During use, some sunscreens offer very limited protection from dangerous sunlight and can even be harmful.
Chemical reactions involving a major ingredient, zinc oxide, make many sunscreens ineffective after just two hours of sun exposure, according to a new collaborative study between the University of Leeds and the University of Leeds. Oregon and Oregon State University.
Researchers are now calling for new innovative ingredients to be considered for use as ultraviolet (UV) filters to help provide effective protection.
Richard Blackburn, a professor of sustainable materials at the Leeds School of Design, led the study part of Leeds and worked with the two U.S. academic teams in Oregon.
He said current testing practices need to be changed, which include examining the ingredients individually instead of being part of a formulation exposed to sunlight.
By itself, zinc oxide is an effective and harmless UV blocker. Our research raises concerns about how the ingredients of the individual formulation react with each other during use and this is not currently tested by industry.. “
Richard Blackburn, Professor of Sustainable Materials at the University of Leeds School of Design
“Once exposed to sunlight for two hours, zinc oxide destroys the UVA protection provided by other ingredients. In this context, wearing sunscreen could make things worse because people believe it is protected from harmful UV rays. and can stay in the sun longer. “
There are two main types of ultraviolet light: UVA and UVB, both forms of electromagnetic radiation that can cause skin cancer.
UVB is most commonly associated with short-term direct effects, such as sunburn, while UVAs can cause more long-term DNA damage, such as wrinkles and skin aging.
Sunscreens use a 5-star UVA rating, which demonstrates the protection the lotion provides against harmful ultraviolet rays.
Many sunscreens include zinc oxide, which has been shown to help block UV rays. During their tests, the researchers examined how the mineral reacted to other ingredients when exposed to sunlight and also calculated how many UVAs the sunscreen blocked to determine the UVA protection factor of each mixture.
Professor James Hutchison and fellow University of Oregon Aurora Ginzburg co-led the study.
“During testing, we found that zinc oxide causes degradation of other UV absorbers, and the protection provided by sunscreens was significantly reduced in a relatively short time, especially in the UVA region,” he said. Professor Hutchison, Lokey-Harrington Chair of Chemistry and Senior Associate Vice President on the Phil and Penny Knight campus of the University of Oregon for accelerating scientific impact.
The Oregon and Leeds teams found that the UVA protection factor was reduced by 84.3% to 91.8% in sunscreen mixed with zinc oxide particles, while the original sunscreen without zinc oxide only showed a 15.8% loss in UVA protection factor, after exposure to UV. for two hours.
“The degradation of UV filters not only decreased the effectiveness of the sunscreen, but also caused greater toxicity of the formulas,” Professor Hutchison said.
“Therefore, the lack of effective UV protection is a problem, but the product can cause damage during use in the sun.”
Zinc oxide is classified as a mineral and is widely used by brands as a “chemical-free” ingredient (despite being a chemical) in a wide range of cosmetics that are promoted as “natural” ingredients. more gentle on the skin.
But this study questions those claims and requires that they be considered alternatives, Dr. Ginzburg said.
“Zinc oxide particles are often combined with UV filters in hybrid sunscreens or through layers of multiple cosmetics,” he explained.
“Therefore, in the design of future cosmetic formulations, it is critical to consider the potential of zinc oxide – induced photodegradation of the entire formulation or in the combination of products on the skin.
“Loss of UVA protection is especially problematic in U.S. sunscreens where the list of approved filters is so small.”
The study is a call to action for the development of new sunscreen ingredients, Professor Blackburn said.
“Alternatively, there are some excellent potential candidates in nature that are effective UV filters, but under current legislation the process to get regulatory approval is extremely costly and takes many years.
“This is proving to be a barrier to innovation, which could provide more effective, safe and sustainable alternatives to current ingredients.”
Ginzburg, AL, et al. (2021) Zinc oxide-induced changes in the efficacy and toxicity of sunscreen ingredients under UV irradiation. Photochemical and photobiological sciences. doi.org/10.1007/s43630-021-00101-2.