Sunscreen is one of the most effective ways to enjoy the sun while also protecting yourself against painful burns and the long-term risk of skin cancer.
Sunscreens contain ingredients that absorb ultraviolet rays before reaching the skin, dispersing them through a chemical process.
These products, which are also referred to as organic or synthetic sunscreens, are absorbed into the skin.
Whereas a mineral sunscreen, which contains chemicals such as zinc oxide or titanium dioxide, forms a physical barrier to the sun’s rays.
Mineral sunscreens have been marketed as a better option for persons with sensitive skin, such as children, who are susceptible to chemical discomfort.
Experts around the world recommend people should use sunscreen but, according to a new study, should be careful about combining or mixing different products.
Academics at the University of Oregon and the University of Leeds evaluated various SPF 15 sunscreen formulations created using chemicals permitted for use in the United States and the European Union.
They measured the mixtures’ UVA protection, which is one type of UV radiation; the other type is UVB.
While UVB is the most common type of UV that causes skin cancer, both types of UV have the potential to cause cancer.
The researchers were particularly concerned about one blend whose formula matched the most sun cream formulations used in the EU and US.
After two hours of exposure, they discovered that it lost 90% of its UVA protection when combined with 6% zinc oxide.
In comparison, when the recipe was exposed to UV for two hours without the zinc oxide, the formula’s protective efficacy was reduced by only 16%.
When exposed to light, the zinc oxide destroyed the other UV-absorbing compounds in the mixture, diminishing their protective properties.
Richard Blackburn, co-author of the study, urged users to continue using sunscreen but to take precautions when combining multiple items.
“We still recommend consumers use sunscreen but suggest they should be careful to avoid mixing sunscreen with zinc oxide, whether intentionally with hybrid sunscreens that combine small-molecule UV filters with zinc oxide, or incidentally by mixing sunscreen with other products containing zinc oxide, such as makeup containing SPF,” he said.
Additionally, the study, published in Photochemical & Photobiological Sciences, discovered that the combination sunscreens were more dangerous when exposed to sunlight in experiments on zebra fish embryos.
Fish embryos exposed to a sunscreen mixture containing zinc oxide developed abnormally, with underdeveloped fins and shorter bodies, compared to those exposed to other sunscreens.
However, when fish embryos were exposed to simply zinc oxide, they did not exhibit the same response.
This indicated that the toxicity was caused by the combination of the zinc and the other compounds, the experts added.
They acknowledged that their findings are limited since they did not use the identical sunscreen formulations used by manufacturers.
Additionally, the team stated that chemicals, perfumes, and preservatives used in high-street products may react differently.
They acknowledged in the journal that additional research is needed to determine how different creams function under various settings and in combination.
Dr Emma Wedgeworth, the spokeswoman for the British Skin Foundation and a dermatologist, welcomed the study.
She said, however, that people should bear in mind that sunscreen had been demonstrated to protect against skin cancer and lacked proof that it was dangerous to humans.
“We are lucky enough to have high quality standards and rigorous testing of sunscreen products available in the UK and used, as per the instructions, I am confident that it offers very high protection against damaging UV rays,” she said.
“To date, there is still no evidence that sunscreen is toxic to humans and it is difficult to extrapolate studies in zebra fish embryos to a real life situation of sunscreen usage.”
Other scientists concurred with Dr Wedgeworth’s observations.
Professor Winston Morgan, a toxicologist at the University of East London, expressed concern about the public’s knee-jerk reaction to the study.
“My concern is that the public may see headlines from this study warning about sunscreen mixing and think that all sunscreens are not safe which would be wrong and counterproductive,” he said.
Professor Oliver Jones, a chemical expert at RMIT University in Melbourne, Australia, lauded the work as ‘thought provoking’ as well.
However, he cautioned against reading too much into the findings with zebra fish embryos.
“While this is a well-used model for ecological toxicity testing, zebrafish embryos are not mini humans, and the results are not directly comparable,” he said.
“I think the risk of UV damage from not using any sunscreen at all is higher than even the worst-case scenario in this study. So in short, don’t panic and keep using sunscreen.”
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