Sunscreens Containing Zinc Oxide May Lose Effectiveness and Become Toxic After Two Hours: Study

Washington [US], Oct. 15 (ANI): A sunscreen containing zinc oxide, a common ingredient, loses much of its effectiveness and becomes toxic after two hours of exposure to ultraviolet rays, according to a collaboration that included scientists from Oregon State University.

The results were published in the journal ‘Photochemical and Photobiological Sciences’.

The toxicity analysis involved the zebrafish, which shares remarkable similarities with humans at the molecular, genetic, and cellular levels, meaning that many studies on the zebrafish are immediately relevant to humans.

The research team, which included Robyn Tanguay and Lisa Truong, professors at the College of Agricultural Sciences and Claudia Santillan, graduate researcher, sought to answer important but largely overlooked questions regarding the huge global sunscreen market. , predicted by market data company Statista to be worth more than $ 24. billion by the end of the decade.

The questions: How stable, safe and effective the ingredients in sunscreens are in combination rather than as individual compounds – this is how they are considered for approval by the Food and Drug Administration – and what about the safety of any chemicals resulting from reactions caused by exposure “Sunscreens are important consumer products that help reduce UV exposure and therefore skin cancer, but we don’t not know if the use of certain sunscreen formulations can have unintended toxicity due to interactions between certain ingredients and UV light, ”said Tanguay, a distinguished professor at OSU and an international toxicology expert.

What the public thinks about the safety of sunscreens has led manufacturers, often on the basis of limited data, to use a lot of some ingredients while limiting others, she said. For example, oxybenzone has effectively been phased out due to fears that it will harm coral reefs.

“And sunscreens containing inorganic compounds like zinc oxide or titanium dioxide, which block UV rays, are increasingly marketed as safe alternatives to small molecule organic compounds which absorb the rays,” he said. declared Tanguay.

Scientists, including James Hutchinson and Aurora Ginzburg of the University of Oregon and Richard Blackburn of the University of Leeds, have prepared five blends containing UV filters – the active ingredients in sunscreens – from different products available to United States and Europe. They also made additional blends with the same ingredients, plus zinc oxide at the lower end of the commercially recommended amount.

The researchers then exposed the mixtures to ultraviolet rays for two hours and used spectroscopy to check their photostability – that is, what did sunlight do to the compounds in the mixtures and their UV protection capabilities? Scientists also examined whether UV radiation caused any of the mixtures to become toxic to zebrafish, a widely used model organism that goes from egg to swimming in five days, and found that the mixture exposed to UV without zinc oxide caused no significant changes in fish.

“There have been several studies that have shown that sunscreens can react quickly under UV exposure – the setting specifically intended for their use – so it is quite surprising how little toxicity testing has been done on Sunscreen products. photodegradation, ”Truong said. “Our results suggest that the commercially available small molecule formulas, which were the basis of the formulas we studied, can be combined in different ingredient ratios that minimize photodegradation.” But scientists found big differences in photostability and phototoxicity when zinc oxide particles were added – either nanoparticles or larger microparticles.

“Whatever the size of the particle, the zinc oxide degraded the organic mixture and caused a loss of more than 80% of the protection of the organic filter against ultraviolet-A rays, which represent 95% of the UV radiation which reaches Earth, ”Santillan said. noted.

Santillan added, “Additionally, the zinc oxide-induced photodegradation products caused a significant increase in defects in the zebrafish which we used to test for toxicity. This suggests that the zinc oxide particles conduct to degradants whose introduction into aquatic ecosystems is dangerous for the environment. “Tanguay said she was surprised that the five mixtures of small molecules are generally photostable, but not surprised that the addition of particles of Zinc oxide causes toxicity upon UV irradiation.

“As an Oregon State team specializing in studying the toxicity of nanoparticles, these results came as no shock,” she said.

“The results would surprise many consumers who are misled by the ‘nano-free’ labels on mineral-based sunscreens which imply that the sunscreens are safe simply because they do not contain these smaller particles. Any size. of metal oxide particle can have reactive surface sites whether or not it is less than 100 nanometers or not. More important than the size is the identity of the metal, its crystal structure and any surface coating, “a-t -she adds.

The National Science Foundation and the National Institutes of Health supported this research. (ANI)

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