While sunscreen protects the skin from the sun, a common chemical used to make it may become dangerous when exposed to chlorinated water and ultraviolet radiation.

Scientists from the Faculty of Chemistry of the Lomonosov Moscow State University investigated the nature of chemical compounds formed as a result of the breakdown of avobenzone—found in many sunscreen products as well as in lipsticks, creams and other cosmetics.

Avobenzone is a derivative of the chemical compound dibenzoylmethane and is considered the most popular UV filter in the world because it absorbs ultraviolet light in a wide range of wave lengths.

While avobenzone itself is considered safe, the researchers discovered that in water solution and under ultraviolet radiation it’s capable of breaking down into hazardous chemical compounds.

The researchers simulated situations where swimmers would apply sunscreen to see how the breakdown of avobenzone may take place on wet human skin.

They found that the chemical forms various organic compounds belonging to the classes of aromatic acids and aldehydes, phenols and acetyl benzenes when it breaks down in water. Phenols and chlorinated acetyl benzenes are considered to be extremely toxic.

“On the basis of the experiments one could make a conclusion that a generally safe compound transforms in the water and forms more dangerous products,” Albert Lebedev, Ph.D., one of the project authors, said in a statement. “In spite of the fact that there are no precise toxicological profiles for the most established products, it's known that acetyl benzenes and phenols, especially chlorinated ones, are quite toxic.”

The researchers used a research method called chromatomass spectrometry, which allows conducting qualitative and quantitative analysis of the most complex mixtures of chemical compounds.

“Studying the products of transformation of any popular cosmetics is very important as very often they turn out to be much more toxic and dangerous than their predecessors,” Lebedev said. “In principle, basing on such researches, one could obtain results, which could restrict or even put under a ban the usage of one or another product and preserve health of millions of people.”

The researchers are now studying how avobenzone breaks down under conditions of chlorination and bromination of freshwater and sea water.

The study was published in Chemosphere.