After only two hours of sun exposure, some sunscreens offer very limited protection against ultraviolet rays and can even be dangerous for the skin.
- Commercial sunscreens contain zinc oxide, a mineral that is safe and effective against the sun’s ultraviolet rays when tested alone.
- But when exposed to sunlight, zinc oxide reacts with the other ingredients and decreases the effectiveness of sunscreen filters in sunscreen by up to 90%.
- Zinc oxide is also at the origin of an increase in the toxicity of the formula of sun creams.
Widely used in summer to protect us against UV rays and avoid sunburn, sunscreens are once again singled out. Already accused of participating in the destruction of marine ecosystems, sun protection products would not be, according to this new study, as effective and safe for us as we thought so far.
Led by researchers from the University of Leeds (England), the University of Oregon, and Oregon State University (USA), this new study reveals that chemical reactions involving one of the main active ingredients in creams, zinc oxide, reduces their effectiveness after two hours of exposure. Worse, creams containing zinc oxide could be dangerous for your health. The study is published in the journal Photochemical and Photobiological Sciences.
The zinc oxide in question
Currently, the effectiveness of sunscreens is evaluated in tests that consist of examining the ingredients that compose it individually, and not within the framework of a formulation exposed to sunlight.
“By itself, zinc oxide is an effective and harmless UV blocker, says Richard Blackburn, professor of sustainable materials at Leeds School of Design, who led the study. Our research raises concerns as to how the ingredients in the individual formulation react with each other during use and this is not currently tested by the industry.”
According to research findings, once exposed to sunlight for two hours, zinc oxide destroys the UVA protection provided by the other ingredients. “In this context, putting on sunscreen could actually make it worse because people believe they are protected from harmful UV rays and can stay in the sun longer.”
Up to 90% less efficient
During their tests, the researchers studied how this mineral reacted with the other ingredients when exposed to sunlight and also calculated how much UVA the sunscreen blocked to determine the UVA protection factor of each mixture.
The researchers then found that zinc oxide caused the breakdown of other UV absorbers, which significantly reduced the protection offered by sunscreens, and this in just two hours. The UVA protection factor was thus reduced from 84.3% to 91.8% in the sunscreen mixed with zinc oxide particles, whereas the original sunscreen without zinc oxide showed only a 15.8% loss of UVA protection factor after two hours of UV exposure.
A more toxic formula
Not only did the zinc oxide cause a decrease in the effectiveness of the sunscreen, but it also caused an increase in the toxicity of the formula, say the researchers.
“So not only is the lack of effective UV protection an issue, but the product itself can cause damage while being used in the sun”explains Professor James Hutchison, of the University of Oregon.
Researchers are therefore pleading for new cosmetic formulations of sunscreens that will take into account “the potential for zinc oxide-induced photodegradation throughout the formulation, or when combining products on the skin”.
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