Sunscreens have become an integral component of our daily skincare routine for years. It shields the skin from sunburn and sun damage. Skincare experts frequently advise against going outside without sunscreen.
According to a new study, sunscreens containing zinc oxide can lose their effectiveness and become harmful after two hours of ultraviolet (UV) radiation. The findings were published in the journal ‘Photochemical and Photobiological Sciences’.
The toxicity analysis involved zebrafish, which shares a remarkable similarity to humans at the molecular, genetic, and cellular levels, meaning many zebrafish studies are immediately relevant to people.
According to the report
The research team, which included College of Agriculture Sciences faculty Ms. Robyn Tanguay and Ms. Lisa Truong and graduate fellow Ms. Claudia Santillan, sought to answer important but largely unanswered questions about the massive global sunscreen market, predicted by market data firm Statista to be worth more than $24 billion by the end of the decade.
“Sunscreens are important consumer products that help to reduce UV exposures and thus skin cancer, but we do not know if the use of some sunscreen formulations may have unintended toxicity because of interactions between some ingredients and UV light,” said Ms. Tanguay, an OSU distinguished professor and an international expert in toxicology.
“Sunscreens containing inorganic compounds like zinc oxide or titanium dioxide, that block UV rays, are being marketed more and more heavily as safe alternatives to the organic small-molecule compounds that absorb the rays. There have been several studies that showed sunscreens can quickly react under UV exposure — the specifically intended setting for their use — so it’s pretty surprising how little toxicity testing has been done on the photodegradation products. Our findings suggest that commercially available small-molecule-based formulas, which were the basis for the formulas we studied, can be combined in different ingredient ratios that minimize photodegradation.”
Scientists including the University of Oregon’s James Hutchinson and Aurora Ginzburg and the University of Leeds’ Richard Blackburn developed five mixtures comprising the UV filters, the active ingredients in sunscreens from different products available in the US and Europe. They also created more mixes with the same components and a lower amount of zinc oxide than the commercially suggested level.
The mixes were then subjected to ultraviolet radiation for two hours, and their photostability was tested using spectroscopy. The researchers then examined to see if UV light made any of the mixes hazardous to zebrafish, a popular model organism that can progress from egg to swimming in five days. They discovered that the UV-exposed mixture without zinc oxide did not affect the fish.
When zinc oxide particles, either nanoparticles or bigger microparticles, were introduced, however, scientists noticed significant variations in photostability and phototoxicity. Ms. Santillan remarked, “With either size of the particle, zinc oxide degraded the organic mixture and caused a greater than 80 percent loss in organic filter protection against ultraviolet-A rays, which make up 95 percent of the UV radiation that reaches the Earth.”
She further added, “Also, the zinc-oxide-induced photodegradation products caused significant increases in defects to the zebrafish we used to test toxicity. That suggests zinc oxide particles are leading to degradants whose introduction to aquatic ecosystems is environmentally hazardous.”
“The findings would surprise many consumers who are misled by ‘nano free’ labels on mineral-based sunscreens that imply the sunscreens are safe just because they don’t contain those smaller particles. Any size of metal oxide particle can have reactive surface sites, whether it is less than 100 nanometers or not. More important than size is the metal identity, its crystal structure, and any surface coatings,” concluded Ms. Santillan.
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