The number on a bottle of sunscreen is measured on a film 2 milligrams thick on every square centimeter of skin. For an adult body that is about 36 grams of lotion, close to a full shot glass. In 1992 two dermatologists from Copenhagen, Niels Bech-Thomsen and Hans Christian Wulf, measured how much 42 people on a beach put on when they used their own sunscreen all over. The average was 0.5 milligrams, a quarter of the test amount. 1
Other groups have measured it since, and the answer stays low. A team working with the European Organisation for Research and Treatment of Cancer gave SPF 10 or SPF 30 sunscreen to 124 students aged 18 to 24 before their summer holidays in 1997 and 1998 and recorded how much each one used and where they put it. The median student had spread 0.39 milligrams per square centimeter. It made no difference whether they were men or women, what their skin type was, or which product they had. 2
A sunscreen is a film of chemicals that absorbs or scatters ultraviolet light before it reaches the living cells of the skin. People have used sunscreens for more than a century. Researchers tested them first against sunburn, then against skin cancer, and since 2019 for what they do after they soak in.
The one randomized trial of daily sunscreen and skin cancer, in the Queensland town of Nambour, found about 40 percent fewer squamous cell carcinoma tumours in the daily group, no change in basal cell carcinoma, less visible skin aging, and half as many melanomas, a count too small to be sure of.
Two trials run by the US Food and Drug Administration found that the common sunscreen chemicals reach the blood within a day, at levels above the agency's threshold for further safety testing. The trials measured absorption, not harm, and no study has shown that those levels harm anyone. In a 2013 survey of 4,033 American adults, 14 percent of men and 30 percent of women said they regularly used sunscreen on both the face and other exposed skin. 3; 4; 5; 6; 7; 8
This page covers where sunscreen came from, what the SPF number measures, what daily use prevented in the trials, how people behave once they have it on, what the filters do inside the body, and how regulators, reefs, and a contaminant entered the argument. Each study is named as real sun, a lamp, sunscreen applied to people, animal feeding, cells, or a measurement in blood, urine, or milk.
Key facts
- In the Nambour trial, daily sunscreen on the head, neck, arms, and hands for 4.5 years cut squamous cell carcinoma tumours to 1,115 per 100,000 against 1,832, and left basal cell carcinoma unchanged. 3
- In the 2020 FDA trial, one application of sunscreen took all six common sunscreen chemicals above 0.5 nanograms per milliliter of blood, and 22 of 23 people who used oxybenzone were still above it 17 days after their last dose. 7
- People on beaches and holidays apply about 0.4 to 0.5 milligrams per square centimeter, a quarter or less of the 2 milligrams used to measure the SPF. 1; 2
- Students given SPF 30 in place of SPF 10 spent 72.6 hours in the sun over their holidays against 58.2, and burned no less. 9
- Photoallergy to sunscreen chemicals was found in 4.4 percent of 1,155 patients tested for light-triggered rashes in the UK and Ireland, most often to oxybenzone. 10
The first sunscreens were sold to tan without burning
The first recorded sunscreen was quinine. In 1891 a German doctor named Hammer made it into a lotion or ointment for his patients. Other remedies followed at intervals of a decade or so: plant extracts, tannic acid, and by 1931 benzyl salicylate, the ingredient in the first commercial products. In 1935 Eugène Schueller, the founder of L'Oréal, brought out a sun oil called Ambre Solaire. The next summer French workers took their first paid holidays, and the product sold for the beach. 11; 12
In December 1942 Colonel Otis Benson of the Army Air Forces asked the American Medical Association which substance best protected airmen from sunburn, and the physicist Matthew Luckiesh's laboratory at General Electric tested the candidates. The answer was red veterinary petrolatum, a thick red grease left over from refining oil. It was "standard equipment in life rafts and vehicles engaged in tropical warfare", in the words of two dermatologists who wrote its history in 1964. The popular story that the Miami Beach pharmacist Benjamin Green invented it has no support in the record. Green did launch Coppertone in 1944, as a suntan product. 13; 14
Also in December 1942, Stephen Rothman and J. Rubin in Chicago reported that para-aminobenzoic acid, better known as PABA, prevented sunburn. PABA absorbs the short, burning part of ultraviolet, called UVB, and lets most of the longer UVA through, and UVA was then taken for the tanning ray. A 2009 history of the American rules gives the aim of the old suntan preparations in their own terms: to "screen out the burning rays of the sun" and "admit the tanning rays". 15; 16
"The purpose of a sun tan or sun-filtering preparation is to produce a tanning of the skin with a minimum of erythema," a doctor in New Jersey wrote in 1950, erythema being the medical word for redness. He was describing the first reported skin reaction to PABA, in a 25-year-old student who had spent a weekend at the beach. 17
Some of the largest early tests of sunscreen were run on prisoners. From 1965 to 1968 Madhu Pathak, Thomas Fitzpatrick, and Edgar Frenk of Harvard, paid by the US Army Research Office, tested products on 156 volunteers at the Arizona State Prison in Florence and 19 more on a glacier in the Swiss Alps, 2,900 meters up. The volunteers lay in the sun, did calisthenics until they sweated, and swam. None of the 24 commercial products on sale protected for more than an hour. A solution of 5 percent PABA in alcohol protected all day for anyone who stayed dry.
In Philadelphia, Albert Kligman's group tested PABA on "white, male prisoner volunteers" under a xenon lamp and titled one 1972 paper "Tanning Without Sunburn With Aminobenzoic Acid-Type Sunscreen". 18; 19
PABA declined in the 1980s. It stained clothes yellow and it caused allergies, sometimes in the people who most needed it. In 1978 a Kyoto group reported a 6-year-old girl with xeroderma pigmentosum, an inherited disease in which the skin cannot repair ultraviolet damage, who had become allergic to the PABA she wore against the sun.
In 1979 Robert Sayre and his colleagues at Schering-Plough, the maker of Coppertone, reported that a mix of a PABA ester called padimate O with 3 percent oxybenzone beat every other formula they tested, including plain PABA. The winner was their own company's product. Oxybenzone, a benzophenone, absorbs into the UVA as well as the UVB, and it spread through the market over the following decades. The FDA removed PABA from its list of permitted sunscreen ingredients on 11 September 2026. 20; 21; 16; 22
The SPF measures sunburn from a lamp under a film thicker than people use
The sun protection factor is a ratio. A technician shines a lamp on small patches of a volunteer's back, some bare and some under 2 milligrams per square centimeter of the product, and finds the smallest dose that leaves each patch just visibly red the next day. That dose is called the minimal erythema dose. The SPF is the dose that reddens protected skin divided by the dose that reddens bare skin. An SPF of 30 means the lamp had to deliver 30 times as much ultraviolet to cause the same faint redness. The FDA's rule since 2011 asks for ten volunteers. 23
The method began outdoors. Rudolf Schulze, a German researcher, published a way to measure protection on people in 1956 and measured it in the natural sunlight of the Alps. Franz Greiter, an Austrian chemist who founded the Piz Buin brand and is said to have started after a sunburn on that mountain, gave the number its name, sun protection factor, in a 1974 paper. Two researchers who reviewed the history in 2022 wrote that lamp-measured SPF values run higher than protection measured in real sunlight. 24
The film people really wear is much thinner, and protection falls with it. In 2018 Antony Young's group at King's College London spread a sunscreen whose tested SPF was 64 on the upper buttocks of fair-skinned volunteers at three thicknesses. At 0.75 milligrams per square centimeter, near what people use, it measured SPF 20.9. The researchers then gave the skin a lamp dose and counted the DNA damage. At that thinner layer the reduction in damage was mostly too small to be distinguished from none. Each volunteer had a personal tube of sunscreen that was weighed before and after. 25
Some products do not reach their label even at the full thickness. Consumer Reports tested 65 water-resistant American sunscreens labeled SPF 30 or higher in 2016 and found 28 below the label, two children's products at SPF 8.
In June 2025 the Australian consumer group CHOICE had 20 sunscreens labeled SPF 50 or 50+ tested and found 16 below their claims. One, Ultra Violette's Lean Screen, tested at SPF 4, and a second laboratory in Germany gave it 5. The Therapeutic Goods Administration, which regulates sunscreen in Australia as a medicine, then found that a shared base formula from one manufacturer, Wild Child Laboratories, was unlikely to exceed SPF 21. The agency said it had "significant concerns about the reliability" of a British laboratory, Princeton Consumer Research, whose results many brands had relied on. Consumer groups test each product once, on a few people, and several brands disputed the method. 26; 27; 28
SPF is almost entirely a measure of UVB, because UVB does most of the reddening. UVA makes up most of the ultraviolet that reaches the ground, reaches deeper into the skin, and burns only in large doses. In 2010 a London group gave eight fair volunteers small daily lamp doses for 13 days, some patches under a UVB-only SPF 6 sunscreen and some under an SPF 6 that also blocked UVA. "UVA makes a greater contribution toward sunburn at temperate latitudes than under the laboratory conditions in which SPF is tested and assigned," they wrote. 29
UVA also weakens the skin's immune reactions. In 2003 a Cleveland group working with L'Oréal gave 211 volunteers a dose from a solar simulator, a lamp built to imitate sunlight, on the buttock, with or without sunscreen, and two days later sensitized them to a test chemical, dinitrochlorobenzene. Two weeks on they measured how strongly the arm swelled when the chemical was applied again. Of two sunscreens that were both SPF 15, the one with strong UVA protection protected that reaction by a factor of 50 and the one with weak UVA protection by a factor of 15. 30
The FDA's 2011 labeling rule turned broad spectrum into a pass or fail test. A thin film of the product on a roughened plate has to absorb light across the spectrum up to a critical wavelength of 370 nanometers, well into the UVA. The same rule set "water resistant" at 40 minutes of swimming and "very water resistant" at 80, and it barred the words "sunblock", "waterproof", and "sweatproof" as "exaggerations of performance". Products without broad spectrum, or below SPF 15, must carry a warning that they have been shown only to help prevent sunburn, "not skin cancer or early skin aging". 23
Daily sunscreen reduced keratoses, squamous cell carcinoma, and skin aging in Australian trials
The first trial that asked whether sunscreen prevents anything but sunburn ran in Victoria for one summer, from September 1991 to March 1992. Thompson, Jolley, and Marks gave 588 people aged 40 or older either an SPF 17 broad-spectrum cream or the same cream without its filters, to put on the head, neck, forearms, and hands. They counted solar keratoses, the rough scaly patches of sun-damaged skin that sometimes turn into squamous cell carcinoma. Over the summer the base-cream group gained an average of one keratosis each and the sunscreen group lost 0.6. The more cream a person used, the better the result. 31
The Nambour trial ran longer. In 1992 Adele Green's group in Brisbane enrolled 1,621 residents of Nambour, a Queensland town at latitude 26 degrees south, and assigned them by chance to one of four groups: a daily SPF 15-plus sunscreen with beta-carotene tablets, the sunscreen with dummy tablets, beta-carotene alone, or dummy tablets alone. The daily group put the sunscreen on the head, neck, arms, and hands every morning. Staff weighed the bottles at every visit to check. The other half used sunscreen as they pleased, so the trial compared daily use with habit, not with none. 3; 32
After four and a half years a dermatologist had examined 1,383 of them, and 250 people had developed 758 new skin cancers. Counted as tumours, squamous cell carcinomas ran at 1,115 per 100,000 in the daily group against 1,832, about 40 percent fewer. Counted as people with at least one new squamous cell carcinoma, the difference was small and uncertain, 876 against 996. Basal cell carcinoma, the commonest skin cancer, did not change at all: 2,588 against 2,509 people per 100,000. Beta-carotene did nothing for either. 3
The same trial measured aging. Researchers made silicone casts of the skin surface of the 903 participants under 55 in 1992 and again in 1996, and assessors who did not know who had been in which group graded the fine lines. The daily sunscreen group showed no detectable increase in skin aging over the four and a half years, and its aging was 24 percent less than the other group's. The authors noted that some outcome data were missing and that the trial could detect only fairly large effects. 4
Nambour's follow-up to 2006 found 11 new melanomas in the daily group against 22. Melanoma was not what the trial had been built to measure, and the counts are small. Allowing for chance, the true effect could lie anywhere from about three quarters fewer melanomas to slightly more. The trial and the observational studies around it are on the melanoma page. 5
Under a lamp, sunscreen stops DNA damage almost completely. In a 2002 study 18 women took two minimal erythema doses from a solar simulator on each of four days. Skin under a daily SPF 15 had 7 cells per square millimeter carrying a kind of ultraviolet DNA damage called the thymine dimer, the same as skin that had never been irradiated. Skin whose sunscreen was skipped that day had 495. 33
When a 2018 meta-analysis, a study that pools the results of earlier studies, combined five observational studies with 857 cases, people who used sunscreen had the same odds of basal or squamous cell carcinoma as those who did not. The people who reach for sunscreen are also the people who burn easily, and questionnaires cannot pull the two apart. 34
People given stronger sunscreen spent longer in the sun
In 1997 Philippe Autier's group randomly gave 87 French and Swiss students aged 18 to 24 either an SPF 10 or an SPF 30 sunscreen before their summer holidays. Neither the students nor the doctors knew which was which. To keep the students from changing their habits, the researchers gave no advice and told them the study was about moles.
The two groups took holidays of about the same length and used about the same amount of sunscreen, near 72 grams each. The SPF 30 group spent 72.6 hours in the sun against 58.2, sunbathing about half an hour longer every day. Both groups burned equally often. 9
The trial was small and relied on the students' own diaries. The trial suggests one reason that observational studies kept finding more skin damage in sunscreen users. A stronger product may lead to a longer afternoon in the sun, and the same burn at the end of it. When 25 people from Denmark went to the Canary Islands for a week wearing ultraviolet meters, every one of them burned at some point, though most used sunscreen. The story of that holiday is told on the sunburn page. 35
Stronger products do prevent more redness when the time outdoors is held equal. In 2018 Johnson and Johnson, which makes both products and paid for the study, had 199 adults in Vail, Colorado, wear SPF 100+ on one half of the face and SPF 50+ on the other for a day of about six hours in the mountain sun. Neither the volunteers nor the assessors knew which side was which. Afterward 110 people were more sunburned on the SPF 50+ side and 10 on the SPF 100+ side. 36
Common sunscreen chemicals reach the blood within a day of use
For most of its history sunscreen was assumed to stay on the skin. A Copenhagen team tested that in 2004. Thirty-two volunteers, 15 young men and 17 women past menopause, spread 2 milligrams per square centimeter of cream over the whole body every day for two weeks, plain cream in the first week and in the second the same cream with 10 percent each of three sunscreen chemicals: oxybenzone, octinoxate, and 4-methylbenzylidene camphor. The women were chosen because their own estrogen is low, so an estrogen-like chemical would show.
Oxybenzone reached about 200 nanograms per milliliter in the women's blood and 300 in the men's. The hormones that control the testes and ovaries did not change. There were small differences in testosterone and in estradiol, the main estrogen, which the authors wrote "were not related to sunscreen exposure." 37
The FDA took up the question in 2018. Its scientists, led by Murali Matta, ran two trials at a clinical research unit in West Bend, Wisconsin. The volunteers stayed inside the clinic and never went into direct sunlight. A staff member weighed each dose in advance and spread it on at 2 milligrams per square centimeter over three quarters of the body, everything a swimsuit would leave bare.
In the first trial, in July and August 2018, 24 adults did this four times a day for four days, and gave 30 blood samples over a week. All four products, two sprays, a lotion, and a cream, took their filters above 0.5 nanograms per milliliter on the first day. Oxybenzone peaked at 170 to 210. 6
The second trial, in January and February 2019, gave 48 adults one application on the first day and then four a day for three days, and drew blood 34 times over three weeks. All six filters tested passed 0.5 nanograms per milliliter after the single first application: avobenzone, oxybenzone, octocrylene, homosalate, octisalate, and octinoxate. Oxybenzone reached 258 nanograms per milliliter from the lotion.
Three weeks later, 17 days after the last dose, 22 of the 23 oxybenzone users and 17 of 31 homosalate users were still above the threshold. Tape strips pulled from the lower back found the filters still in the outer skin at days 7 and 14. The authors took this to mean that the skin releases the filters slowly. Fourteen of the 48 developed a rash. 7
The 0.5 nanograms per milliliter is not a level at which anything is known to go wrong. It comes from a principle the FDA first applied to chemicals that migrate from food packaging into food: the concentration below which, for any untested compound, the cancer risk from a single dose would be under 1 in 100,000. Above it, the rules say, a drug ingredient needs the toxicology studies that the FDA had asked sunscreen makers for and not received. "These results do not indicate that individuals should refrain from the use of sunscreen," the authors of the first trial wrote. 6
Both trials used the amount at which the SPF is tested, on three quarters of the body, several times a day. They measured absorption only, indoors in a clinic, with no heat, sweat, or sun, on 6 to 12 people per product.
In 2019 a Brisbane group put nanoparticles of zinc oxide, the mineral filter in many sunscreens, on the skin of five volunteers every hour for six hours and every day for five days, then looked into the living skin with a laser microscope. The particles gathered on the surface and in the skin's furrows and did not enter the living layer. In 2010 a CSIRO team in Sydney put zinc oxide made with a rare, heavy form of zinc on 20 volunteers at a beach and found that zinc in their blood and urine, in amounts "small compared with the amounts of Zn normally present in the human body". A later test in three people put the share reaching the blood at under 0.01 percent. 38; 39; 40
In 2019 the FDA proposed that only zinc oxide and titanium dioxide could be called generally recognized as safe and effective. Twelve other filters, oxybenzone and avobenzone among them, needed more data. As of September 2026 the agency has not ruled on those twelve, and they remain on sale. 41; 22
Oxybenzone is in the urine of almost every American tested
Oxybenzone leaves the body in urine, and national surveys have been counting it there since 2003. Antonia Calafat's laboratory at the Centers for Disease Control and Prevention found it in 96.8 percent of the urine samples from the 2003 to 2004 National Health and Nutrition Examination Survey, a sample built to represent the whole American population. Oxybenzone is also added to other cosmetics and some plastics. Non-Hispanic white Americans were 6.8 times as likely as non-Hispanic Black Americans to be in the top 5 percent. 42
When National Cancer Institute researchers matched urine to what 4,412 survey participants said about their habits, oxybenzone rose in step with sunscreen use. People who said they never used sunscreen averaged 9.3 micrograms per gram of creatinine, the waste product used to correct for how dilute urine is. Those who used it always averaged 116.8. The people who said never still carried some. 43
In Basel, 54 mothers gave samples of their milk in late summer and autumn from 2004 to 2006, and 85 percent held at least one ultraviolet filter.
A Barcelona study found oxybenzone in 23 percent of 79 samples from a milk bank, then tested the bank's own plastic containers and found oxybenzone in them as well, up to 10.6 micrograms per gram of plastic.
Filters have been found in placentas and in blood from the umbilical cord. Studies disagree on how freely they cross: one Danish study measured oxybenzone in fetal blood at about a tenth of the mother's level, and one in Guangzhou found the two about equal. 44; 45; 46; 47; 48
In 2018 a British group measured four filters in breast tissue removed at surgery from 40 women in England, three samples each. At least one filter was in 101 of the 120 samples. None of these measurements was linked to any outcome in a mother, a baby, or a breast. 49
Oxybenzone acts like a weak estrogen in rats at doses far above human use
From about 2001 several laboratories fed or injected rats with ultraviolet filters and weighed their wombs, which grow under estrogen. Some filters, oxybenzone among them, made the wombs heavier. A Tsukuba team tested benzophenone-1, which the body makes from oxybenzone, in 2005 and put its potency at roughly one ten-millionth of that of the estrogen in birth control pills. "UV screens contain weak estrogenic compounds," they wrote. 50
In 2011 three dermatologists worked out how much sunscreen a woman would need to match the dose given to the rats in one of the best-known of those studies. At 2 milligrams per square centimeter of a 6 percent oxybenzone sunscreen over the whole body, every day, it would take 34.6 years. At the thinner layers people use, over a quarter of the body, it would take 277. 51
The US National Toxicology Program ran the largest animal study. It mixed oxybenzone into the feed of pregnant rats and followed their offspring. It chose feed over skin, the report explains, because rats groom each other, and a dose on the fur would end up in someone else's mouth. The program found "equivocal evidence" of harm to reproduction, "some evidence of developmental toxicity" in the form of lighter pups, and a scatter of hernias of the diaphragm in exposed litters that it could not firmly attribute to the chemical. The pregnant rats ate from about 200 to more than 2,600 milligrams of oxybenzone per kilogram of body weight a day. 52
The human studies are associations drawn from urine. In the American LIFE study of couples trying to conceive, men with more of the filter benzophenone-2 in their urine had lower sperm concentrations, and couples with more of it had more daughters. A 2020 review of 29 human studies found no effect on fertility, body fat, growth in the womb, or brain development, and some links with thyroid hormones, testosterone, kidney function, and the timing of puberty that it said called for more work. A single urine sample shows recent exposure, from sunscreen and everything else, and most of these studies could not say where the chemical came from. 53; 54; 55
The European Union acted on the concern in 2022. It capped oxybenzone at 6 percent in face, hand, and lip products and 2.2 percent in body products, and required the label "Contains Benzophenone-3". Its scientific committee first judged homosalate safe only up to 0.5 percent, a twentieth of the old limit, then after more data allowed 7.34 percent in face products alone. 56; 57
No study has tested whether absorbed sunscreen chemicals cause cancer in people
For skin cancer, the evidence in people points the other way. The one randomized trial found fewer squamous cell carcinomas and fewer melanomas in daily users. The early observational studies that found more melanoma among sunscreen users could not separate sunscreen from the people who buy it, who are often the people who burn. 3; 5; 34
The question about the filters themselves has not been tested. We found no study in people that followed sunscreen users for cancers of other organs. When the FDA asked in 2019 for more safety data on twelve filters, including two-year cancer studies in rodents, an industry consortium answered in 2025 with a review arguing that six of them lacked any mechanism to cause cancer and that the bioassays were unnecessary. The review was paid for by the Personal Care Products Council's sunscreen consortium, whose members include L'Oréal, Beiersdorf, Unilever, and Procter and Gamble. 41; 58
A different cancer concern arrived in 2021 and had nothing to do with the filters. Valisure, a testing laboratory in New Haven, analyzed 294 batches of sunscreen and after-sun products from 69 companies and found benzene, a chemical known to cause leukemia, in 78 of them. Fourteen batches from four brands held between 2.78 and 6.26 parts per million. Benzene is not a sunscreen ingredient FDA guidance says benzene "should not be employed" in making drugs and tolerates up to 2 parts per million only where its use is unavoidable.
Johnson and Johnson recalled every lot of five Neutrogena and Aveeno aerosol sprays in July 2021, saying the levels found "would not be expected to cause adverse health consequences." We found no final FDA answer to Valisure's petition. 59; 60
Allergy to sunscreen chemicals is rare in general and common among people tested for light rashes
In contact allergy the skin reacts to a sunscreen chemical itself. In photoallergy it reacts only when the chemical is on the skin and light falls on it. Dermatologists test for both by taping small amounts of each chemical to the back, then shining a UVA lamp on one set of patches and not the other.
How common the allergy looks depends on who is tested. Of 23,908 patients patch tested for rashes by the North American Contact Dermatitis Group from 2001 to 2010, 219, or 0.9 percent, had a sunscreen as the source of an allergy, oxybenzone in about 70 percent of those. In 64 unpublished industry studies of sunscreens with oxybenzone, reviewed by Schering-Plough staff in 2008, 8 confirmed allergies turned up in 19,570 possible reactions.
Among people already referred for rashes that appear in sunlight the rate is higher. A study at 17 centers in the UK, Ireland, and the Netherlands tested 1,155 of them and found photoallergy in 51, or 4.4 percent, and oxybenzone was the commonest cause. Most of those 51 had not known a sunscreen was the problem. 61; 62; 10
In 2010 a French group gathered 50 cases of allergy to octocrylene, a newer filter. The 11 children had ordinary contact allergy. Of the 28 adults sensitized by sunscreen, 24 had earlier reacted to ketoprofen, a painkilling gel sold in Europe, and whose molecule contains a benzophenone. In 2021 a group in Antwerp and Leuven tested 28 sunscreens containing octocrylene and found benzophenone itself, as an impurity, in every one. The amount grew as the bottles were stored, and faster in heat. 63; 64
Sunscreen blocked vitamin D under a lamp and barely changed it on holiday
The skin makes vitamin D from UVB, the same light that burns it, so a sunscreen that stops the burn might be expected to stop the vitamin. In 1987 Michael Holick's group gave eight volunteers one minimal erythema dose from a lamp, four of them through an SPF 8 PABA sunscreen. Vitamin D in the blood of the unprotected four rose from 1.5 to 25.6 nanograms per milliliter, and in the protected four it barely rose. In 1988 the same researchers found that 20 people in Illinois who had used PABA sunscreen for years, most of them skin cancer patients, had less than half the vitamin D of 20 matched people from the same area. People who have had skin cancer may also avoid the sun, and the study could not separate the two. 65; 66
The trials in real sun found much less. In 1995 the Victoria group reported a trial of 113 people aged 40 or older who used an SPF 17 cream or a base cream through the summer. Their vitamin D rose by the same amount in both groups.
In 2019 Antony Young's group sent Polish volunteers from Łódź for a week in Tenerife in March, under a UV index of 9, and measured how much sunscreen they used: 2.4 milligrams per square centimeter, more than the test amount. Their vitamin D rose by 13 to 19 nanomoles per liter, against 28 in holidaymakers who used sunscreen as they pleased and a small fall in a group that stayed in Poland. The sunscreen groups did not burn. The discretionary group did. 67; 68
Oxybenzone harms coral larvae in the laboratory; its levels on Hawaii reefs were far lower
In 2018 Hawaii became the first state to ban the sale of sunscreens containing oxybenzone and octinoxate, from 1 January 2021. The law's findings state that the two chemicals "cause mortality in developing coral" and bleaching "even at temperatures below 87.8 degrees Fahrenheit". Palau banned ten ingredients from 2020. Key West voted a ban in 2019, and Florida's legislature voided it the next year by taking such rules away from cities. 69; 70
The main laboratory evidence came from a 2016 study led by Craig Downs of the Haereticus Environmental Laboratory in Virginia. The team exposed larvae of the coral Stylophora pistillata to oxybenzone. In light, half died within 24 hours at 139 micrograms per liter, and some larvae grew a skeleton around their own bodies. The team also reported oxybenzone in Hawaii's coastal water at 0.8 to 19.2 micrograms per liter. 71
When Carys Mitchelmore's group sampled 19 sites around Oahu in 2019, oxybenzone was below 10 nanograms per liter at 12 of them, a hundred to a thousand times lower than the earlier survey's Hawaii figures. The highest was Waikiki, up to 136 nanograms per liter. In 2022 a committee of the US National Academies reviewed 17 filters and found that several were toxic to some aquatic life in the laboratory, that "data are limited" for marine species, and that the field was not ready to judge the risk to reefs. It asked the Environmental Protection Agency to do that assessment for every marketed filter. It also noted that "reduced availability of consumer-preferred sunscreen formulations may lead to reduced use of sunscreens." 72; 73
The United States allows about half as many filters as Europe
The FDA regulates sunscreen as a drug sold without a prescription. Its advisory panel recommended 21 ingredients in 1978, and the list settled at 16 in a 1999 rule that the agency then put on hold. For the next 27 years no new filter entered that list. Filters used for years in Europe, bisoctrizole and drometrizole trisiloxane among them, stayed out of American products, and the FDA turned down applications for several of them for lack of data. L'Oréal won approval for one filter, ecamsule, through a full drug application in 2006, for its own products only. 41; 74
In June 2026 the FDA added bemotrizinol, a broad-spectrum filter long used in Europe, at up to 6 percent, on an application from the chemical company DSM. It was the first addition since the late 1990s and the first under a faster process that Congress created in 2020. In September 2026 the agency removed PABA and trolamine salicylate, which it had found in 2019 carried more risk than benefit. 75; 22
The European Union treats sunscreen as a cosmetic, and its list of permitted ultraviolet filters has 34 entries, about 30 of them in force. Australia treats sunscreen as a therapeutic good, which is why its medicines regulator investigated the 2025 SPF failures. 56; 28
Misconceptions
What people believe
- Sunscreen is mostly about avoiding a sunburn.
- SPF 30 means you can stay out 30 times as long.
- Sunscreen stays on the surface of the skin.
- The chemicals in sunscreen have been shown to cause cancer or hormone problems in people.
- Wearing sunscreen causes vitamin D deficiency.
- Sunscreen chemicals are what is killing coral reefs.
What the studies show
- In the Nambour trial daily sunscreen cut squamous cell carcinoma tumours by about 40 percent and slowed visible skin aging. It did not change basal cell carcinoma. 3; 4
- The SPF is measured under a lamp at 2 milligrams per square centimeter, and people use a quarter of that. A tested SPF 64 measured 20.9 at 0.75 milligrams. 25; 2
- The common sunscreen chemicals reached the blood within a day in both FDA trials, and oxybenzone stayed there for weeks. 7
- No study in people has shown that absorbed filters cause cancer or hormone disease. By one calculation, a woman would need 34.6 years of daily whole-body sunscreen to take in the oxybenzone dose of a well-known rat study. 51; 52
- In an Australian summer trial and a Tenerife holiday study, sunscreen use did not stop vitamin D from rising. 67; 68
- Oxybenzone harms coral larvae in the laboratory at concentrations far above those later measured on Oahu reefs. The effect on reefs is unmeasured. 71; 72; 73
Questions people ask
Does sunscreen cause cancer?
No study in people has found that sunscreen causes cancer. In the one randomized trial, daily users had fewer squamous cell carcinomas and fewer melanomas. The sunscreen chemicals are absorbed into the blood, and the long-term animal cancer studies the FDA asked for in 2019 have not been done for most of them. Some batches of aerosol sunscreen were contaminated with benzene in 2021. 3; 5; 7; 59
Does sunscreen prevent skin cancer?
Daily use prevented squamous cell carcinoma tumours and solar keratoses in Australian trials, and the melanoma result pointed the same way on small numbers. It did not prevent basal cell carcinoma over four and a half years. 3; 31; 5
How much sunscreen should I use?
The SPF on the label is measured at 2 milligrams per square centimeter, about 36 grams or a shot glass for an adult body. At a third of that, a product tested at SPF 64 gave SPF 20.9. 25
Is SPF 100 better than SPF 50?
In a one-day trial in Vail, Colorado, paid for by the maker of both products, more people burned on the SPF 50+ side of the face than on the SPF 100+ side, 110 against 10. Students given a stronger sunscreen also stayed out longer. 36; 9
Is mineral sunscreen safer?
Zinc oxide and titanium dioxide are the only two filters the FDA proposed as safe and effective in 2019. In volunteers, zinc oxide particles stayed on the skin surface and very little zinc reached the blood. 41; 38; 40
Does sunscreen block vitamin D?
Under a lamp, a PABA sunscreen blocked it almost completely. In real sun, over an Australian summer and a week in Tenerife, sunscreen users' vitamin D still rose. 65; 67; 68
Is sunscreen safe during pregnancy and breastfeeding?
Filters have been found in milk, placentas, and cord blood. No study has linked those levels to harm in a baby, and none has tested it directly. 44; 46; 47
What we do not know
Nobody knows whether the sunscreen chemicals that reach the blood do anything there. The FDA trials measured how much arrived, not what it did, and the studies of hormones in people rest on single urine samples from people exposed to the same chemicals in many other products.
The trials of sunscreen and skin cancer were run in one country, on mostly fair skin, under strong sun. Nambour is the only randomized evidence for squamous cell carcinoma and melanoma, and its melanoma result rests on 33 cases. None of the skin cancer trials enrolled mainly people with darker skin, and none tested children.
Why daily sunscreen reduced squamous cell carcinoma but not basal cell carcinoma is unexplained.
What sunscreen does to reefs is unknown. The laboratory work used larvae of a few species at high doses, and field measurements differ a thousandfold between surveys.
Key studies
- Bech-Thomsen and Wulf, 1992, Copenhagen. 42 people on a beach applied an average of 0.5 milligrams of sunscreen per square centimeter. 1
- Autier and colleagues, 2001, Europe. 124 students on holiday applied a median of 0.39 milligrams per square centimeter. 2
- Pathak, Fitzpatrick, and Frenk, 1969, Arizona and the Swiss Alps. No commercial sunscreen of 24 protected in real sun for more than an hour; 5 percent PABA in alcohol did. 18
- Sayre and colleagues, 1979, Memphis. A padimate O and oxybenzone mix beat PABA under a lamp and outdoors. 21
- Thompson, Jolley, and Marks, 1993, Victoria. One summer of SPF 17 reduced solar keratoses in 588 adults. 31
- Green and colleagues, 1999, Nambour. Daily sunscreen for 4.5 years cut squamous cell carcinoma tumours by about 40 percent and did not change basal cell carcinoma. 3
- Hughes and colleagues, 2013, Nambour. Daily users showed no detectable increase in skin aging over 4.5 years. 4
- Green and colleagues, 2011, Nambour. 11 new melanomas in the daily group against 22. 5
- Autier and colleagues, 1999, France and Switzerland. Students given SPF 30 spent 72.6 hours in the sun against 58.2 with SPF 10. 9
- Young and colleagues, 2018, London. A sunscreen tested at SPF 64 gave SPF 20.9 at the thickness people use. 25
- Williams and colleagues, 2018, Vail. SPF 100+ prevented more redness than SPF 50+ on the same faces in one day of mountain sun. 36
- Janjua and colleagues, 2004, Copenhagen. Whole-body application put oxybenzone into the blood of 32 volunteers without changing the hormones that control the testes and ovaries. 37
- Matta and colleagues, 2019, West Bend. Four sunscreens took their filters above the FDA's 0.5 nanogram threshold on the first day. 6
- Matta and colleagues, 2020, West Bend. All six filters passed the threshold after one application; oxybenzone persisted for three weeks. 7
- Calafat and colleagues, 2008, Atlanta. Oxybenzone in 96.8 percent of American urine samples. 42
- Bryden and colleagues, 2006, UK, Ireland, and the Netherlands. Photoallergy in 4.4 percent of 1,155 patients tested, oxybenzone first. 10
- Marks and colleagues, 1995, Victoria. Vitamin D rose equally with SPF 17 and base cream over a summer. 67
- Young and colleagues, 2019, Tenerife. Sunscreen at 2.4 milligrams prevented sunburn and allowed vitamin D to rise. 68
- Downs and colleagues, 2016, Hawaii and the Virgin Islands. Oxybenzone killed and deformed coral larvae in the laboratory. 71
- Mitchelmore and colleagues, 2019, Oahu. Oxybenzone below 10 nanograms per liter at 12 of 19 sites. 72
- National Toxicology Program, 2022. Equivocal reproductive effects and lighter pups in rats fed oxybenzone. 52
Definitions
- Avobenzone. A sunscreen chemical that absorbs UVA. It breaks down in light unless the formula stabilizes it.
- Benzophenone. A family of chemicals that includes oxybenzone (benzophenone-3). Benzophenone itself is found as an impurity in products made with octocrylene.
- Biomonitoring. Measuring a chemical in blood, urine, milk, or tissue to see how much of it reaches people.
- Broad spectrum. A US label that means a sunscreen's absorption reaches a critical wavelength of at least 370 nanometers, into the UVA.
- Contact allergy. An allergic skin reaction to a chemical touching the skin, with or without light.
- Generally recognized as safe and effective. The FDA's standard for an ingredient that can be sold without a prescription under its rules for that class of product.
- Mineral filter. Zinc oxide or titanium dioxide, filters made of fine particles of a metal oxide. The FDA proposed in 2019 that these two alone were safe and effective.
- Meta-analysis. A study that pools the results of earlier studies into one estimate.
- Minimal erythema dose. The smallest dose of ultraviolet that leaves a patch of a person's skin just visibly red a day later.
- Oxybenzone. A sunscreen chemical, also called benzophenone-3, that absorbs UVB and some UVA. It is the filter most studied for absorption, allergy, and hormones.
- Photoallergy. An allergic reaction to a chemical that happens only when light falls on the skin where the chemical is.
- Randomized trial. A study that assigns people to groups by chance, so that the groups differ only in what the researchers gave them.
- SPF. Sun protection factor. The ratio of the ultraviolet dose that reddens skin under 2 milligrams per square centimeter of a sunscreen to the dose that reddens bare skin, measured under a lamp.
- Solar simulator. A lamp built to give off a spectrum close to that of sunlight.
- Solar keratosis. A rough, scaly patch of sun-damaged skin, also called actinic keratosis. A small share become squamous cell carcinomas.
- Squamous cell carcinoma. A skin cancer of the flat cells near the surface of the skin, most common on skin that sees the most sun.
- Thymine dimer. A kind of DNA damage in which ultraviolet welds two neighboring thymine letters together.
- Ultraviolet filter. An active ingredient of a sunscreen: a chemical or mineral that absorbs or scatters ultraviolet.
- UVA. Ultraviolet light from 315 to 400 nanometers. Most of the ultraviolet reaching the ground, it penetrates deeper and burns only in large doses.
- UVB. Ultraviolet light from 280 to 315 nanometers. It causes most sunburn and drives vitamin D production in the skin.
Statistics
In the FDA's 2019 maximal-use trial, 24 adults who applied sunscreen at 2 mg/cm2 to 75 percent of the body four times a day reached peak blood avobenzone levels of 1.8 to 4.3 ng/mL, depending on the product. 6
In the same 2019 FDA trial, peak blood oxybenzone averaged 169.3 to 209.6 ng/mL across the three products that contained it, against the FDA's threshold of 0.5 ng/mL. 6
All four sunscreens tested on 24 adults in the 2019 FDA trial pushed blood levels of their filters above 0.5 ng/mL on the first day, most people crossing that line within 6 hours of the first application. 6
In the FDA's 2020 follow-up trial on 48 adults, all six filters tested (avobenzone, oxybenzone, octocrylene, homosalate, octisalate, octinoxate) passed 0.5 ng/mL in the blood on day 1 after a single application. 7
In the 2020 FDA trial, peak blood oxybenzone reached 258.1 ng/mL with a lotion and 180.1 ng/mL with an aerosol spray. 7
Oxybenzone was found in 96.8 percent of urine samples from a representative sample of Americans in the 2003-2004 national health survey. 42
In the 2003-2004 US survey, non-Hispanic whites were 6.8 times as likely as non-Hispanic blacks to have urine oxybenzone in the top 5 percent. 42
When 25 volunteers covered their whole bodies twice a day for 5 days with a sunscreen containing 4 percent oxybenzone, they passed 1.2 to 8.7 percent of the applied oxybenzone in their urine, 3.7 percent on average. 76
In 32 volunteers who spread 2 mg/cm2 of a cream with 10 percent each of three filters over the whole body, blood oxybenzone peaked near 200 ng/mL in postmenopausal women and 300 ng/mL in young men. 37
In that week of whole-body sunscreen application, the 32 volunteers' FSH and LH did not change, and only minor differences in testosterone appeared. 37
In breast tissue taken at surgery from 40 women in England, oxybenzone was measured in 83 of 120 samples (69 percent), at up to 26.0 ng per gram of tissue. 49
At least one of four chemical sunscreen filters was found in 101 of 120 breast tissue samples (84 percent) from 40 women. 49
In Danish pregnancies, oxybenzone and its metabolite BP-1 measured about 10 times lower in fetal and cord blood than in the mother's serum. 47
Oxybenzone was found in 23 percent of 79 breast milk samples from Spanish mothers, with a mean of 144.8 ng per gram of milk where it was present. 45
In Danish children aged 3 to 5, urine levels of oxybenzone and two related compounds were statistically higher on a summer day than on a winter day. 77
In US adults aged 20 to 39 in the national health survey, those who said they used sunscreen always or most of the time had 2.61 times the prevalence of antinuclear antibodies of never-users, a cross-sectional finding. 78
In US couples trying to conceive, higher urine levels of the filter benzophenone-2 in either parent went with more girls born, a relative risk for a boy of 0.62 for mothers in the middle third of exposure. 54
In 413 US men whose urine was tested, higher levels of the filter benzophenone-2 went with lower sperm concentration and more immature sperm, an association from urine measurement. 53
Pregnant and nursing rats fed oxybenzone at up to 50,000 ppm in chow had male pups with shorter anogenital distance only at the highest dose, and the authors saw no reproductive harm below 10,000 ppm. 79
Mice given oxybenzone by mouth at 30, 212 or 3000 micrograms per kg a day during pregnancy and nursing had offspring with altered mammary gland growth, which the authors read as disruption even at low doses. 80
Ten years after the Nambour trial ended, 11 new melanomas had been found among people assigned daily sunscreen and 22 among those who used it as they pleased, a hazard ratio of 0.50 on an interval of 0.24 to 1.02. 5
Among 1,031 patients photopatch tested for suspected light-triggered allergy at 30 European centres, 200 (19.4 percent) had at least one photoallergic reaction, with octocrylene, oxybenzone and avobenzone the commonest sunscreen culprits. 81
Of 157 children photopatch tested in Manchester, 6.4 percent had a photoallergic reaction to a UV filter or sunscreen product, most often oxybenzone. 82
A further 5.7 percent of the 157 children tested had an ordinary contact allergy, mostly to their own sunscreen products. 82
In 1,155 patients photopatch tested with sunscreen chemicals at 17 UK, Irish and Dutch centres, 130 (11.3 percent) had allergic reactions. 10
In the UK multicentre series, oxybenzone was the most common photoallergen, with 27 reactions, 21 percent of the total. 10
Of the patients in the UK series found to have a photoallergy, 59 percent had not known they were reacting to a sunscreen chemical. 10
Across 64 industry repeat-insult patch tests of sunscreens with 1 to 6 percent oxybenzone, 48 of 19,570 possible skin responses suggested irritation or sensitization, a rate of 0.26 percent. 62
In those same 64 industry studies, only eight responses were confirmed as contact allergy to oxybenzone, a rate of 0.07 percent. 62
In a 2026 UK multicentre photopatch study, 13 of 132 participants (10 percent) reacted to sunscreen chemicals. 83
Shortening the patch occlusion before light exposure from 48 to 24 hours missed 53 percent of sunscreen photoallergic reactions in the 2026 UK study. 83
Among 156 Italian patients photopatch tested for exposed-site rashes, 13 (8.3 percent) reacted to octocrylene, and 8 of them also reacted to the painkiller gel ketoprofen. 84
Of 23,908 North American patients patch tested for contact dermatitis from 2001 to 2010, 219 (0.9 percent) had a sunscreen identified as the source of an allergy. 61
Among those North American patients allergic to a sunscreen, oxybenzone was the allergen in 70.2 percent when tested at 10 percent strength. 61
In North American patch testing in 2013-2014, the water-soluble filter benzophenone-4 caused a positive reaction in 2.1 percent of patients. 85
Of 2,715 patients photopatch tested in London from 1983 to 1998, only 62 (2.3 percent) had photoallergic reactions, and UV filters caused 52 of the 80 reactions (65 percent). 86
Among 1,000 consecutive first-time dermatology outpatients in Krakow, photoallergic contact dermatitis was confirmed in 15 people (1.5 percent). 87
Tracing a labelled zinc isotope in volunteers who used zinc oxide sunscreen, researchers estimated that at minimum less than 0.01 percent of the applied zinc reached the blood. 40
When nano zinc oxide sunscreen was applied repeatedly to volunteers' skin over 5 days, imaging found no intact particles or toxicity in the living skin layers below. 38
Mice given sunscreen with isotope-labelled zinc oxide on the skin had more of the 68Zn label in their internal organs, and in the livers of their fetuses, than untreated mice. 88
Twenty long-term PABA sunscreen users had a mean blood vitamin D (25-OH-D) of 40.2 nmol/L, against 91.3 nmol/L in matched non-users from the same area. 66
Two of the 20 long-term sunscreen users had blood vitamin D below 20 nmol/L, a level read as deficiency. 66
All 25 Danish volunteers on a one-week sun holiday in the Canary Islands got sunburned at some point, though most used sunscreen. 35
Across the 25 holiday volunteers, sunburn showed up on 202 of 750 body sites checked in real sun. 35
Assuming people spread sunscreen at 0.8 mg/cm2 rather than the 2 mg/cm2 used in testing, a label SPF of 30 gives an effective SPF of about 3.9, by the Danish team's own adjustment. 35
The holiday volunteers took a mean of 9.4 standard erythema doses of UV a day and 57 over the trip, measured by dosimeters worn in real sun. 35
From 1965 to 1968 a Harvard group tested 24 commercial sunscreens and other agents on 175 volunteers in Arizona and the Swiss Alps, and judged 5 percent PABA in alcohol the best. 18
A 5 percent PABA solution had earlier prevented reddening against 25 minimal erythema doses from a solar simulator, yet the skin still tanned after about a week. 19
In Australia, dermatologists began prescribing PABA as a sunscreen in 2 to 5 percent strengths in the 1940s. 89
By 1960 several ready-made PABA sunscreens were on sale over the counter in Australia. 89
Allergy to PABA was discussed at Australian dermatology meetings in 1964 and 1965, starting its slow withdrawal from sunscreens. 89
In 1979 indoor and outdoor tests, a mix of 7 percent padimate O and 3 percent oxybenzone protected against sunburn better than every other formula, including 5 percent PABA. 21
In 29 nickel-allergic volunteers, a low dose of simulated sun cut the skin's allergic response by 35 percent on unprotected skin, and broad-spectrum SPF 10 sunscreens guarded against this better than narrow UVB-only ones. 90
In 18 women given 2 minimal erythema doses from a solar simulator on 4 days, skin with daily SPF 15 had 7 dimer-positive cells per mm2 against 495 in skin whose sunscreen was skipped that day. 33
In that lamp study, skin with daily SPF 15 averaged 7 dimer-positive cells per mm2, no different from skin that was never irradiated. 33
In US national survey data, reported sunscreen use explained 70 percent of the link between income and urine oxybenzone in 2003-2004 and 37 percent in 2005-2006. 91
The filter benzophenone-4 was found in 75 percent of human placentas analysed in Spain, at up to 5.41 ng per gram. 46
Pooling breast milk studies worldwide, oxybenzone levels were more than 20 times higher in European samples than in American ones. 92
In the same pooled analysis, breast milk oxybenzone was more than 50 times higher in samples collected after 2010 than before. 92
In pregnant women across US ECHO cohorts, non-Hispanic Black participants had urine oxybenzone 0.38 times that of non-Hispanic White participants. 93
In 129 Danish children and young people aged 6 to 21, oxybenzone and its metabolite BP-1 were found in more than 80 percent of 24-hour urine samples collected in November. 94
Of 439 Dutch children patch tested for suspected contact allergy, 172 (39 percent) had at least one relevant positive reaction, and reactions to the filter benzophenone-4 had become more frequent than in 1996-2013. 95
In a Chinese cohort followed from 2010 to 2012, higher urine levels of oxybenzone went with smaller testicular volume stage in boys, and the authors linked it to later puberty. 96
In Danish pregnancies, mothers carrying boys who had more of the benzophenone metabolite 4-HBP in their blood had higher thyroid hormone and IGF-I levels, measured in the second trimester. 97
By the authors' calculation, an average US woman would need 34.6 years of daily whole-body application at 2 mg/cm2 of 6 percent oxybenzone sunscreen to match the oxybenzone dose fed to immature rats in an estrogen study, and 277 years at a quarter-body 1 mg/cm2 use. 51
Pooling urine surveys, North Americans had oxybenzone levels about 10 times those of Europeans and 20 times those of Asians. 98
In 1972 lamp tests on 8 subjects, 60 microlitres per square centimetre of 5 percent PABA gave complete protection against 25 minimal erythema doses. 99
In excised human skin under a lamp, three sunscreens claiming UVA protection cut UV-induced free radicals by only about 55 percent at 2 mg/cm2 and about 45 percent at the thinner amounts people commonly apply. 100
In 6 groups of 30 hairless mice exposed to a UVB lamp, 5 percent PABA delayed tumours and reduced both tumour and carcinoma yield. 101
In the hairless mouse model used to test two sunscreens against UV-promoted squamous cell carcinoma, low-dose simulated sun alone produced tumours in 46 percent of mice by week 48. 102
In the Vail split-face trial on 199 skiers in real sun, 40.7 percent had visible redness on the SPF 50 side against 13.6 percent on the SPF 100 side. 36
In 15 nickel-allergic volunteers under a solar simulator, broad-spectrum sunscreens labelled SPF 9 and SPF 24 protected the skin's immune response by factors of 6.5 and more than 25. 103
Of two SPF 15 sunscreens tested on volunteers, the one with high UVA protection had an immune protection factor of 50, more than three times its SPF, while the low-UVA one scored 15. 30
In excised human skin, the filters in commercial adult and children's sunscreens penetrated into the skin at 14 percent of the applied dose, and oxybenzone alone passed through at 10 percent. 104
After a single application of a commercial sunscreen to volunteers, 1 to 2 percent of the applied oxybenzone was passed in the urine over 48 hours. 104
In volunteers given radiolabelled Mexoryl SX (ecamsule) on the skin, urine radioactivity corresponded at most to 0.014 percent of the applied dose. 105
In 6 volunteers who spread a 4 percent 4-MBC sunscreen over 90 percent of the body, blood 4-MBC peaked 6 hours later at 200 pmol/ml in men and 100 pmol/ml in women. 106
After four volunteers covered their bodies with a 10 percent homosalate sunscreen in normal use, the authors' calculated margins of safety for one whole-body application ranged from 11 to 92. 107
Pooling five studies with 857 cases, sunscreen use showed no link with non-melanoma skin cancer, an odds ratio of 0.99 on an interval of 0.62 to 1.57. 34
On the summer sampling day, 53 percent of the Danish kindergarten children had sunscreen put on at the kindergarten. 77
Only 11 percent of the Danish kindergarten children had no sunscreen applied at home or at kindergarten on the summer sampling day. 77
Oxybenzone was detected in the urine of more than 98.5 percent of 1,785 Americans aged 12 to 39 in the national health survey. 108
Of 50 French cases of octocrylene photoallergy, 11 were children, and 24 of 28 adults sensitised by sunscreens had earlier reacted to the painkiller gel ketoprofen. 63
In the 2020 FDA trial, 22 of 23 people using oxybenzone (96 percent) still had blood levels above 0.5 ng/mL on day 21, 17 days after the last application. 7
In the 2020 FDA trial, 42 of 44 avobenzone users (95 percent) were still above 0.5 ng/mL on day 7. 7
In the Gonzalez study, the amount of oxybenzone the 25 volunteers passed in urine did not differ between those given UV light and those who were not. 76
The benzophenone 4-MBP crossed to the fetus more freely, with a median ratio of 1 to 3 between cord blood and the mother's serum. 47
The filter octinoxate was measured in 89 of 120 breast tissue samples (74 percent) from 40 women, at up to 58.7 ng per gram. 49
In the UK series, the commonest reason for testing among patients later found photoallergic was a history of reacting to a sunscreen, at 41 percent. 10
In the Nambour trial, 1,621 adults in Queensland were assigned daily SPF 15-plus sunscreen or their usual habits, and after 4.5 years of real sun, squamous cell carcinoma tumours on the treated skin ran at 1,115 per 100,000 against 1,832, a rate ratio of 0.61. 3
In the same trial, basal cell carcinoma struck 2,588 people per 100,000 in the daily sunscreen group and 2,509 in the discretionary group, a rate ratio of 1.03. 3
Skin aging, graded blind from silicone casts of 903 Nambour participants under 55, progressed 24 percent less in the daily sunscreen group over 4.5 years of real sun, relative odds 0.76. 4
In one Australian summer, solar keratoses rose by 1.0 per person among 588 adults given a base cream and fell by 0.6 among those given SPF 17 sunscreen, with new lesions at a rate ratio of 0.62. 31
French and Swiss students randomly given SPF 30 sunscreen for their holidays spent 72.6 hours in the sun against 58.2 hours for those given SPF 10, and sunbathed 3.1 hours a day against 2.6. 9
The 124 European students in the Autier trials who kept complete records applied a median of 0.39 milligrams of sunscreen per square centimeter on holiday in real sun. 2
Forty-two people applying their own sunscreen all over on a Danish beach used an average of 0.5 milligrams per square centimeter. 1
Over one Australian summer of real sun, blood vitamin D rose by about the same amount in 113 adults using SPF 17 sunscreen as in those using a base cream. 67
Polish holidaymakers who applied SPF 15 sunscreen at a measured 2.4 milligrams per square centimeter for a week in Tenerife raised their vitamin D by 13 to 19 nmol/L, against 28 nmol/L in holidaymakers using sunscreen as they pleased. 68
In a 2013 survey of 4,033 US adults, 42.6 percent of women and 18.1 percent of men said they regularly used sunscreen on the face when outside for an hour or more on a warm sunny day. 8
In the same survey, nearly 40 percent of sunscreen users were unsure whether their product gave broad-spectrum protection. 8