That’s the conclusion of a new study from the Center for Drug Evaluation and Research, part of the US Food and Drug Administration.

There are two basic types of sunscreen. Mineral sunscreens sit on top of the skin and reflect the rays away. Chemical sunscreen are designed to be absorbed into the skin. Sunscreens are still considered effective as part of a multifaceted approach to sun protection that includes protective clothing sunglasses, seeking shade and staying out of the sun when it is at its most fierce. But the chemicals in many sunscreens continue to be concerning – not least of which because they are so poorly studied.

The FDA findings, published in the medical journal JAMA, build on those of a pilot study published by the agency in 2019. That study, looked at four popular chemical sunscreens – avobenzone, oxybenzone, octocrylene, and ecamsule – were absorbed from the skin into the bloodstream after a single day of use.

The new study reevaluated three of the original four (avobenzone, oxybenzone and octocrylene) and added three additional sunscreen chemicals – homosalate, octisalate, and octinoxate.

And randomly assigned 48 volunteers (average age of 38.7 years; 50% women; 48% white) to apply sunscreen that contained one or more of these sunscreening chemicals via an aerosol spray, lotion, nonaerosol spray or pump spray.

High levels of absorption

Sunscreen was applied to 75% of body surface area over 4 days. It was applied in the exact same amount once on day 1 and four times during the remaining 3 days at 2-hour intervals.

The study was conducted in doors. Although conducting the study outside would be more indicative of a real-life setting, the researchers conducted the study indoors, noting that “the data would have likely been more variable because of the need to control for heat, humidity, wind and cloud cover.”

Blood samples collected and analysed over the study and found that the average plasma concentrations of all six active ingredients were greater than 0.5 ng/mL after a single application on day 1 – higher than recommended safe levels for these chemicals.

After day 1, the concentration of the six chemicals in the blood increased each day of application, and remained above FDA safety levels at day seven, well after application had ended. Two of the chemicals – homosalate and oxybenzone – remained well above safety thresholds 21 days after the first application.

No safety tests

Researchers went out of their way to stress that the fact that an ingredient is absorbed through the skin and into the body doesn’t mean it is unsafe, said Dr. Janet Woodcock, director of the Center for Drug Evaluation and Research, the arm of the FDA which conducted the studies.

“Rather, this finding calls for further industry testing to determine the safety and effect of systemic exposure of sunscreen ingredients, especially with chronic use,” Woodcock said.

Nevertheless these are chemicals – many of them hormone disrupting – that should not be in the body in any quantity. The fact that they remained in the body even after the trial was stopped suggests

Commenting on the study David Andrews, a senior scientist for the Environmental Working Group (EWG), a consumer organization which advocates for sunscreen safety, said

“What is most alarming about these findings is that chemicals are absorbing into the body in significant amounts and the ingredients have not been fully tested for safety,”

He added: “If companies want to keep these ingredients in products, they need to urgently test for potential harm to children and harm from long-term use.”

• For sunsafe tips see our article: Healthy habits in the sun

That’s the conclusion of a small study conducted by researchers at the US Food and Drug Administration (FDA).

The 23 volunteers tested four sunscreens, including sprays, lotion and cream, applying the formulations to 75% of the body four times a day over four days. This regimen was chosen because it is in line with standard manufacturers’ instructions to apply sunscreen at least every 2 hours during the day.

The researchers used blood tests to determine the maximum levels of certain chemicals absorbed into the bloodstream.

The results, published in the Journal of the American Medical Association (JAMA), found that chemical levels in the blood began to rise on the first day of use and, with continuing use of the sunscreens, the levels of sunscreen chemicals detected in the blood also continued to rise, suggesting that these chemicals may accumulate in the blood over time.

Maximum plasma levels of the chemicals it tested for – avobenzone, oxybenzone, octocrylene and, in one sunscreen, ecamsule – were well above the level of 0.5 nanograms per millilitre (ng/mL) at which FDA guidelines call for further safety testing.

FDA calls for further testing

Commenting on the study on its website, the FDA said: “The fact that an ingredient is absorbed through the skin and into the body does not mean the ingredient is unsafe. Rather, this finding calls for further testing to determine the safety of that ingredient for repeated use. Such testing is part of the standard pre-market safety evaluation of most chronically administered drugs with appreciable systemic absorption.”

The Agency suggested that since it began regulating sunscreens in the 1970s, its understanding of drug absorption through the skin and the ability to measure drug absorption have advanced. It’s not entirely clear if human safety testing has kept up with this evolving understanding, however. In fact, sunscreen creams have largely avoided extensive safety tests because absorption had previously been thought to be minimal.

Hormone disruption

The findings could hardly have been a surprise. The authors note, for example, that past studies have found oxybenzone and octocrylene have been found in human breast milk. Oxybenzone has also been identified in urine, blood and amniotic fluid.

Animal studies have raised concerns that the chemicals, oxybenzone in particular, might disrupt normal hormone patterns in people, the researchers noted in their study. We have previously reported on research showing that chemical sunscreening agents called benzophenones may raise the risk of developing endometriosis and may also contribute to male infertility. But overall  there is very little study of how these chemicals behave in the body of adults or children.

Stick to mineral formulations

Most sunscreens on the shelf use chemicals like oxybenzone, avobenzone and octocrylene to block harmful rays. These chemicals absorb ultraviolet radiation and convert it into a small amount of heat.

If you are concerned about the safety of conventional chemical sunscreens try swapping to mineral sunscreens and more natural formulations. These rely on zinc oxide and titanium dioxide, which reflect sunlight from the skin, rather than absorbing it. Natural and organic formulations will also have fewer worrying ingredients like parabens.

• For more on how to take the best care of your skin when the sun is out see our article Summer skin care – it’s as easy as 1-2-3

In a study published in Science Advances, researchers from the University of California San Diego, School of Medicine reveal a potential new role for some bacteria on the skin: protecting against cancer.

“We have identified a strain of Staphylococcus epidermidis, common on healthy human skin, that exerts a selective ability to inhibit the growth of some cancers,” said Richard Gallo, MD, PhD, Distinguished Professor and chair of the Department of Dermatology at UC San Diego School of Medicine. “This unique strain of skin bacteria produces a chemical that kills several types of cancer cells but does not appear to be toxic to normal cells.”

Blocking tumour development

Using an animal model the team discovered the S. epidermidis strain produces the chemical compound 6-N-hydroxyaminopurine (6-HAP). Mice with an S. epidermidis strain on their skin that did not make 6-HAP had many skin tumours after being exposed to ultraviolet rays (UV), but mice with the S. epidermidis strain producing 6-HAP did not.

In addition to its potential to suppress development of UV-induced skin tumours, 6-HAP also impairs the creation of DNA, known as DNA synthesis, and prevents the spread of transformed tumour cells.

For instance, the animals that received intravenous injections of 6-HAP every 48 hours over a two-week period experienced no apparent toxic effects, but when transplanted with melanoma cells, their tumour size was suppressed by more than 50% compared to controls.

A layer of protection

“There is increasing evidence that the skin microbiome is an important element of human health. In fact, we previously reported that some bacteria on our skin produce antimicrobial peptides that defend against pathogenic bacteria such as, Staph aureus,” said Gallo.

In the case of S. epidermidis, it appears to also be adding a layer of protection against some forms of cancer, said Gallo. Further studies are needed to understand how 6-HAP is produced, if it can be used for prevention of cancer or if loss of 6-HAP increases cancer risk, said Gallo.

While Staphylococcus epidermidis is commonly found on human skin, the team say about 20% of the healthy population is likely to have a strain which produces 6-HAP. “Our study found that it is common, but not on everyone,” said Gallo.

A global, personal, ecological issue

Globally, one in every three cancers diagnosed is a skin cancer and currently, between 2 and 3 million non-melanoma skin cancers and 132,000 melanoma skin cancers – typically caused by overexposure to the sun’s UV rays – are diagnosed each year. Melanoma is the most serious form of skin cancer that starts in the pigment-producing skin cells, called melanocytes.

Increasing levels of skin cancer are a lifestyle issue – for instance, with people not taking sun safety seriously. According to the World Health Organization, sunbed use is estimated to be responsible for more than 450 000 non-melanoma skin cancer cases and more than 10 000 melanoma cases each year in the United States of America, Europe and Australia combined.

But skin cancer rate can rise due to ecological problems as well. As ozone levels are depleted, the atmosphere loses more and more of its protective filter function and more solar UV radiation reaches the Earth’s surface. It is estimated that a 10 per cent decrease in ozone levels will result in an additional 300,000 non-melanoma and 4,500 melanoma skin cancer cases each year.

The current study shows that skin has an innate ability to protect us from skin cancer – the questions left open are why don’t more of us have this strain on our skin and what might interferes with growth of beneficial strains of S. epidermidis. We know that harsh and/or antibacterial soaps and body washes, as well as antiperspirants, affect skin flora – but their specific effect on S. epidermis and other beneficial skin bacteria is poorly researched. The type of clothing we wear (for instance whether it is breathable or coated with anti-stain, antibacterial chemicals) may have an effect as will our use and exposure to antibiotics.

Too often we focus on ‘beauty’ – fewer wrinkles, fewer spots, etc – when it comes to skin health. A better understanding of how the skin’s natural microbiome interacts with its environment may be a better route to truly healthier skin.

In recent years, probiotics have become synonymous with helping maintain good digestive health. Whether as live active cultures found in some yogurts or as daily supplements, probiotics are live, “friendly” bacteria that may benefit a person’s health.

Now, emerging research is suggesting that the benefits of probiotics may extend beyond the digestive tract to the skin. In fact, skin prone to acne or rosacea has shown improvement with daily probiotic use, giving dermatologists reason to consider supplementing traditional acne therapy with a dose of beneficial bacteria.

Working at a genetic level

In a recent pilot study, published in the journal Beneficial Microbes, researchers followed two small groups of people over a 12-week period

One consumed a liquid supplement (75mg/day) containing Lactobacillus rhamnosus​ SP1 (LSP1) at a dose of 3 billion ​colony forming units (CFU) per day. A placebo group of 10 subjects received a liquid containing no probiotics.

The choice to study LSP1 was based on previous evidence​​ identifying the strain’s effectiveness in improving leaky gut/dysbiosis.

Skin biopsies taken at the beginning and end of the study period were analysed for two things: the gene expression of insulin-like growth factor 1 (IGF1​) and forkhead box protein O1 (FOXO1​).

Based on physicians using a standard five-point scale for rating improvement in skin appearance, those taking the probiotic were 28% more likely to be improved/markedly improved (versus worsened or unchanged) compared with the placebo group.

A gut-skin axis?

The probiotic group in addition showed a 32% reduction and a 65% increase in IGF1 and FOXO1 gene expression in the skin, respectively. Gene expression is the way genes function to switch certain body functions, such as hormones, on or off.

This, say the scientists, shows that that supplementation with LSP1 was able to normalises skin expression of genes involved in insulin signalling and improves the appearance of adult acne.

“It is possible that this probiotic strain may improve insulin resistance through direct metabolic effects and/or by correcting a state of intestinal dysbiosis,”​ the study’s authors theorised.

“Alterations in the gut microbiome and gut permeability can increase levels of circulating toxin that in turn activate proteins (TLR-2 and TLR-4) that play a key role in the innate immune system. Their activation can induce the release of cell-signalling molecules and the expression of enzymes that ultimately aggravate acne.”​

According to the authors, the effect of the probiotics on gene expression in the skin, which needs to be confirmed by other studies, suggests the existence of a gut-skin axis (similar to the well-established gut-brain axis) in which skin physiology is affected by specific bacterial strains in the gastrointestinal tract.

The study by Japanese researchers involved 60 healthy men and women between 22 and 59 years of age. Participants were divided in three, with subjects given either a placebo, or a hyaluronic acid (hyaluronan, or HA) formulation using one of two varieties, with a molecular weight of 2k or 300k. Researchers used Hyabest (S)LF-P (from the Japan-based Kewpie Corporation, which also funded the study). The dosage, 120 mg daily, was the same for all, and the trial lasted 12 weeks.

Within two weeks of completing the course of supplementation, subjects were observed with instrumentation and interviewed via questionnaire. The HA groups reported indisputable changes in the depth and definition of wrinkles, which was substantiated by microphotography, along with notable improvements in the lustre and suppleness of the skin.

Essential for skin

The skin contains about 50% of the body’s hyaluronan (HA), a component present in every connective tissue. Degradation of HA and collagen is reported to be a cause of wrinkles, with many ingredient suppliers exploring the potential of supplementation to improve skin health from within.

Despite the interest in hyaluronan, there have only been a handful of clinical trials investigating the efficacy of oral consumption of HA on skin health and ageing.

Adding to the data

The new analysis cited several other Japanese studies that evaluated the compound’s efficacy. One  found that people with rough and dry skin who took 240 mg of HA daily experienced significant improvements in dry skin on the face and body after just 6 weeks of supplementation.

For instance in a 2014 study published in Nutrition Journal, daily intake of Hyabest (S)LF-P was shown to counter the loss of skin hydration and guard against deterioration due to age, and to such environmental factors as cold, dry air and UV radiation. For the first time, daily oral intake of hyaluronic acid, which had been used topically from its debut in the 1930’s, was determined to be a viable means of replenishment in the body.

While this latest study adds to this body of evidence on HA and skin ageing, the researchers note that HA supplements can be poorly absorbed “and once in the body, its effectiveness is diminished by absorption in the intestinal tract and metabolic action by the liver.” While the molecular weight of the HA supplement made little difference its level of bioavailability might. Taking formulas designed not to degrade so rapidly once ingested will likely lead to better results, they add.

Urtica thunbergiana is a member of the nettle family found in Japan, China and Taiwan. It is a common ingredient in traditional Chinese medicine and the young leaves are nutritious and can be used in cooking. The skin protecting component, say researchers is the phenolic compound chlorogenic acid.

“Although the antioxidant potential of Urtica species is well known, the protective effects of U. thunbergiana against UVB-irradiated photoaging have not been explored,” the researchers wrote in their study, published in the Journal of Functional Foods.

Its close relative, the stinging nettle (U. dioica), has already been shown to have multiple health benefits including an anti-inflammatory effect that aids muscles and joints but also eczema to arthritis, and anti-cancer properties.

Though U. thunbergiana as a plant doesn’t have the same amount of research behind it, there is laboratory evidence to show that chlorogenic acid, which is also present in stinging nettles and green coffee beans, has some beneficial dermatological effects such as reducing skin redness caused by excess ultraviolet exposure and (in tests with green coffee beans) helping to maintain skin hydration.

Anti-photoaging effects

The scientists looked at U. thunbergiana’s anti-photoaging effects  by examining collagen synthesis human skin cells, as well as examining the anti-oxidant and protective effects of ingesting the plant extract on mice.

The animals were divided into four groups two of which consumed a normal diet (control mice), one which was supplemented with 0.1% U. thunbergiana via their water and on which was supplemented with  1% U. thunbergiana.

One of the control groups was kept away from UV radiation, the other three were exposed ultraviolet B lights three times a week for nine weeks.

UVB-epxosed skin showed signs of  decreased skin hydration and increased skin reddening (erythema) compared to the non-exposed skin. But in the mice supplemented with the botanical extract skin fared better showing better skin hydration, moisture levels, and a more youthful appearance.

The 0.1% supplement increased skin hydration by 142% and the 1% supplement by 172%

Boosting collagen too
Additionally, the researchers found that in ultraviolet B-exposed skin, collagen fibers were irregular and disorganized; however, in the supplemented groups, their density was increased. These effects, they say were due to the two active phenolic compounds, caffeic acid and chlorogenic acid, the researchers said.

U. thunbergiana, they say shows real promise in in beauty-from-within dietary supplements or functional foods, though more research is needed.

Urtica thunbergiana supplements are not yet common but green coffee and nettle supplement are widely available as capsules, pills and tinctures. For tips on how to cook with nettles see our feature We love nettles! Three great spring detox recipes.

In a study published in the journal Scientific Reports Researchers fed mice a diet of 10% whole tomato powder daily for 35 weeks, then exposed them to intense periods of ultraviolet light.

There was a 50% decrease in skin tumours in male mice, compared to those that ate no dehydrated tomato. Previous research has shown that male mice develop tumours earlier after UV exposure and that their tumours are more numerous, larger and more aggressive.

There were no significant difference in tumours numbers for the female mice in the study –  the paper does not define what ‘significant’ means, but does suggest that overall the female mice had so few tumours that it was difficult to judge the true impact.

“This study showed us that we do need to consider sex when exploring different preventive strategies,” said the study’s senior author, Tatiana Oberyszyn, professor of pathology and member of Ohio State’s Comprehensive Cancer Center.

“What works in men may not always work equally well in women and vice versa.”

Another possibility, however, is that tomatoes may be particularly effective in those who are at higher risk of skin cancer.

A common cancer

Because they are common and usually non-fatal non-melanoma skin cancers are usually excluded from tables listing the incidence of skin cancer.

However, it is widely recognised that non-melanoma skin cancers are the most common of all cancers. Official reporting of non-melanoma cancers is poor but it is believed that there are more new cases each year than breast, prostate, lung and colon cancers combined.

Despite a low mortality rate, these cancers are costly and can be disfiguring.

Human studies

Previous human clinical trials suggest that eating tomato paste over time can protect against sunburn, likely due to their carotenoids content. Similarly, supplements of lycopene and lutein have been shown to be protective.

Carotenoids are fairly quickly deposited in the skin of humans after eating, and may be able to protect against UV light damage, said Jessica Cooperstone, co-author of the study and a research scientist in the Department of Food Science and Technology in the College of Food, Agricultural, and Environmental Sciences at Ohio State

“Lycopene, the primary carotenoid in tomatoes, has been shown to be the most effective antioxidant of these pigments,” she said.

In the diet, lycopene is more bioavailable in cooked/processed tomato products and in one 2001 study, people who added 40g of tomato paste and 10g of olive oil to their main meal for ten weeks showed a 40% reduction in sunburn levels compared to people who added 10g of olive oil but no tomato paste.

A 2008 study estimated the equivalent SPF of consuming five tablespoons (55g) of standard tomato paste with 10g of olive oil every day to be around 1.3. That may sound small, but the SPF scale is not linear.

An SPF of 2 (the lowest you can find on the marketplace) blocks around 50% of UVB. An SPF of 1.3 would block around 20%. So while eating more tomatoes may not prevent all burning and sun damage, getting more lycopene increasingly looks like a good way of protecting your skin from within against premature skin ageing due to sun damage.

But new research from Japan suggests it may also have properties which help maintain healthy circulation and skin elasticity

Japanese scientists were looking for food and plant substances that could inhibit the formation advanced glycation end-products (AGEs), by-products of metabolism that are associated with increased oxidative stress and inflammation. In particular the AGE pentosidine increases with age and correlates with the degree of skin and artery stiffness. Yellowing skin associated with ageing also may be due partly to glycation.

The first step was to evaluate 681 plant extracts for antiglycation activity. Among the 22 possible candidate plants, 17 species exhibited higher activity against pentosidine than the antiglycation agent aminoguanidine.

Four of these (rosemary, thyme, cat’s whispers and lemon balm) belonged to the Lamiaceae family and were rich in the AGE fighting substance, rosmarinic acid. The researchers chose to study lemon balm because of its safety, taste, stable supply, and adaptability to beverage form.

Objective evidence

The next step was to study the benefits of lemon balm in people. The scientists divided a group of 28 people, men and women, into two groups. One group was given barley tea as a control substance. The other was given lemon balm tea (made using 3.23g tea bags which they were instructed to brew in 200ml of water for 5 mins). Participants did not take any other herbs during the trial.

The researchers were looking for evidence of suppressed glycation-associated reactions in tissues as well as things like skin colouration and elasticity.

Although the paper does not say how much tea was drunk daily, it does suggest that those who had a higher intake benefitted more.

For example, the more lemon balm tea the participation drank each day the more resistant the collagen and elastin fibres in their tissues were to the degenerative effects of AGEs.

After 6 weeks arterial stiffness – as measured by brachial-ankle pulse wave velocity (baPWV) – was lower in the lemon balm group – but not in the barley tea group, though there were no differences in either systolic or diastolic blood pressure between the groups.

Objective testing showed that skin colour improved in the lemon balm group compared to the barley tea group. In addition skin elasticity improved slightly in the lemon balm group – but only in the women.

Although a small study the findings are encouraging suggesting that daily lemon balm tea, and specifically the rosmarinic acid it contains, is a pleasant and effective way to improve arterial health and circulation that that these improvements that can be observed through healthier looking skin.

• For more on the benefits of lemon balm see our article Lovely, lovely lemon balm

In a recent research paper, the use of curcumin after burns and scalds were found to reduce the severity of the injury, lessen pain and inflammation, and improve healing with less than expected scarring, or even no scarring, of the affected skin.

Writing in the journal BioDiscovery, Dr. Madalene Heng, Clinical Professor of Dermatology at the David Geffen School of Medicine, in California, reports on her experience using curcumin gel on such injuries using three examples of patients treated after burns and scalds, and provides a detailed explanation why topical curcumin may work on such injuries.

She stresses that use of topical curcumin gel for treating skin problems, like burns and scalds, is very different, and appears to work more effectively, compared to taking curcumin tablets by mouth for other conditions.

When taken by mouth, curcumin can be poorly absorbed into the body, she says, and therefore might not work as well.

A traditional remedy

Curcumin is an ingredient found in the common spice turmeric. Turmeric has been used as a spice for centuries in many Eastern countries and gives well known dishes, such as curry, their typical yellow-gold colour. The spice has also been used for cosmetic and medical purposes for just as long in these countries.

In recent years, the medicinal value of curcumin has been the subject of intense scientific studies, with publication numbering in the thousands, looking into the possible beneficial effects of this natural product on many kinds of affliction in humans.

A potent anti-inflammatory

Heng believes that the effectiveness of curcumin gel on the skin – or topical curcumin – is related to its potent anti-inflammatory activity. Based on studies that she has done both in the laboratory and in patients over 25 years, she believes the key to curcumin’s effectiveness on burns and scalds is that it is a natural inhibitor of an enzyme called phosphorylase kinase, which has many important functions, including its involvement in wound healing.

Wound healing is the vital process that enables healing of tissues after injury. The process, which begins with the release of phosphorylase kinase about 5 minutes after an injury, goes through a sequence of acute and chronic inflammatory events, during which there is redness, swelling, pain and then healing, often with scarring in the case of burns and scalds of the skin.

Dr. Heng says she uses curcumin gel for burns, scalds and other skin conditions as complementary treatment, in addition to standard treatment usually recommended for such conditions.

Most of us look for high SPF sunscreens that will minimise the damage caused by long periods of sun exposure. But as we have previously reported many of the chemicals in sunscreens have hormone disrupting properties that could threaten human health.

Now legislators in Hawaii are seeking to ban the sunscreening chemicals oxybenzone and octinoxate in their state due to evidence of harm to the natural environment.

At the end of January the House Committee on Energy and Environmental Protection passed House Bill 600, introduced by Representative Nicole Lowen (District 6, Kailua-Kona, Holualoa). If the ban becomes law, sunscreens with these chemicals will no longer be on sale in Hawaii.

At the same time the Committee also moved other proposed legislation, House Bill 819 forward. This bill would allow continued sale of oxybenzone products, but impose new labelling requirements.

Whatever the outcome Hawaii’s war on oxybenzone has implications for legislation elsewhere in the US and the world.

In November 2015, a group of MEPs proposed a motion to ban oxybenzone in cosmetic products throughout the European Union. That legislation, however, did not progress. Should the Hawaiian bill become law, however, it is likely such calls will be renewed in Europe.

Widespread use

Oxybenzone (also known as benzophenone-3 or BP3) is one of the most widely used UVA filters. In addition to blocking UVA, it also absorbs UVB and it is this quality that makes oxybenzone very attractive to cosmetics manufacturers. Today it can be found an over 3500 products worldwide, including  hairsprays, cosmetics and nail polishes as well sunscreen preparations.

In humans it is a known endocrine disrupter, but its potential for harm doesn’t stop there. The compound has been found entering the environment both through wastewater effluent and directly from swimmers wearing sunscreens. Each year, it is estimated that around 6,000 to 14,000 tonnes of sunscreen cream (or lotion) enters the world’s oceans.

An aquatic poison

Initial studies of oxybenzone in suntan products have indicated that it harms corals in the sensitive periods of their life cycle.

A 2008 study, for example, found that oxybenzone is likely to cause coral bleaching both in the lab and in the wild in several tropical regions. Other studies have suggested that oxybenzone also acts as an endocrine disruptor among marine creatures such as shrimps and clams.

In 2015 a study from a team of international scientists has found oxybenzone was highly toxic to juvenile corals and other marine life. In particular exposing the baby corals to oxybenzone damages their DNA and acts as an endocrine disruptor, which eventually cases them to die. The study also indicated oxybenzone induces coral bleaching.

Concentrations of the chemical in the waters around Hawaii were between 800 parts per trillion and 19 parts per billion, according to the study, and the lowest concentration to see toxicity effect is 62 parts per trillion. In plain English, that’s equivalent to one drop in 6.5 Olympic swimming pools.

In previous research, in some parts of Hawaii and the US Virgin Islands scientists have measured levels as high as 1,400,000 parts per trillion. That’s more than 20,000 times higher than known toxic levels.

Big brands deny harm

Some brands already sell environmentally- or reef-friendly sunscreens without known harmful chemicals like oxybenzone.

But perhaps not surprisingly big manufacturers like L’Oreal dispute the link between oxybenzone and coral bleaching. Commenting in an article in Scientific American, Marc Leonard, head of L’Oréal’s Research & Innovation, Environmental Research department in Aulnay-sous-Bois, France, said:

“Regulatory decisions have to be made on sound scientific evidence and multiple studies. They have to be completed by different teams to provide a significant bundle of evidence. We are very far from it in this case.”

L’Oréal is, nevertheless, working on making sunscreen products without oxybenzone, in anticipation of a possible ban – or bans.

• Neals’ Yard Remedies sunscreens do not contain oxybenzone.
• For more on sunscreens see our article Healthy habits in the sun.