A novel online survey approach designed to measure consumer sunscreen application thickness—implications for estimating environmental emissions

• Andrea M. Carrao   ORCID: orcid.org/0000-0003-3971-787X 1 , 2 ,
• James C. Coleman II 2 ,
• Jeff J. Guo 1 &
• Harshita Kumari 1  

Journal of Exposure Science & Environmental Epidemiology ( 2023 ) Cite this article

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Metrics details

The effects of ultraviolet (UV) filters in the aquatic environment have been well studied, but environmental exposures remain unclear and understudied. Consumer usage directly influences the amount of sunscreen products, and subsequently UV filters, potentially released into the environment.

To conduct a literature review of previous research into sunscreen application thickness, develop a questionnaire protocol designed to semi-quantify sunscreen usage by US consumers, and conduct a large-scale survey to determine a sunscreen application thickness (to face and body) that is more refined than conservative defaults. The United States Food & Drug Administration (US FDA) recommends a sunscreen application rate of 2 mg/cm 2 . This value is typically used as a worst-case assumption in environmental exposure assessments of UV filters.

Designed a novel approach to estimate lotion sunscreen application thickness using an online questionnaire protocol employing visual references and self-reported height and weight of the respondents. A literature review was also conducted to collect historical sunscreen usage.

Over 9000 people were surveyed in the US, and after the dataset was refined, their sunscreen application thickness was estimated based on calculated body surface area and reported sunscreen amounts. The mean and median values for survey respondents are 3.00 and 1.78 mg/cm 2 , respectively, for facial application thickness and 1.52 and 1.35 mg/cm 2 , respectively, for body application thickness. Earlier research from 1985–2020 reported 36 of the 38 values are below the US FDA’s recommended application thickness of 2 mg/cm 2 (range 0.2–5 mg/cm 2 ).

Impact statement

This web-based survey is the first of its kind, designed specifically to quantify sunscreen application in a large and diverse set of consumers. This method provides a greater reach to larger populations thus enabling more granular data analysis and understanding. Exposure assessments of sunscreen ingredients typically use conservative parameters. These data can refine those assessments and allow for more informed and science-based risk management decisions.

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Introduction.

Solar ultraviolet (UV) radiation is a known human carcinogen [ 1 ]. Sunscreens and other sun protection products protect people from the harmful effects of UV radiation [ 2 ] by using organic and inorganic ingredients known as UV filters. UV filters can be used in various combinations and concentrations in skincare product formulations to provide broad-spectrum protection against premature aging and various skin cancers caused by sun exposure. Protection against UV radiation is measured by a numerical sun protection factor (SPF) [ 3 ]. While sunscreens play an important role in protecting human health, in recent years there have been numerous scientific and media publications investigating the potential impact of UV filters on environmental health [ 4 , 5 , 6 , 7 ]. The potential hazard of organic UV filters in the aquatic environment has been well studied, but environmental exposure(s) remain(s) understudied [ 8 ].

Consumer habits and practices directly influence the amount of sunscreen and sun protection products, and subsequently UV filters, potentially released into the aquatic environment (i.e.,). Therefore, it is critical to understand consumer use of and preferences for sunscreens and sun protection products when conducting environmental risk assessments (ERA). In the United States, the Food & Drug Administration (US FDA) is responsible for the regulation of all products that claim sun protection under the Over-the-Counter (OTC) Sunscreen Monograph. From this point forward, all sun protection products will be referred to as sunscreens including those that are not designed specifically for use at the beach but instead for daily/routine SPF protection. The US FDA’s standard sunscreen test methods for determining SPF mandate a dermal application of 2.0 milligrams per centimeter squared (mg/cm 2 ) [ 3 ], which the agency also recommends for consumer use (i.e., application thickness). This value is often used as a default assumption in environmental exposure and risk assessments. However, research over the years indicates that the amount of sunscreen products applied by consumers may be less than the dose used to determine SPF values [real-world application amounts reportedly range from 0.2–1.27 mg/cm 2 ] [ 9 , 10 , 11 , 12 ]. Much of this research determined the application thickness amount by measuring how much of the product was applied by volunteers and the application site’s surface area. Generally, these studies were conducted in specific sub-populations (e.g., skin cancer survivors, beach tourists, etc.). Additionally, there has been little research around routine sun protection habits and practices, including application to the face as part of a daily skincare regimen and the increase in multi-function skincare products with the additional benefit of sun protection (e.g., moisturizing plus SPF). Therefore, new methods are needed to estimate sunscreen application and additional research is needed to determine if previously published application thickness values are representative of the general population and account for more routine use.

In 2022, the National Academies of Sciences, Engineering, and Medicine (NASEM) published the consensus study report Review of Fate, Exposure, and Effects of Sunscreens in Aquatic Environments and Implications for Sunscreen Usage and Human Health [ 13 ]. This report reviews the state of the science “on the sources and inputs, fate, exposure, and effects of UV filters in aquatic environments, and the availability of data for conducting ERAs.” The report acknowledges that consumer behavior directly affects the environmental exposure of UV filters from sunscreen products. The NASEM report identified several data needs for environmental exposure including amount and type of sunscreen applied, rates of sunscreen application per person, and body coverage of sunscreen.

However, there are several challenges with conducting sunscreen application investigations. They are resource intensive, requiring human subjects and time to conduct studies with an acceptable sample size. Due to the resources required, these studies often target study populations of interest to the investigators. Therefore, alternative methods requiring fewer resources that can be applied to understanding the habits and practices of the general population are still needed. An online platform is one option to reach a larger number of people, increasing the statistical power of the investigation, and allowing more granular analysis of the results. Using this approach, the sunscreen application thickness can be estimated using a visual reference (amount applied) and the volunteers’ disclosed height and weight (skin surface area).

The objective of this research was to develop a web-based survey protocol designed to quantify sunscreen usage by general US consumers, conduct a large-scale survey to determine the application thickness of sunscreen products to participants’ face and body, and perform a literature review of previous research into sunscreen application thickness. Using an online platform to reach a large and diverse sample set, participants were asked about their sunscreen use in general and the amount applied by comparing their use to a visual reference with measured dispensed sunscreen amounts. The desired outcome was to generate a more accurate estimate of dermal application rate of sunscreen products based on current consumer use patterns and preferences that can be used to estimate environmental exposure to UV filters more accurately.

Online survey of sunscreen usage

An online survey was conducted of the general population in the United States of America. The objective of the survey was to quantify the amount of sunscreen consumers use per sunscreen application. The questionnaire (see Appendix  S1 ) queried participants about their general sunscreen habits, if any, and how much sunscreen they typically apply to the face and both arms. A previous study was conducted using an online survey in Korea to identify common chemicals contained in household and personal care products and how much the respondents use of each product with the goal of conducting an aggregate human exposure assessment [ 14 ]. For this research, the survey method was refined with the addition of visual reference photos (Fig.  1 ) to aid participants in selecting the amount of sunscreen they typically apply per application.

The visual reference includes photos of a measured mass of sunscreen in a hand plus food examples to aid respondents in choosing an estimated sunscreen application amount to their face and both their arms.

The panel included adults between 18–70 years old that reside in the United States of America. Data from the United States Census Bureau were used to determine quotas for participant genders, ethnicities, ages, and states of residence. Participant ethnicities were included to address possible cultural differences in sunscreen usage among subpopulations. Non-Caucasian ethnicities may be under-studied in sunscreen-related research. To account for this, the present study intentionally over-sampled for African American participants (up to 35%) and balanced the remaining participant ethnicities according to US Census data (see Table  S1 ).

The questionnaire consisted of multiple-choice questions regarding demographic characteristics, sunscreen usage behaviors, reasons for usage, etc. Participants were asked if they applied sunscreen in the last 12 months. If the answer was yes, the participant was directed to a set of sunscreen user questions. If the answer was no, the participant was directed to a set of sunscreen non-user questions.

Candidates were invited to participate in the online self-administered survey hosted by Qualtrics ( www.qualtrics.com ). Qualtrics uses a mixed-method to recruit individuals. Respondents that previously registered with Qualtrics received a generic email invitation to participate in this study. If the participant agreed to participate, the link in the invitation email directed them to a detailed informed consent form. The participant was asked to review the informed consent and select “agree” to continue with the questionnaire or “disagree” to stop completion of the questionnaire. Double opt-in systems help to ensure data quality by screening out marginally-interested participants. This survey relied on participant self-reporting as the research team had no interaction with them.

After reviewing the results from the initial survey, a second follow-up survey was also conducted with an improved questionnaire. Improvements included refined instructions and reduced survey length to lessen the risk of survey fatigue. The objective of this follow-up survey was to refine the face application thickness estimation due to the observed variance of the initial survey. The follow-up survey was conducted in the United States to test the hypothesis that improved instructions would provide a better-quality (i.e., less varied) dataset. In addition, the instructions for selecting the representative sunscreen amount for application to their face and both their arms had clarified language and pictures added to indicate the application area of interest (see SI Appendix  S2 ). This was done to remove possible ambiguity in the question being asked and clarify that the application site of interest was only the facial area and should not include the participant’s ears, neck, top of head, chest, etc. This survey was sent via SurveyMonkey to the general population but was screened for face sunscreen users, unlike the initial, larger survey. The platform provider was different for this study due to contract changes; however, the questions were programmed so they would be presented to the participants in the same format as the initial study. Two questions were added to qualitatively assess the participants’ facial sunscreen use.

Ethics approval was obtained from the University of Cincinnati Institutional Review Board (IRB) before each survey was initiated (UC IRB #2021-1118 & UC IRB# 2022-0310).

Application thickness estimation

The data collected from the survey method was used to estimate a single sunscreen application thickness value per participant. The questions related to sunscreen application thickness were narrowed to the face and both arms. Instead of estimating sunscreen application to the entire body, it was thought that it would be easier for participants to separately consider and visualize specific application areas. Habits and practices of face sunscreen use have been changing in the past few years [ 15 ]; therefore, face application was one application area of interest. Application to both arms was included as a representative site for body application from the neck down.

The survey questionnaire was used to collect two key data points: (1) the amount of sunscreen typically applied to an individual’s face and both arms using a reference image and (2) each participant’s height and weight. These data were then combined to estimate each participant’s applied sunscreen amount and body surface area (BSA). Taken together, a face and body application thickness can be calculated (mg/cm 2 ).

Each participant was asked to review the reference image (Fig.  1 ) and indicate how much sunscreen they typically apply to their face and to both arms in two separate questions. In addition to a reference amount of sunscreen, common/easily recognizable food items were included in the reference image to further aid participants in estimating and recalling previous sunscreen applications. The amounts used in each picture were weighed prior to the survey and correspond to each food item: small candy = 0.75 g; blueberry = 1.25 g; almond = 2 g; raspberry = 5 g; and two grapes = 10 g. The height (recorded in feet and inches) and weight (recorded in pounds) of each individual participant were noted and were inputted into the BSA calculation from the United States Environmental Protection Agency’s (US EPA) equation [ 16 ], BSA = 0.0239 × (H^0.417) × (W^0.517). The resultant BSA value was calculated in centimeter squared for further analysis. The surface area of the participant’s face was estimated to be 5.5% of their total BSA (4.5% face plus 1% accounting for application with fingers) and both arms were estimated to be 18% of the participant’s total BSA [ 17 ].

Participants’ body weights were collected in 10-pound increments. The lower value in the weight range was used for the BSA range because this would provide the most conservative estimate of application thickness (i.e., amount applied to a smaller surface area gives a higher mg/cm 2 estimate). And while some participants might under-report their actual weight due to not being weighed recently or possible societal stigmas, using the lower value in the weight range results in a higher estimated application thickness amount. The conservative nature of the application thickness estimation adds a margin of safety when used in both environmental exposure estimates and possible human health exposure assessments.

Literature review

A literature review was conducted to serve as a test of validity of the survey results [ 18 ] and searched for all previously published studies quantifying sunscreen application thickness. A review of several websites using a set of keywords was used to identify a base set of papers. The initial search was conducted with Science Direct, PubMed, and Google Scholar using a combination of the following keywords: sunscreen application, sunscreen use/usage, consumer sunscreen application rate. Only papers published in English were searched.

Once the base set of papers was curated, inclusion and exclusion criteria were applied to identify the most relevant papers. Only those studies conducted with adults (>18 years old) were included. Studies that included measurements of the sunscreen application thickness to volunteers’ face and body were included. In addition, only studies that used lotion type products were included; therefore, studies measuring application of spray products, make-up, or lip products were excluded from the review. There were no geographic exclusion criteria.

After applying inclusion and exclusion criteria, a snowballing technique [ 19 ] was used on the core set of papers. For each paper, the text (forward snowballing) and the reference list (backward snowballing) were reviewed for further research to include in this literature review. Additionally, to ensure inclusion of the greatest number of relevant studies, the most frequently cited papers were selected for additional searching using Connected Papers ( https://www.connectedpapers.com/ ). This website connects publications based on their similarity and allows the identification of additional relevant publications.

Each paper was reviewed, and the reported application thickness amounts were collected along with the year of the study, details of the study population, geographic location, the method of measurement, and the study aim.

Statistical analysis

After each individual sunscreen application thickness was estimated, a logarithmic multiple variable regression analysis was conducted using IBM SPSS Statistics (version: 28.0.0.0 (190)) software to determine if any of the independent variables were significant predictors of sunscreen application thickness to the face or both arms. For this analysis, the statistical significance level used is 0.05. Non-numeric independent variables were transformed to numeric values (Table  S4 ). Summary statistics were also calculated for each data set using IBM SPSS Statistics.

The following sections summarize the history of published application thickness values since 1985 and the estimated application thickness values for sunscreen use on the face and body.

Semi-quantification of sunscreen application thickness to consumer’s face and arms

The questionnaire was in the field January 2022 and after Qualtrics removed incomplete and straight-lined (i.e., same response for each question) responses, a total of 9102 valid participant responses from the United States remained. Nearly 70% of respondents ( n  = 6325 of 9102 total) had used sunscreen at least once in the past 12 months (Table  S3 ). The data from the 6325 respondents that reported sunscreen use in the past 12 months were separated into two datasets: face application thickness and both arms application thickness. For each of these datasets, blank responses for that application site were removed along with any that responded “I typically don’t apply sunscreen to my face” or “I typically don’t apply sunscreen to my arms.” Next, in order to quickly identify incongruent height and weight combinations (e.g., 7’10” and 80 pounds), body mass index (BMI) [ 20 ] was estimated for each response and the dataset was sorted smallest to largest. The use of BMI as a filter to the dataset is not used to determine healthiness of the participants and was simply used to refine the current dataset recognizing the possibility of data entry errors. A BMI range of 14–40 (roughly equivalent to the 5th and 95th percentiles) was applied to each dataset as inclusion criteria for values falling within this range, resulting in 5399 responses for face application and 5203 responses for both arms application. The final filter applied to the data was removal of responses from individuals that did not use a lotion product in the last 12 months. The final dataset used to conduct the analysis is comprised of 4338 responses for face application and 3443 responses for both arms application.

The summary statistics for each dataset are listed in Table  1 . The mean value for the face application thickness for all respondents is 3.00 mg/cm 2 and 1.52 mg/cm 2 for the application thickness of both arms. The median values for face and arm application thickness are 1.78 mg/cm 2 and 1.35 mg/cm 2 , respectively. The range of values between the two datasets is also quite different. The dataset for face application thickness is highly skewed and has a large amount of variance. The mean and median values for the arm application thickness dataset are much closer in value when compared to the face application thickness value, further illustrating the skewness of the face dataset. Based on the frequency distributions, the median (1.78 mg/cm 2 ) of the face application dataset is likely more relevant whereas the mean (1.52 mg/cm 2 ) of the arms application dataset is the more relevant value. The application thickness results for both arms are more closely aligned with published values while the face application thickness dataset is quite different. Possible reasons for this difference will be discussed.

The initial histograms for application thickness illustrated a significant positive skew (Fig. S3 ); therefore, the application thickness values for both the face and arms were logarithmically (log 10 ) transformed before conducting logarithmic regression and additional statistical analysis. To determine which variables impacted application thickness on the face or arms, a multiple regression analysis of the log transformed values was conducted for each dataset. The variables included: state of residence, gender identity, age range, ethnicity, self-reported skin response to sun exposure (i.e., tendency to burn), Fitzpatrick skin type [ 21 ], reported history of skin cancer, the SPF range of the typical sunscreen used, if children are part of the household, use of sunscreen when planning to spend more than 30 min outdoors, use of sunscreen as part of their daily skincare routine, and residence in a warm or cold state (classified based on an average annual temperature from 1901–2000 above (warm) and below (cold) 50 °F [ 22 ]). For the log transformed face application thickness variable, the R 2 is 0.030 ( F (12, 4331) = 11.109, p  < 0.001) and for the log transformed arms application thickness the R 2 is 0.066 ( F (12, 3442) = 20.093, p  < 0.001; Tables  S5 and S6 ). The predictors that had statistical significance for the face application thickness variable were age ( p  = 0.004), ethnicity ( p  = 0.030), reported skin response to sun exposure ( p  < 0.001), reported history of skin cancer ( p  = 0.018), product SPF range used ( p  < 0.001) and the use of sunscreen in a regular skincare routine ( p  < 0.001). The predictors that had statistical significance for both arms application thickness variable were gender identity ( p  < 0.001), ethnicity ( p  = 0.045), Fitzpatrick skin type ( p  < 0.001), reported history of skin cancer ( p  = 0.020), and product SPF range used ( p  < 0.001).

In Table  2 , the significance of each independent variable to the dependent variable of application thickness is provided. For facial application thickness, age range has a negative correlation indicating younger sunscreen users will apply more sunscreen. There is a positive correlation of ethnicity to application thickness but no valuable interpretation can be gained from this due to the fact that ethnicity is not a scaled variable. A person’s tendency to burn (skin response to sun exposure) is negatively correlated with thickness application meaning those that tend to burn more will apply a greater amount of sunscreen to their face. The same can be said of those with a self-reported history of skin cancer and those that regularly use a sunscreen product as part of their skincare routine. The product SPF range used by participants is positively correlated to facial application thickness meaning those that use a higher SPF product tend to apply more sunscreen per application. For application to both arms (i.e., body), gender identity is negatively correlated to application thickness suggesting women typically apply a greater amount of sunscreen to their body. Both Fitzpatrick skin type and history of skin cancer are negatively correlated to application thickness. Those with lighter skin tone and/or a history of skin cancer apply a greater amount of sunscreen to their body. Like facial application, product SPF range is positively correlated to application thickness indicating the higher product SPF used then the more sunscreen is generally applied. Again, ethnicity is positively correlated but no interpretation can be made based on these results.

The second survey was in the field during May 2022 and resulted in a sample size of 2192 participants. Though some refinement of the dataset was achieved, the results for the follow-up survey had very similar results as the first study (see Table  1 ). For facial sunscreen application thickness, the dataset was still highly skewed (skewness = 1.888) and had significant variability (range: 0.39–14.33 mg/cm 2 ; variance: 6.723). The second survey asked participants if they apply a greater amount of sunscreen to their face compared to their body (Fig. S4 ). Participants agreed strongly or somewhat agreed that they apply a greater amount of sunscreen to their face (69%).

Previously reported application thickness

The literature review search criteria initially identified 43 papers related to sunscreen application. After the inclusion and exclusion criteria was applied (quantified lotion sunscreen application thickness to the body and/or face in adult volunteers), 25 publications measuring sunscreen application thickness were included in the review. Each paper was reviewed, and data were extracted into summary Table  S2 . It should be noted that a critical review of each study’s method of measuring application thickness was not conducted; instead, results are reported as published. In total, 39 values of application thickness were identified from the 25 studies that were conducted around the world (Fig. S1 ). Only four studies reported sunscreen application thickness to the face. The majority of studies measured and reported values for the whole body, including the head.

All reported values are collated in Fig.  2 and cover the years 1985–2020. The data were not consistently reported in the literature with summary statistics including a mixture of mean and median values for application amounts. For the years 1985–2017, 14 reported median values ranged from 0.2 to 2.4 mg/cm 2 [ 11 , 23 ]. For the years 1992–2020, 25 reported mean values ranged from 0.46 to 5 mg/cm 2 [ 24 , 25 ]. The red line in Fig.  2 represents the US FDA’s recommended application thickness (2 mg/cm 2 ). This figure illustrates how consumers have consistently applied an inadequate amount of sunscreen over the years. Petersen and Wulf [ 12 ] conducted a review of sunscreen application thickness and also observed the lower sunscreen application amount versus authority recommendations. They stated, “there is a discrepancy between the amount of sunscreen applied during testing and in reality”. Of note, two values from a 2020 study [ 24 ] were above the FDA-recommended application thickness and were obtained from volunteers with a history of skin cancer applying sunscreen to their face. This confounding variable likely accounts for higher use compared to other sub-populations.

The figure includes the published application thickness values (mean - blue solid bar, median black and white striped bar) that have been reported in the literature (1985–2020).

The literature review also summarized the methods employed to measure sunscreen application thickness from all the reviewed studies. Five measuring techniques are identified along with their respective percentage use in determining the 39 reported application thickness measurements (Fig. S2 ). The most common technique was to simply weigh the sunscreen product before and after application to determine the amount applied. Then, the investigators estimated the application surface area using different BSA calculation methods [ 17 , 26 , 27 ]. Additional methods such as tape stripping [ 11 , 28 ], skin swabbing [ 29 ], and fluorescence dose-response [ 30 , 31 ] have been investigated to determine application thickness but have not been widely adopted based on the results of this literature review.

The results of this research illustrate how a large-scale online consumer survey can be used successfully to collect data for consumer application of sunscreen products. The estimated sunscreen application thickness for both the participants’ arms (mean = 1.52 mg/cm 2 ; median = 1.35 mg/cm 2 ) is greater than several of the measured values reported in the literature (mean range 0.46–5 mg/cm 2 ; median range 0.2–2.4 mg/cm 2 ); however, both values are still below the US FDA recommended application thickness of 2 mg/cm 2 . In addition, the observed variability of the application thickness to both arms from this research also reflects a similar range as compared to the historical data set (this study: 0.15–4.94 mg/cm 2 and literature review results: 0.2–5 mg/cm 2 [ 11 , 24 ]). For body estimates of sunscreen application, the method designed for this study is a viable option to reach a large population of sunscreen users.

As stated previously, the US FDA recommended application thickness is typically used in exposure models to account for consumer use and provide some level of conservativeness in the assessment. But to move toward more realistic environmental exposure assessments that can better inform risk management decisions, refinement of UV filter environmental emissions is needed. The NASEM report states “models of the environmental impact of UV filters that rely on currently recommended doses of sunscreen likely overestimate environmental outcomes and would be considered upper bounds [ 13 ].” While the US FDA recommended application thickness of 2 mg/cm 2 does not appear to be vastly different than the current mean value of 1.52 mg/cm 2 (both arms application thickness) from this study, the significance can be demonstrated with a simple exposure model. For this example Waikiki beach in Honolulu County, Hawaii will be used. In 2021, the beach received 9,284,101 visitors ( https://emergencyservices.honolulu.gov/ ). Using this data, plus several additional assumptions, the total possible sunscreen emission to the aquatic environment can be roughly estimated and compared. Assuming the annual visitation is evenly distributed for each day (25,463 per diem), 70% of the visitors apply sunscreen (this research), 50% of the beach visitors enter the water (conservative assumption), 75% of each person’s body is covered with sunscreen (conservative assumption), 24% [ 32 ] of the UV filter is rinsed off the body, and the average body surface area is 18,352.59 cm 2 (this research), the potential direct release of sunscreen from a single application can be calculated. For the worst-case scenario of the US FDA recommended application of 2 mg/cm 2 , up to 59 kilograms of sunscreen may end up in the environment at Waikiki beach per day. However, using the data from this research, up to 45 kilograms of sunscreen may end up in the environment at Waikiki beach per day, nearly 24% less than the upper bound value. Comparing these two results illustrates the value of refining conservative emissions assessments and the relevance of consumer sunscreen usage research. There are two important points to note. First, these are very conservative assumptions used for illustrative purposes only and are not assessments that should be used in any type of environmental risk assessment or to inform risk management decisions. This example does not include the environmental fate of the target chemicals nor any type of degradation. Second, this is total sunscreen mass from a single application and does not account for the UV filter formula composition or differences in reapplication thickness.

Further refinement and consumer research is needed to make this method more reliable for estimated sunscreen application thickness to the face. The dataset for face application thickness is positively skewed (skewness: 1.79) and has a large amount of variability (range: 0.52–15.38 mg/cm 2 ; variance: 8.385). The sunscreen market is growing and evolving beyond only sunscreen products designed for use at the beach. The market now includes multi-functional products designed with SPF protection and products designed for daily sun protection [ 33 ]. The survey conducted for this research did not distinguish between lotion products designed for beach use (traditional sunscreen) and those designed for daily/routine sun protection when asking participants about their sunscreen application amounts. With this change in consumer habits and practices since the US FDA OTC Sunscreen monograph was published in 1972, further studies are needed to understand both the frequency of use and the amount of sunscreen applied and reapplied to the face.

The results of the literature review indicate that consumers historically have not applied adequate amounts of sunscreen lotion to achieve the labeled sun protection factor. And while the general trend is toward increasing application amounts over time, there is not a way to measure the significance of the trend due to the differences in the reported measurement methods and data analysis. Anecdotally, this increasing trend may be evidenced in the rising prominence of online skincare influencers and the continued growing sunscreen market [ 15 ].

Due to the COVID pandemic, survey participants may not be going to the beach as frequently as they typically would and may not have an accurate recollection of their typical sunscreen use. Similarly, these questionnaires rely on self-reporting which has limits on obtaining the most accurate data. Also, the results from this research are semi-quantitative and not an exact measure of sunscreen application amounts which limits the distribution of the results. Respondents may have also misread the application amount question and answered it as the amount they apply for the entire day instead of a single application. The combination of these conditions may lead to a greater amount of uncertainty compared to more controlled sunscreen application studies that have been conducted in the past. Nonetheless, results in this study are supported by previous work showing similar trends for body application thickness.

Despite the potential increased uncertainty in the data, they still provide new value when attempting to determine the impacts of different UV filters on the environment and human health. For sunscreen application to the body, the current research dataset and the historical data reveal consumers are not applying the recommended amount of sunscreen. Therefore, using 2 mg/cm 2 as an assumed application thickness in any UV filter exposure and/or risk assessment (such as the maximal usage trial (MUsT) as executed and required by US FDA [ 34 , 35 ]) is likely to yield an overestimate of exposure. Therefore, data and insights from this research can be used to ground truth current human health exposure and risk assessments related to UV filters and other sunscreen ingredients for both beach and routine daily sun protection products. Employing more realistic sunscreen usage estimates can also better inform co-exposure assessments since many sunscreens contain more than one UV filter per product and UV filters are found in other personal care products.

These insights can also be used to improve recommendations and education campaigns around safe sun exposure. Skin cancer is the most diagnosed cancer in the US [ 13 ]. In 2019, the incidence of skin cancer was six times higher than it was 40 years ago, which is out of proportion when compared to other types of preventable cancers [ 13 ]. In 2013, 39.5 million Americans sought medical care due to sun-related skin damage resulting in a cost of $1.8 billion [ 36 ]. The NASEM report found the “consistent use of broad spectrum, SPF 30 sunscreen when outdoors reduces the risk of developing skin cancer (keratinocyte carcinomas and melanomas), photoaging, and sunburn.” As this research illustrates, many people are not applying adequate sunscreen to ensure protection from the harmful effects of chronic sun exposure and the burden of these effects has been increasing over the years. Thus, when conducting environmental risk assessments of UV filters, the importance of sunscreen use to human health cannot be ignored. Replacing overly conservative assumptions with more accurate value that represent current consumer sunscreen use will result in more realistic exposure and risk assessments and lead to better informed and balanced risk management actions for both human and environmental health.

The survey and questionnaires for this research were specifically designed to test the use of an online platform to estimate sunscreen application thickness. The results illustrate the success of this method. However, the current study design needs additional refinement to clarify specific independent variables that predict sunscreen application thickness and to what extent the variables influence the application thickness of different sub-populations. Furthermore, the visual reference should be updated for facial sunscreen application. Using such large amounts for a small area of the body may contribute to the large range and possible misunderstanding on the part of the participants. Further research is also needed to develop a better understanding of consumer facial and body sunscreen reapplication thickness and frequency.

In the end, this study demonstrates that there are many factors influencing an individual’s sunscreen usage. The results of this study confirm that the general population does not apply the recommended amount of sunscreen to the body. Consumers who apply sunscreen to their face apply a greater amount than previously anticipated. These data can be used to refine risk assessments of UV filters applied to the body and directly enter the environment at the beach, but further work is needed to improve ERAs for UV filters in facial sunscreen products.

Data availability

All data used in this study analysis are available as a Microsoft Excel file in the  Supplementary Information accompanying this paper.

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Acknowledgements

The authors would like to thank Dr. Marty Visscher (University of Cincinnati) for providing guidance and expert opinion during the IRB submission and approval process. The authors would also like to thank Sharon Struewing (Kao USA Inc) and Liz Bangs (formerly Kao USA Inc) for their guidance and expert opinions on the questionnaire design and survey field placement.

This research was funded by Kao USA Inc. in support of the corresponding author’s employer sponsored PhD research project at the University of Cincinnati, James L. Winkle College of Pharmacy. This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

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AMC: conceptualization, methodology, formal analysis, investigation, data curation, writing—original draft, visualization. JCC II: data interpretation, writing—original draft and review and editing. JJG: data interpretation. HK: writing—review and editing.

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Carrao, A.M., Coleman, J.C., Guo, J.J. et al. A novel online survey approach designed to measure consumer sunscreen application thickness—implications for estimating environmental emissions. J Expo Sci Environ Epidemiol (2023). https://doi.org/10.1038/s41370-023-00608-z

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Received : 22 November 2022

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Published : 28 October 2023

DOI : https://doi.org/10.1038/s41370-023-00608-z

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Science Challenge: Summer Sunscreen Experiment

Have you been wearing your sunscreen?  On a sunny day, see what kind of protection sunscreen offers with this easy experiment.

Black construction paper Sunscreen (lotion, not spray – minimum SPF 30)

• Fold the paper in half.
• Spread sunscreen on one side of the paper, but not the other.  Make a design if you like!
• Leave the paper in a sunny spot for a few hours.
• Observe the differences between the two sides of the paper.  Is the side with the sunscreen still dark?  What about the other side?

Keep the Experiment Going and Real World Application

If you have sunscreens of different SPF, test them out at the same time.

SPF stands for sun protection factor.  The sun emits ultraviolet (UV) light, which is invisible to our eyes and has higher energy than visible light.  Exposure to UV radiation causes sunburn, but sunscreen protects from UV rays.  The higher the SPF, the greater the protection.  The SPF is determined experimentally indoors by exposing human subjects, some wearing sunscreen and some not, to a light spectrum meant to mimic noontime sun.  The amount of light that induces redness in sunscreen-protected skin divided by the amount of light that induces redness in unprotected skin is the SPF.  For instance, SPF 15 sunscreen delays the onset of a sunburn in a person who would otherwise burn in 10 minutes to burn in 150 minutes.

Sources: PBS Sciencebuddies Dermatology. About.com

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Home > EVENTS > SCJAS > 2016 > All > 207

The Effect Of Various Sunscreens On Uv Sensitive Yeast

Emmye Mullins Amelia Robinson Brown

School Name

Heathwood Hall Episcopal School

Grade Level

Presentation topic.

Consumer Science

Presentation Type

Non-Mentored

The purpose of this experiment was to determine the effectiveness of various sunscreen brands to protect yeast cells against UV radiation. Yeast cells were chosen because they are a good model of human cells. UV sensitive yeast (Saccharomyces cerevisiae) were grown on Petri dishes. Then different sunscreen brands: Banana Boat, Coppertone, Hawaiian Tropic, and Neutrogena were applied to plastic wrap and placed over different Petri dishes. The Petri dishes were exposed to UV radiation for one hour with one half of each Petri dish exposed and the other half covered with aluminum foil. Petri dishes were photographed and then using ImageJ software, the average pixel color intensity in candelas per square meter of the exposed side was compared to the covered side. These numbers were used to find the percent of yeast cells lost in each Petri dish. It was hypothesized that if the Coppertone Clearly Sheer For Sunny Days Sunscreen Lotion SPF 30 is applied to the UV sensitive yeast cells, then it will protect the cells more than the other brands of sunscreen because it contains the highest percentage of active ingredients. The null hypothesis was that the brand of sunscreen would have no effect on the protection of yeast cells against UV radiation. Neither of these hypotheses were supported by the data. Instead, the data showed that Hawaiian Tropic best protected the yeast cells from UV radiation.

Recommended Citation

Mullins, Emmye and Robinson Brown, Amelia, "The Effect Of Various Sunscreens On Uv Sensitive Yeast" (2016). South Carolina Junior Academy of Science . 207. https://scholarexchange.furman.edu/scjas/2016/all/207

4-16-2016 9:30 AM

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FREE K-12 standards-aligned STEM

curriculum for educators everywhere!

Find more at TeachEngineering.org .

• TeachEngineering
• How Effective Is Your Sunscreen?

Hands-on Activity How Effective Is Your Sunscreen?

Grade Level: 11 (10-12)

(two 60-minute class periods)

This activity also uses some non-expendable (reusable) items, such as UV sensors; see the Materials List for details.

Group Size: 3

Activity Dependency: Electromagnetic Radiation Flame Test: Red, Green, Blue, Violet? Skin and the Effects of Ultraviolet Radiation

Subject Areas: Biology, Chemistry

NGSS Performance Expectations:

Curriculum in this Unit Units serve as guides to a particular content or subject area. Nested under units are lessons (in purple) and hands-on activities (in blue). Note that not all lessons and activities will exist under a unit, and instead may exist as "standalone" curriculum.

• Flame Test: Red, Green, Blue, Violet?
• Nanotechnology Grant Proposal Writing

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Engineering connection, learning objectives, materials list, worksheets and attachments, more curriculum like this, introduction/motivation, user comments & tips.

This activity provides students with a lab experience in engineering design for quality control. Also, by working in groups, students learn to acknowledge and implement ideas from all members, much like engineers do in industry. The activity also includes chemical and environmental engineering connections—examining the chemical reactions that are involved when chlorofluorocarbons react to break down the ozone layer and the implications to overall public health when pollution causes this to occur, as well as laboratory-based experimentation as part of the design of new products and processes.

After this activity, students should be able to:

• Explain how to conduct a quality control experimental design.
• Describe how UVA and UVB sensors can be used to measure UV intensity.
• Design a controlled one-variable experiment.
• Test and evaluate previously determined experimental values.

Educational Standards Each TeachEngineering lesson or activity is correlated to one or more K-12 science, technology, engineering or math (STEM) educational standards. All 100,000+ K-12 STEM standards covered in TeachEngineering are collected, maintained and packaged by the Achievement Standards Network (ASN) , a project of D2L (www.achievementstandards.org). In the ASN, standards are hierarchically structured: first by source; e.g. , by state; within source by type; e.g. , science or mathematics; within type by subtype, then by grade, etc .

Ngss: next generation science standards - science.

Common Core State Standards - Math

View aligned curriculum

Do you agree with this alignment? Thanks for your feedback!

International Technology and Engineering Educators Association - Technology

State standards, tennessee - math, tennessee - science.

Each student needs:

To share with the entire class:

• sunscreen SPF 15
• sunscreen SPF 45
• sunscreen containing zinc oxide nanoparticles
• sunglasses, either ask groups that want to use sunglasses in their designed experiments to bring in sunglasses from home, or else purchase some inexpensive ones, such as https://www.qualitylogoproducts.com/tradeshow-promotions/sunglases.htm?variant=BLANK&imageID=262438&gclid=CNWLrKGq68ACFQiIaQodikAAoA
• UV sensitive beads, such as a package of 240 ultraviolet-detecting beads from Flinn Scientific at https://www.flinnsci.com/ultraviolet-detecting-beads/fb1147/
• UV intensity meter and lens tester card, at https://www.flinnsci.com/uv-intensity-meter-and-lens-tester/ap6412/
• plastic bags
• plastic wrap
• UV lamp, such as https://www.flinnsci.com/ultraviolet-lamp-hand-held/ap1901/  
• Vernier UVA sensor, such as https://www.vernier.com/products/sensors/uv-sensors/uva-bta/
• Vernier UVB sensors, such as https://www.vernier.com/products/sensors/uv-sensors/uvb-bta/  
• access to the outdoors

In this activity, we will look at different forms of skin protection from ultraviolet light. Your challenge is to design a quality control experiment to test the protective substances. You will build on what you have learned in the previous lesson by taking a closer look at ultraviolet radiation and how the overexposure of UV radiation can have detrimental effects to humans' overall health.

We have been looking at how UV radiation can cause several types of skin cancer. Today we are going to quality control test some products with various sun protection factors (SPFs) including one that uses zinc oxide nanoparticles as a protection factor.

The skin is the body's first defense against all outside intrusion. Designing ways to protect against and detect skin cancer is one of the current focuses of biomedical engineers. Understanding, measuring and mitigating the pollution-caused deterioration of the ozone layer is another concern for engineers, because of the impact of increased UV radiation on the incidence of skin cancer. Biomedical and chemical engineers work with physicians to design and test medicines, new products and medical technologies.

Refer to the UV Radiation Designed Experiment Lab Handout for additional guidance and support for this activity. Have students complete the lab handout as they design and conduct their labs. Refer to the Lab Handout Answers and Rubric for suggested grading components.

Expect students' experimental designs and results to vary since the objective is for teams to design their own experiments. Make available a selection of items as suggested in the Materials List, so that groups have a variety of options. For example, students can use any of the provided sunscreens or sunblock, plastic bags or plastic wrap, sunglasses—as items that can filter/block/protect against UV radiation—and select a UV detector—the intensity meter and lens tester card, the UV sensitive beads or the UVA/UVB sensors. For an ultraviolet light source, they can use sunlight (if available) or the UV lamp. The intent is to mirror the controlled tests that are performed during engineering research and experimentation—to test one variable in a design at a time.

UV-sensitive beads change to random colors when exposed to UV light of either UVA or UVB wavelengths. Sunscreen will not adhere directly to the bead surface, so students must come up with ways to contain the beads in something transparent that will have minimal UV absorption, and then apply the sunscreen to that material.

For quantitative results, a UVA and UVB sensor is recommended. These can be purchased from Vernier or another scientific supply company. If probes are used, or whenever quantitative data is obtained, require students to include a graph in the data and analysis section of the lab report.

Before the Activity

• Gather materials and make copies of the UV Radiation Designed Experiment Lab Handout , one per student.
• Set out the supplies so groups may examine and choose experiment materials.

With the Students

• Divide the class into groups of three students each. Present the engineering challenge: To design a controlled experiment to quality test the effectiveness of one aspect of current UV safety products.
• Direct students to choose from the given materials to design their experiments. If a group brainstorms additional materials that would aid in its design, have the group make a request to the instructor to obtain approval.
• Make sure students understand that this must be a one-variable (chosen by the group) controlled experiment.
• Have each student group explain its designed experiment to the teacher for approval. If the teacher identifies any problems with the experiment, have students revise the experiment and meet with the teacher again for approval.
• Once approved, have student groups conduct their experiments and gather data. If a design uses the UVA and UVB sensors, have students collect quantitative data; otherwise, students' data may be recording whether UV sensor beads change color or not, or whether the UV intensity meter and lens tester card indicates "low," "medium" or "high" UV. Whenever possible, expect students to produce graphs of their collected data to include in lab reports and presentations.
• Require each student to complete his or her own lab report with results typed and presented the following day. Require the following report sections: title, purpose, materials, procedure (designed by the students), data and analysis, and conclusion (which must tie back to the purpose). A grading rubric is provided on the lab handout.
• On the following day, have student groups discuss their lab reports, including the graphs that they created and conclusions that were drawn. Let each group decide specifically what information to prepare to present to the class.
• Have each group present a summary explanation of its designed experiment to the class, covering all the required sections of the lab report.

Pre-Activity Assessment

Pre-Lab Questions : Have students complete the pre-lab questions on the UV Radiation Designed Experiment Lab Handout , which provides a review of information taught in the associated lesson. If available, permit students to conduct research online. Gauge students' base level of knowledge as you review the answers together as a class and let students correct any incorrect answers.

Activity Embedded Assessment

Experimental Lab Design: In small groups, have students brainstorm and design experiments to test one variable. As part of each team's unique experiment design, have students select appropriate materials, write a full procedure, and once approved, conduct the experiment and gather data. Refer to the lab report grading rubric in the Lab Handout Answers and Rubric.

Post-Activity Assessment

Lab Reports & Presentations: Require students to individually turn in typed lab reports that summarize their group-designed experiments. Require the following sections: title, purpose, materials, procedure (designed by the students), data and analysis, and conclusion (which ties back to the purpose). The following day, have teams present their experiments and results to the class, recapping the report sections.

After seeing ultraviolet-sensitive beads change color and learning how they work, students learn about skin anatomy and the effects of ultraviolet radiation on human skin, pollution's damaging effect on the ozone layer that can lead to increases in skin cancer, the UV index, types of skin cancer, AB...

Students learn about the electromagnetic spectrum, ultraviolet radiation (including UVA, UVB and UVC rays), photon energy, the relationship between wave frequency and energy (c = λν), as well as about the Earth's ozone-layer protection and that nanoparticles are being used for medical applications

Students learn how to prevent exposure to the sun's ultraviolet rays. Students systematically test various sunscreens to determine the relationship between SPF (sun protection factor) value and sun exposure.

This unit on nanoparticles engages students with a hypothetical Grand Challenge Question that asks about the skin cancer risk for someone living in Australia, given the local UV index and the condition of the region's ozone layer. Through three lessons, students learn about the science of electromag...

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How Effective Is Your Sunscreen?

In this video, two boys who spend lots of time outdoors, test which level of sunscreen best protects their skin from the harmful effects of the sun's rays. The boys order a set of special water bottles designed to change color when exposed to ultraviolet rays. They then apply olive oil, shortening, and three sunscreens of different sun protection factors (SPFs) to the bottles and gauge how well they work.

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LAB in Radiation , Electromagnetic Spectrum , Radiation , Unlocked Resources . Last updated December 14, 2023.

In this lab, students will research and compare the effectiveness of various SPF levels in sunscreen lotions. The lotion’s ability to block UV (ultraviolet) radiation from the sun will be tested using a UV bead detector.

Grade Level

Middle or high school

NGSS Alignment

This lab will help prepare your students to meet the performance expectations in the following standards:

• MS-PS3-5: Construct, use, and present arguments to support the claim that when the kinetic energy of an object changes, energy is transferred to or from the object.
• HS-PS4-4: Evaluate the validity and reliability of claims in published materials of the effects that different frequencies of electromagnetic radiation have when absorbed by matter.
• Analyzing and Interpreting Data
• Engaging in Argument from Evidence

By the end of this lab, students should be able to

• determine the effectiveness of sunscreen lotions in blocking the sun's UV radiation.
• evaluate the amount of UV-A penetration when using sunscreens with different SPF.

Chemistry Topics

• Electromagnetic Spectrum

Teacher Preparation : 20 minutes

Lesson : 60 minutes

• UV light detector beads (many online purchase options)
• Multiple types of sunscreen, with various SPF ratings
• 1 box of clear, quart-sized sealable bags
• Do not look directly at the sun while using the UV detector as it may cause permanent eye damage, nor stay exposed to the sun's ray for a prolonged time period.
• Remind the students NOT to consume any of the material.
• Students should wash their hands thoroughly before leaving the lab.
• When students complete the experiment, instruct them how to clean up their materials and dispose of any chemicals.

Teacher Notes

• For best results, plan to conduct this experiment on a bright sunny day.
• During preparation you should put the sunscreen into smaller, labeled containers for each group, rather than having to distribute all of it at the time of experiment.
• Have students complete the Research Questions prior to starting the investigation. It could be on the same day, or a day prior to this, depending on available time.
• Everyday Mysteries: How does sunscreen work?
• About Education: How does sunscreen work?

Cross-Disciplinary Extensions

Connect to Math Students will be recording the data they’ve collected in multiple ways of expression—tables, graphs, etc.

Connect to Reading Students will be reading research information on the effects of sunscreen on your skin and how the UV radiation is blocked through various levels of SPF.

Connect to Writing Students will be answering multiple focus questions in written form throughout this investigation.  They will also be recording data in multiple mediums.

Connect to Social Studies Students will be able to apply their findings to real-world applications in their daily lives, as well as the lives of others around the world.

For the Student

Sunscreen works by combining organic and inorganic active ingredients. Inorganic ingredients reflect or scatter ultraviolet (UV) radiation. Organic ingredients absorb UV radiation, dissipating it as heat. Some sunscreens protect us from the two types of damaging UV radiation: UV-A and UV-B. Both UV-A and UV-B cause sunburns and damaging effects such as skin cancer.

To research and compare the effectiveness of various SPF levels in sunscreen lotions for blocking UV (ultraviolet) radiation from the Sun using a UV Bead Detector.

• UV light detector beads
• Complete the Research Questions prior to starting the investigation.
• Create an appropriate data table similar to the one shown to collect your data. Use the terms "White," "Light blue," "Medium blue," or "Intense or dark blue" when recording the UV-bead color intensity.
• Place the UV-Detector inside of a clear plastic bag and seal. Make sure that only the plastic is between the sun and the detector.
• In the data table, record the color intensity reading shown on the scale. This is the control reading, and will be a baseline to compare the other readings to see if they increase or decrease.
• Apply a uniform layer of the first sunscreen sample over the bag. Make sure the bag is thoroughly covered. Allow the lotion to dry.
• Place the bag in direct sunlight.
• Wait 10 minutes to allow the detector beads to change color. Record the SPF value of the sunscreen and any color change in the data table.
• Remove the UV-Detector from the bag.
• Place the detector in area where it will not receive sunlight until the beads turn back to white.
• Place the UV-Detector inside of another clear plastic bag and seal.
• Repeat steps 3-9 for each different sunscreen sample.
• For a scientifically accurate investigation the entire processed should be conducted at least 3 times.
• Calculate the average UV reduction (if any) for each sunscreen.

Using the data in the table, plot a bar graph with SPF Value along the x-axis and the UV Penetrating Intensity Level along the y-axis.

Research Questions

• What is the difference between UV-A and UV-B radiation?
• Why is prolonged exposure to ultraviolet radiation harmful to the eyes and skin?
• What protection from UV radiation should an effective sunscreen offer?
• What does a sunscreen's "SPF" rating mean?
• Does SPF tell how well a product blocks UV-A or UV-B?
• How does sunscreen differ from sunblock?
• Which sunscreen is most effective at blocking UV light?
• Are the experimental results consistent with the SPF rating for each sunscreen tested?
• What safety features are designed into the UV Light Detector?
• Does SPF 30 have twice as much protection as SPF 15?
• What reduces the effectiveness of sunscreen?
• What should one look for when buying sunscreen?

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Article Contents

S ubjects and m ethods, d iscussion.

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Sunscreen Use and Duration of Sun Exposure: a Double-Blind, Randomized Trial

• Article contents
• Figures & tables
• Supplementary Data

Philippe Autier, Jean-François Doré, Sylvie Négrier, Danièle Liénard, Renato Panizzon, Ferdy J. Lejeune, David Guggisberg, Alexander M. M. Eggermont, For the European Organization for Research and Treatment of Cancer Melanoma Group, Sunscreen Use and Duration of Sun Exposure: a Double-Blind, Randomized Trial, JNCI: Journal of the National Cancer Institute , Volume 91, Issue 15, 4 August 1999, Pages 1304–1309, https://doi.org/10.1093/jnci/91.15.1304

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BACKGROUND: In epidemiologic studies, sunscreen use is associated with increased risk of cutaneous melanoma, basal cell skin cancer, and higher numbers of nevi. It has been proposed that sunscreens may encourage prolonged sun exposure because they delay sunburn occurrence. We examined whether, under habitual conditions of sunscreen use, the sun-protection factor (SPF) had an influence on sun-exposure duration. METHODS: Before the 1997 summer holidays, we randomly assigned 87 French and Swiss participants who were 18-24 years of age to receive an SPF 10 or an SPF 30 sunscreen. Neither medical personnel nor study participants were aware of their sunscreen assignment. Participants were asked to complete daily records of their sun exposure. To avoid influencing the recreational sun-exposure habits of the study participants, no recommendation was made about sun exposure or sun protection. Furthermore, participants were told that the trial end point was the number of pigmented skin lesions before and after the holidays. One subject was lost to follow-up. All statistical tests were two-sided. RESULTS: The SPF 10 (n = 44) and SPF 30 (n = 42) groups had equivalent mean holiday durations (19.4 days versus 20.2 days) and mean quantities of sunscreen used (72.3 g versus 71.6 g). The mean cumulative sun exposures for the two groups were 58.2 hours and 72.6 hours, respectively ( P = .011). The mean daily durations of sunbathing were 2.6 and 3.1 hours, respectively ( P = .0013), and, for outdoor activities, they were 3.6 and 3.8 hours, respectively ( P = .62). There was no difference in sunburn experience between the two groups. CONCLUSIONS: Use of higher SPF sunscreen seems to increase the duration of recreational sun exposure of young white Europeans.

Sun exposure is believed to be the main environmental determinant of skin cancers ( 1 ), and sunburn experience is associated with skin cancer occurrence ( 2 ). Sunscreens are able to delay sunburns and to reduce some UV-induced skin lesions, such as nonmelanoma tumors in rodents, local immunologic depression, mutations of the p53 (also known as TP53) gene in keratinocytes, and the incidence of actinic keratoses in humans ( 2 - 7 ). As a consequence, sunscreen use has become recommended as a sun-protection method, and that protection is deemed to increase with increasing sun-protection factor (SPF). The SPF indicates the ability of a sunscreen to delay the skin erythemal reaction induced by the solar radiation.

In contrast to the results of experimental studies, observational studies have repeatedly found sunscreen use to be associated with higher risk of cutaneous melanoma and basal cell skin cancer and with higher counts of nevi ( 8 - 16 ). By way of explaining this difference, it has been hypothesized that, because they delay sunburn occurrence, sunscreens could allow prolonged sun exposure, a situation that could lead to increased skin cancer risk ( 1 , 9 ).

If the hypothesis that sunscreen use encourages longer sun exposure is correct, then higher SPF should lead to greater sun-exposure duration ( 17 ). We conducted a two-center, double-blind, randomized study to determine whether, in the habitual conditions of sunscreen use by European young adults, the SPF had an influence on duration of sun exposure.

Study Subjects

Study subjects were healthy, paid volunteers 18-24 years old recruited in universities in Lyon (France) and Lausanne (Switzerland) and from nonmedical disciplines. Participants had to have a positive history of sunburn in the past and to be regular sunscreen users intending to have at least 15 days of holidays in sunny areas during the next 2 months. Volunteers with a current skin disease, even minor, or who had a history of a skin disease that lasted for 1 year or more were not eligible. Pregnant women, subjects with a chronic physical illness, or subjects taking a photosensitizing medication were also ineligible.

Participants were randomly assigned to receive an SPF 10 or an SPF 30 sunscreen. The two sunscreens used in this study were broad spectrum, commercially available, high-quality preparations from the same brand. The two sunscreens were prepared with the same chemical absorbents and mineral-oxide reflectants active in the UV A and B wavelengths, but the SPF 30 sunscreen contained a higher concentration of these substances. Both sunscreens had the same appearance, fragrance, color, and texture. They were bought from a local retailer and repackaged in unidentifiable tubes. Five tubes of 60 mL per participant were prepared by an experienced pharmacist (average, 373-g gross weight).

The study was conducted in accordance with the principles of the Helsinki declaration and was submitted for approval to an Ethical Review Committee of the Centre Léon Bérard (Lyon) and of the Centre Hospitalier Universitaire Vaudois (Lausanne). Each participant signed a written informed consent before randomization.

Study Design

The trial design is shown in Fig. 1. The study end point was the duration of recreational sun exposure. Recreational sun exposure included sunbathing and other outdoor activities, such as walking, playing, and enjoying sport (e.g., swimming or boating) in the sun. To avoid the possibility that knowledge of the actual end point could influence sun-exposure behavior, the stated study end point for participants and all persons in contact with them was the influence of different types of sunscreens on pigmented lesions of the skin. Since nevus counting and the assessment of the freckling index merely served to distract subjects from the real study objective, data on pigmented skin lesions are not presented.

Data from a 1992 survey in Connecticut ( 18 ) suggested a difference of 0.33 hour in daily sun exposure (standard deviation of 2 hours) between sunscreen users and nonusers. Assuming an average of 10 days with sun exposure per participant, to detect a 0.33-hour difference in daily sun exposure, with 90% power and a two-sided alpha error of 5%, at least 80 subjects had to be included.

A person who had no contact with the participants or the medical personnel involved in the study performed the randomization on an individual basis. By use of a table of random numbers, a five-digit random number was assigned to each set of five sunscreen tubes. Next the sets were ordered by successive random numbers.

Potential participants were invited to attend a medical examination. Following eligibility checking, the freckling index (face, arms, and shoulders) was assessed and the numbers of nevi were counted on both arms and on the back. A photograph of the back was also taken. Randomized sets of five sunscreen tubes were given to participants on a consecutive basis. To keep the trial close to participants' habitual conditions of recreational sun exposure, no recommendation was made either about sun exposure or about sunscreen use. Participants were asked to complete a standard daily diary recording detailed data on their sun exposure: hours and type of sun exposure (e.g., sunbathing, swimming, and boating), amount of clothing (e.g., nude, naked breasts, and one- or two-piece swimming suit), number of sunscreen applications, time of application (i.e., before or after starting sun exposure), and sunburn or skin-reddening experience (sunburn was defined as an episode of painful skin erythema; skin reddening was defined as an episode of painless skin erythema). If another sunscreen was used, the participant was asked to record the day and time of day the other sunscreen was used, the commercial name, the SPF, and the motive for changing to another product.

In September, the participants attended a second medical examination during which all sunscreen tubes were taken back and weighed. The daily diaries were collected and verified for completeness. In case there were missing data, the participants were directly asked to provide the missing information during that second medical examination. Participants also completed a questionnaire on their lifetime sun-exposure habits, sunburn experience, and sunscreen use. Their skin phototype was determined according to their propensity to sunburn or to get a tan when going unprotected in the mid-day sun ( 19 ): The skin phototype I subject always burns and never tans, the skin phototype II subject always burns first and tans after, and the skin phototype III subject sometimes burns but always gets a deep tan. In this study, there were no skin type IV subjects, i.e., subjects who never burn and always get a deep tan.

Statistical Analysis

Sun-exposure durations were calculated from the daily record diaries. Missing or imprecise data on sun-exposure hours remained for 5 (0.4%) of the 1312 days with sun exposure. Sun exposures during these 5 days could thus not be included in the calculations of sun-exposure duration. After data entry, the randomization code was broken and the analysis was performed. Student's t test, the uncorrected χ 2 , and the Wilcoxon rank sum test were used for testing univariate statistical associations. Least-squares regression multivariate analysis was used to assess the influence of different factors on study end point. All statistical tests were two-sided.

In June through July 1997, 87 healthy participants who were 18-24 years old (51 females; 36 males) were recruited in Lyon and Lausanne for the trial. One participant was considered lost to follow-up (French, female, skin type III, SPF 30 group) after she did not attend the second medical examination in September and did not return the daily record diary to study investigators. This subject could not be included in the analysis.

There was no major imbalance in the distribution of baseline characteristics between the two groups (Table 1 ), who showed similar patterns of skin phototype, skin complexion, past sun-exposure habits, sunburn experience, and sunscreen use. SPF 10 participants spent their holidays in 139 different areas, of which 47% were countrysides or lakes, 26% were very sunny areas (e.g., the Mediterranean coast), and 27% were other places (e.g., swimming pools in cities). SPF 30 participants spent their holidays in 127 different areas, of which 50% were countrysides or lakes, 28% were very sunny areas, and 22% were other places.

In both groups, the duration of holidays and the number of sunny days during which they either sunbathed or had outdoor activities were equivalent (Table 2 ). Participants used nearly equal quantities of sunscreen, and none exhausted the sunscreen received at the initial medical visit. The average quantity of sunscreen used represented 20% of the quantity received, ranging from 0% to 65% (one participant in the SPF 30 group did not use any sunscreen at all). Sunscreen use was associated more with sunbathing activities than with outdoor activities (data not shown).

The use of the SPF 30 sunscreen was associated with a greater number of hours spent in the sun (Table 2) . Sun exposure of participants who used the SPF 30 sunscreen was, on average, 25% longer than that of participants who used the SPF 10 sunscreen. The higher sun exposure associated with the SPF 30 sunscreen was observed in both study sites. To verify that the observed difference was not due to exceptional sun exposure of some SPF 30 participants, we analyzed the data after elimination of one participant in the SPF 10 group and two participants in the SPF 30 group having total sun-exposure duration three standard deviations above the mean. The difference in the number of hours spent in the sun remained about the same.

The mean daily duration of sun exposure, sunbathing, or outdoor activities was calculated by use of the number of days on which these activities occurred. The increase in daily sun exposure associated with the SPF 30 sunscreen was observed mainly for sunbathing activities. The increase in sunbathing duration was retrieved in the three subgroups of skin color at initial medical examination, despite the small numbers of participants in the skin color categories.

The starting hour of sunbathing activities was identical in both groups during the first holiday day with sunbathing (Fig. 2) . As the holidays progressed, however, SPF 30 participants tended to start sunbathing systematically earlier than SPF 10 participants, resulting in more sun exposure during the middle of the day.

The numbers of sunburns or of skin-reddening episodes were comparable in both groups (Table 2) . Despite the use of potent sunscreens, 45% of the participants reported one or more sunburns and 81% reported one or more skin-reddening episodes. There was no association between the quantities of sunscreen used and the number of sunburn or skin-reddening episodes (data not shown). Body sites involved in skin-reddening or sunburn episodes were similar in the two groups (data not shown), except for the anterior part of the trunk, where nine women in the SPF 10 group and three in the SPF 30 group reported at least one skin-reddening or sunburn episode ( P = .075).

Because clothes normally cover them during time spent outdoors, women's breasts are highly sensitive to the sun. Five women in the SPF 10 group and eight in the SPF 30 group sunbathed with naked breasts (Table 3 ). All sunbathing sessions with naked breasts were preceded by sunscreen applications to the trunk. While duration of holidays and numbers of skin erythemal episodes were identical in the two groups of women, the use of the SPF 30 sunscreen was associated with five times longer sunbathing with naked breasts. Also, while women in the SPF 30 group were more inclined to sunbathe with naked breasts in the early days of their vacation, most women in the SPF 10 sunscreen group waited at least 1 week before exposing their breasts to the sun.

To verify that our results were not the consequence of multiple small confounding effects, we fitted a least-squares regression model using accumulated hours of sun exposure as the dependent variable. The model included number of days of holidays, number of sunscreen applications, randomization group, number of sunburns, sex, and study site. The main predictors of accumulated sun exposure were the duration of holidays ( P <.001) and the number of daily sunscreen applications ( P = .008). These results are not surprising, since duration of sun exposure is positively associated with duration of holidays and staying in the sun encourages sunscreen use. The SPF of the sunscreen used was a statistically significant predictor of duration of total sun exposure ( P = .010), independent of the effect of other variables. The remaining variables were not associated with sun-exposure duration ( P >.20 for all).

Eleven French participants, seven in the SPF 10 group and four in the SPF 30 group, used another sunscreen than that provided. Alternative products were used, for a total of 18 days in the SPF 10 group and 7 days in the SPF 30 group. The SPFs of the alternative sunscreens were 5, 6, 6, 10, 10, 20, and 20 in the SPF 10 group and 8, 30, 30, and 60 in the SPF 30 group (Wilcoxon rank sum test for the difference in SPF: P = .070), suggesting that alternative products used by SPF 30 participants were of higher SPF than alternative products used by SPF 10 participants.

The results of this randomized trial demonstrate that recreational sun exposure is of longer duration when a high SPF sunscreen is used than when a low SPF sunscreen is used. Similar results were found in two independent study sites and mainly concerned sunbathing activities. Two findings in particular attest to the sense of security conferred by potent sunscreens. First, the use of the SPF 30 sunscreen led to a greater amount of sunbathing during hours of the day during which the UV radiation usually reaches its peak value. Second, women using the SPF 30 sunscreen sunbathed longer with naked breasts while incurring a lower number of sunburns or skin-reddening episodes on that part of the body.

Participants in the two study arms were similar in terms of natural susceptibility to sunlight, history of sun exposure and sunburn, duration of holidays, and the types of places they vacationed. Furthermore, our data suggest that those participants who used SPF 30 sunscreen actually increased their sun exposure over the course of the holidays (Fig. 2) . Therefore, it is unlikely that the difference in sun-exposure duration stemmed from differences in baseline characteristics and choice of holiday location; rather, it appears to be related to protection from burning conferred by the stronger sunscreen.

Data collection was done prospectively by use of standard diaries completed on a daily basis. Therefore, biases in the recording of sun-exposure duration have probably been minimal. If some bias was present, however, it is reasonable to assume that it has been equally distributed among the two study groups. We thus consider that the reported sun-exposure durations in this study are a valid reflection of the true sun exposure of participants during their holidays and that our findings are unlikely to be due to bias.

An adult should use roughly 35 mL of sunscreen per single whole-body application to correspond to the doses used by laboratories for measuring the SPF of a sunscreen ( 20 ). In that respect, our study participants should have consumed at least three to four times the quantities actually used, and it is thus probable that, in most participants, the effective SPF of the sunscreens used was about three to four times lower. However, our study shows that an increased ability to delay sun-induced skin erythemal reactions is sufficient to cause longer sun exposure, even when moderate quantities of sunscreen are used.

The increase we observed in sun-exposure duration may explain why sunscreen use has been reported to be a risk factor for melanoma, basal cell cancer, and nevus development. It also demonstrates that the longer sun exposure allowed by sunscreen use is an unconscious phenomenon, which makes individual control difficult, particularly where children are concerned.

Sunburn or skin-reddening experience among participants was independent of the SPF and of the quantity of sunscreen used. This observation suggests that sunscreen use during recreational sun exposure does not imply protection against sunburns. Sunburns are essentially due to the UV B radiation ( 1 ). Equivalence of sunburns and skin-reddening experiences in the two groups suggest that doses of UV B radiation received by skin cells were probably similar in the two groups. However, the delivery of these doses to skin cells of SPF 30 participants would have taken a longer time than that to skin cells of SPF 10 participants.

The issue addressed by this study is common to all sunscreens. Because we did not want to single out the products of a specific company, we chose not to disclose the commercial name and the exact composition of the sunscreens used in this trial.

From our results, it is reasonable to infer that equivalent or greater differences in sun-exposure duration would have been observed if one had compared subjects using a sunscreen with subjects not using any sunscreen. One could have considered a placebo-controlled trial using as placebo a lotion without any chemical or physical substance able to block UV radiation. In this study, a placebo group was not possible. First, it was ethically difficult to allow a placebo sunscreen when the sun-protection virtues of sunscreens are widely acknowledged. Second, it was not easy to provide a placebo sunscreen without informing subjects of both study groups that they should be careful in their sun exposure to avoid severe sunburns. Third, many subjects in the placebo group would have rapidly changed to a real sunscreen, which would have endangered the trial.

Experiments that tested the ability of sunscreens to reduce the incidence of UV-induced lesions have not examined the possibility that these products could modify the sun-exposure behaviors of subjects eager to acquire a tan or to stay in the midday sun with large parts of the body uncovered. The two human placebo-controlled trials that showed the ability of sunscreen use to reduce the incidence of actinic keratoses ( 6 , 7 ) enrolled subjects having a mean age of 64 years who had a history of nonmelanoma skin cancer or of other sun-induced skin lesions, who were highly aware of the hazards of sun exposure, who were not keen to acquire a suntan, and who apparently never had sunburn during the trials. Clearly, these trials did not reproduce the normal or reasonably foreseeable conditions of sunscreen use in North America and Europe, where sunscreen use by younger people remains largely driven by the desire to enjoy the sun and to acquire a “safe suntan” ( 21 - 24 ).

The protective effect of sunscreen use against skin cancer, particularly melanoma, has not been demonstrated in the general population, but there are compelling data that show a strong relationship between duration of recreational sun exposure and skin cancer. It is therefore desirable that people should be warned against the danger that using a sunscreen may inadvertently prolong recreational sun exposure.

Baseline characteristics of participants

SPF = sun-protection factor.

When going in the sun, a skin phototype I subject always burns and never tans, a skin phototype II subject always burns first and tans after, and a skin phototype III subject sometimes burns but always gets a deep tan ( 19 ). In this study, there were no skin phototype IV subjects (i.e., who never burn and always get a deep tan).

Determined by examining the inner side of upper arms.

Sun exposure and sunburn experience during holidays *

SPF = sun-protection factor; 95% CI = 95% confidence interval.

Student's t test for testing of difference between means, χ 2 statistics for testing of difference between numbers; P values are two-sided.

Because of bad weather, or of absence of eagerness to go outside, or of a sunburn in the previous days.

One participant in SPF 30 group did not use any sunscreen.

Exclusion of participants with total sun exposure three standard deviations above the mean: one participant in the SPF 10 group (126 hours of total sun exposure) and two participants in the SPF 30 group (127 and 199 hours of total sun exposure).

Accumulated hours of sun exposure, outdoor activities, or sunbathing divided by the number of days during which there was sun exposure, outdoor activities, or sunbathing.

Sunbathing with naked breasts in female participants

For definition, see footnote in Table 1 .

Wilcoxon rank sum test for the difference in median hours of sunbathing with naked breasts; two-sided P = .030.

Trial design.

Mean hour of start of sunbathing activities in days with sunbathing. Days without sunbathing were skipped. The time in the figure is the so-called “summer hour” in Continental Europe, equivalent to the solar hour plus 2 hours. Blank squares represent sun-protection factor (SPF) 30 participants; black circles represent SPF 10 participants. Error bars represent 95% confidence intervals. Student's t test for the difference in mean hour: P >.90 for the first day; P <.050 for days 2-9 ( P values are two-sided).

Supported by grants from the Lions Club of Bourg en Bresse (France) and from the Europe Against Cancer Programme of the European Commission. Neither the European Commission nor any person acting on its behalf is liable for any use made of the contents of this article.

We thank Professor T. Philip, Centre Léon Bérard (Lyon, France), for his supportive interest in this work; M.-J. Blasco, Auchan Hypermarkets (Lyon), and H. K. Marchand for their help in the provision and repackaging of sunscreens; and M. Friedrich (Lyon), Dr. K. Buxtorf, and Dr. M. Derighetti (Lausanne, Switzerland) for their assistance.

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• sunscreening agents
• sun exposure

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Science Fun

Sunscreen And Skin Human Body Science Experiment

In this fun and easy human body science experiment for kids, we’re going to explore skin and sunscreen. 

• Sunscreen lotion
• Black or dark colored construction paper

Instructions:

• Fold the construction paper in half to create two sections.
• Put a small dab of sunscreen on one side of the paper. Rub it in to the construction paper ensuring to keep the sunscreen on just one side of the paper.
• Put the paper in direct sunlight for most of the day.
• Observe any changes to the paper.

EXPLORE AWESOME SCIENCE EXPERIMENT VIDEOS!

How it Works:

In this experiment, the construction paper acted as our skin. The area not protected by sunscreen should have faded throughout the day demonstrating the sunscreen’s ability to protect human skin. 

Make This A Science Project:

Try different brands of sunscreen. Try different SPFs of sunscreen. 

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