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expert reaction to study looking at sunscreen ingredients and bloodstream concentrations

Research published in JAMA demonstrates that some ingredients from sunscreens are absorbed into the blood and there is a need need for further studies to determine the clinical significance of these findings.

Prof Brian Diffey, Emeritus Professor of Photobiology, Dermatological Sciences, Newcastle University, said:

“As the authors themselves have said, this was a maximal use study using generous and frequent applications of sunscreen – in practice most people apply a thinner layer of sunscreen over a smaller fraction of the body surface less often during the day, resulting in a daily amount of sunscreen about one tenth of the amount used in this study.

“This would mean that for 3 of the 4 agents studied here, the levels of active ingredients found in the plasma during typical usage would fall below the threshold value.  (The threshold value in toxicology means the value that would approximate the highest plasma level below which the carcinogenic risk of any unknown compound would be less than 1 in 100,000 after a single dose.)

“The authors suggest their findings mean we should do further to determine the clinical significance of these findings.  It is important to note there is no evidence from this study that there is any health risk.  And even at maximal use, any theoretical risk is almost certainly far smaller than the reduced risk of skin cancer that has been shown to be associated with sunscreen use.  Indeed, the authors themselves say that their results do not suggest that people should refrain from using sunscreen.

“It is important to note that each participant in the study applied the equivalent of two standard bottles of sunscreen over four days.  This is considerably greater than typical use where it has been estimated that people who use sunscreen go through about one bottle per year per person.”

Prof Dorothy Bennett, Director of the Molecular and Clinical Sciences Research Institute, St. George’s, University of London, said:

Please note: my expertise is in skin cancer and UV light rather than toxicology. However I can understand the article and the analysis.

“The editorial appears to comment in a fair way on the limitations of the study.  The press notice seems a reasonable summary and the science looks reliable.

“The researchers tested the concentrations of four particular chemicals in the blood (plasma) of volunteers who had used sunscreens in amounts within ranges recommended by manufacturers.  The chemicals were present in the sunscreens or some of them, and the idea was to test how much is absorbed through the skin.

“The point of the article is that the blood levels of all four compounds exceeded the level above which the US government body (Food and Drug Administration, FDA), recommends that companies should test whether there are any toxic effects.  That threshold level is 0.5 ng/ml.  1 ng (nanogram) is a millionth of a milligram (mg).  In almost all volunteers, all the tested compounds reached blood levels higher than that, sometimes much higher, after even a single day of sunscreen use.

“It does not mean that the chemicals are toxic, but that we don’t know and the FDA recommends that it should be checked whether they are toxic.  According to the editorial, the FDA has already tried and failed to get sunscreen manufacturers to do toxicity testing.

“It remains important to avoid excessive sun exposure, as there is strong evidence that ultraviolet light is the main cause of skin cancer including melanoma.  This study is no immediate cause for alarm, but the alternatives to sunscreen are using clothing to screen the skin from the sun, or limiting the amount of time in the sun.  It should also be remembered that a little sun exposure is good for us, allowing vitamin D to be made by the skin.  A rough guide to how much sun is ‘not too much’ for your skin type is the amount where you don’t get sunburn.”

Dr Andrew Birnie, British Association of Dermatologists, said:

“It’s worth noting that the amounts of sunscreen used in this study are significantly higher than the average person would use in normal circumstances.  Furthermore, sunscreen has been used by a large portion of the population for a number of decades and there has not been any epidemiological data that suggests users come to harm.  We agree with the researchers that people should not make the knee-jerk decision to stop using sunscreen.

“Skin cancer is the UK’s most common cancer, equalling all other cancers combined.  The link between excess sun exposure and skin cancer is well documented and indisputable.  This research on sunscreen is very much at an early stage.  The first line of defence against the sun should be shade and clothing, with sunscreen used for additional protection.”

Prof Rob Chilcott, Head of Toxicology, University of Hertfordshire, said:

“The results of this study are unsurprising as the skin is not a perfect barrier and so absorption of chemicals from sunscreens, and indeed other skin products such as cosmetics, is to be expected.  This does not mean that chemicals used in the sunscreens are unsafe, but that further studies are required to confirm their classification as “Generally Recognised as Safe and Effective”.

“This study is a positive finding in that it will ensure that sunscreens undergo more rigorous testing in the future.  In the meantime, it should be emphasised that the health benefits of using sunscreens are well established and far outweigh the risks associated with the low-level absorption of their chemical constituents.”

Prof Sir Colin Berry, Emeritus Professor of Pathology, Queen Mary University of London, said:

“First “The demonstration of systemic absorption well above the FDA guideline does not mean these ingredients are unsafe” is correct and what follows (the next sentence in the editorial) is not justified from the data that the authors present.  To suggest the extensive pattern of study which the authors indicate requires “that testing under actual use conditions will be paramount” would be a far more sensible first step to determine whether there is a real problem here.

“Second, it is not the case that testing programs deal with all eventualities – many skin- applied medications have comments about eczema, psoriasis etc. that make clear that variability in penetration is important; for renal disease a general warning about dose is given rather than setting up a series of tests in those affected.”

‘Effect of sunscreen application under maximal use conditions on plasma concentration of sunscreen active ingredients’ by Murali K. Matta et al. was published in JAMA at 16:00 UK time on Monday 6 May 2019.

Declared interests

Prof Brian Diffey: “I invented both the UVA Star Rating for sunscreens in conjunction with Boots in the UK, and the Critical Wavelength adopted by the Food & Drug Administration in the USA as the sole measure of broad spectrum protection.”

Prof Dorothy Bennett: “I declare no vested interests.”

Dr Andrew Birnie: “Dr Birnie is a Consultant Dermatologist and skin cancer surgeon in the NHS.  He is also Director at Altruist Medical, which creates affordable sunscreen and supports charities that help children with albinism in Tanzania and the rest of Africa.”

Prof Rob Chilcott: “None.”

Prof Sir Colin Berry: “I have no professional links to sun-screen firms or the cosmetic industry.”

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