You may want to think twice before spending a few extra dollars on that zinc oxide sunscreen. The previously deemed “safe” ingredient grabbed our attention over the summer after the recall of several other sunscreen brands that contained carcinogens. Experts recommended replacing these brands with those containing zinc oxide for a cleaner and safer option. However, new evidence stemming from an Oregon State University study suggests an alarming contradiction.
According to findings published October 13 in OSU Photochemical and Photobiological Sciences, zinc oxide is not only less effective than thought, but actually becomes toxic after just two hours of ultraviolet ray exposure. The findings were a result of studying zebrafish, a species scientists say share significant similarities with humans.
Researchers included Robyn Tanguay and Lisa Truong, OSU College of Agricultural Sciences faculty members, and Claudia Santillan, OSU graduate fellow. Together, their goal was to discover truths within the $24 billion sunscreen industry, including the safety and efficacy of sunscreen ingredients — particularly, ingredients that cause reactions after sunlight exposure.
“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 Tanguay. In addition to her contributions at the College of Agricultural Sciences, Tanguay is also a toxicology expert. She added that public views have influenced sunscreen manufacturing, which has been based on limited scientific evidence. An example of this would be the cancellation of oxybenzone as an ingredient due to environmental concerns involving coral reef damage.
“And 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,” said Tanguay.
The research team concocted mixtures made with common sunscreen ingredients, then created replicas of those mixtures and added zinc oxide. The mixtures were then exposed to ultraviolet rays for two hours, and scientists watched the compounds’ reactions, as well as toxicity levels when exposed to zebrafish. Their findings showed that the non-zinc-oxide mixtures did not show toxic reactions in the fish.
“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,” said Truong. “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.”
Their findings, however, did show significant reactions with the mixtures containing zinc oxide.
“With either size of particle, zinc oxide degraded the organic mixture and caused a greater than 80% loss in organic filter protection against ultraviolet-A rays, which make up 95% of the UV radiation that reaches the Earth,” Santillan explained. “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.”
Tanguay added that she was not surprised at the findings regarding zinc oxide.
“As a team at Oregon State that specializes in studying nanoparticle toxicity, these results were not a shock,” she said. “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.”
By: Rebekah Harcrow
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