Sunscreen that contains zinc oxide, a common ingredient, loses its effectiveness and becomes toxic after two hours of exposure to ultraviolet radiation, according to a collaboration of scientists at Oregon State University. The findings were published in the journal ‘Photochemical and Photobiological Sciences’. The toxicity analysis included zebrafish, which share a remarkable similarity to humans at the molecular, genetic and cellular levels, meaning that many zebrafish studies are immediately relevant to people. The research team, which included Faculty Robin Tangue and Lisa Truong of the College of Agricultural Sciences and Graduate Fellow Claudia Santillon, sought to answer important but largely neglected questions about the global sunscreen market at large, which is predicted by the market. Data firm Statista had predicted more than USD 24. billions by the end of the decade
Q:How stable, safe, and effective are sunscreen ingredients in combination rather than as individual compounds — that’s how they are considered for Food and Drug Administration approval — and what about the safety of any chemical products that result from reactions? Exposure to sunlight?
“Sunscreens are important consumer products that help reduce UV exposure and thus skin cancer, but we do not know whether the use of some sunscreen formulations may result in unintended toxicity due to interactions between certain ingredients and UV light,” Said Tangue, an OSU Distinguished Professor and an international expert in toxicology.
That’s what the public thinks about sunscreen safety, which is why manufacturers, often based on limited data, use too many ingredients while limiting others, she said. For example, oxybenzone has been effectively discontinued due to concerns that it harms coral reefs.
“And sunscreens containing inorganic compounds such as zinc oxide or titanium dioxide, which block UV rays, are being marketed more and more heavily as safer alternatives to organic small-molecule compounds that absorb rays,” Tangue said.
Scientists including James Hutchinson and Aurora Ginzburg of the University of Oregon and Richard Blackburn of the University of Leeds created five blends containing UV filters from a variety of products available in the United States and Europe – the active ingredients in sunscreens. They also made additional mixtures with similar ingredients, plus zinc oxide, at the lower end of the commercially recommended amount.
The researchers then exposed the mixture to ultraviolet radiation for two hours and used spectroscopy to investigate their photostability – that is, what did sunlight do to the compounds in the mixture and their UV-protective abilities? The scientists also looked at whether UV radiation had made any of the mixtures toxic to zebrafish, a widely used model organism that takes five days to swim from an egg, and found that zinc oxide was present in the body. The un-UV-exposed mixture did not cause any significant changes in the fish.
“There have been several studies that show that sunscreens can react quickly under UV exposure — especially the setting intended for their use — so it’s surprising how little toxicity testing has been done on photodegradation products,” Truong said. said. “Our findings suggest that commercially available small-molecule-based formulas, which were the basis for the formulas we studied, can be combined in different component ratios that reduce photodegradation.”
But the scientists saw big differences in photostability and phototoxicity when zinc oxide particles were added – either nanoparticles or larger microparticles.
“With any size of particle, zinc oxide degrades the organic mixture and caused more than 80 percent loss in organic filter protection against ultraviolet-A rays, which make up 95 percent of the UV radiation reaching Earth,” Sentillon said.
“In addition, zinc-oxide-induced photodegradation products caused a significant increase in the defects of the zebrafish that we used to test toxicity. This suggests that zinc oxide particles tend to degrade which Introducing aquatic ecosystems is environmentally dangerous.”
Tangue said she was surprised that all five small-molecule mixtures were generally photostable but not surprised that the addition of zinc oxide particles caused toxicity upon UV irradiation.
“As a team at Oregon State that specializes in studying nanoparticle toxicity, these results were not a shock,” she said.
“The findings will surprise many consumers who are misled by the ‘nano-free’ label on mineral-based sunscreens, which means that sunscreens are safe because they do not contain those tiny 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 identity of the metal, its crystal structure and any surface coatings.”
The National Science Foundation and the National Institutes of Health supported this research.
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