Science & Technology

Sunscreens containing zinc oxide are ineffective and become toxic after 2 hours

Sunscreens containing the common ingredient zinc oxide lose much of their effectiveness and become toxic when exposed to UV light for two hours, according to a collaborative study involving scientists at Oregon State University.

Toxicity analysis includes zebrafish, which share significant human similarities at the molecular, genetic, and cellular levels. That is, many zebrafish studies are immediately relevant to people.

The survey results were released today (October 13, 2021) Photochemistry and photobiological science.

A research team, including Robyn Tanguay and Lisa Truong of the Faculty of Agriculture, and alumni Claudia Santillan, sought to answer important but largely ignored questions about the huge global sunscreen market predicted by market data firm Statista. $ 24 billion By the end of 10 years.

Question: How stable, safe and effective are sunscreen ingredients in combination, not as individual compounds? This is a method considered for Food and Drug Administration approval-and what about the safety of chemical products resulting from the reactions caused by exposure? In Nikko?

“Sunscreens are an important consumer product that helps reduce exposure to UV rays and reduce skin cancer, but due to the interaction of some ingredients with UV rays, the use of some sunscreen formulations. I don’t know if it can cause unintended toxicity, “said OSU celebrity Tangai. Professor and international expert in toxicology.

The general public’s belief in sunscreen safety has led manufacturers to use more ingredients, often limiting other ingredients based on limited data. .. For example, oxybenzone has been virtually discontinued due to concerns about harm to coral reefs.

“And sunscreens containing UV-blocking inorganic compounds like zinc oxide and titanium dioxide are increasingly being sold as safe alternatives to light-absorbing small molecule organic compounds,” Tangai said. rice field.

Scientists, including James Hutchinson and Aurora Ginzburg at the University of Oregon and Richard Blackburn at the University of Leeds, have created five mixtures from a variety of products available in the United States and Europe, including UV filters, the active ingredient in sunscreens. They also made an additional mixture of the same ingredients plus zinc oxide at the lower limit of the commercially recommended amount.

The researchers then exposed the mixture to UV light for 2 hours and used spectroscopy to check the light stability. So how did sunlight affect the compounds in the mixture and their UV protection?

Scientists also investigated whether UV light caused any of the mixture to become toxic to zebrafish, a widely used model organism that transitions from eggs to swimming in five days, and is zinc oxide-free. An important change in fish that we found was not due to a mixture exposed to UV light.

“There are several studies showing that sunscreens react rapidly under UV irradiation-settings specifically intended for their use-thus, most toxicity tests are performed on photodegradation products. It’s pretty amazing that it’s not being broken, “Truong said. “Our findings suggest that the off-the-shelf small molecule-based formulations that underlie the formulations we studied can be combined in different component ratios that minimize photolysis. “

However, scientists have seen significant differences in photostability and phototoxicity with the addition of zinc oxide particles (nanoparticles or larger particles).

“In both sizes of particles, zinc oxide breaks down the organic mixture and loses more than 80% of the protection of the organic filter against UV A, which accounts for 95% of the UV light reaching the Earth,” said Santilarn. .. “Also, zinc oxide-induced photodegradation products significantly increased the defects of the zebrafish used to test toxicity, which is due to the introduction of zinc oxide particles into aquatic ecosystems. It suggests that it leads to harmful decomposition products. “

Tangai said he was surprised that all five small molecule mixtures were generally photostable, but was not surprised that the addition of zinc oxide particles caused toxicity during UV irradiation.

“As a team at Oregon State University specializing in nanoparticle toxicity research, these results weren’t a shock,” she said. “The findings will surprise many consumers who are confused by the” nano-free “label of mineral-based sunscreens. Metal oxide particles of any size, whether less than 100 nanometers, can have reactive surface sites. More important than size is the identity of the metal, its crystal structure, and its surface coating. “

Reference: “Zinc Oxide Changes in Sunscreen Ingredient Effectiveness and Toxicity under UV Irradiation” October 13, 2021 Photochemistry and photobiological science..

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

Sunscreens containing zinc oxide are ineffective and become toxic after 2 hours Sunscreens containing zinc oxide are ineffective and become toxic after 2 hours

Back to top button