We’ve already seen scientists research the effects of urine and pharmaceuticals in pool water. Now they’re scrutinizing a poolside staple.

The U.S. Environmental Protection Agency is studying how an ingredient in sunscreen reacts when exposed to chemicals in swimming pool water.

This is just a small part of a much larger study examining the environmental impacts of engineered nanomaterials, which are used in a wide variety of consumer products. In this case, scientists are zeroing in on titanium dioxide (TiO2) — the thing that protects skin from harmful UV rays.

Here’s the thing about titanium dioxide: In the presence of water and UV radiation, it decomposes into other molecules, including a reactive oxygen species that has been shown to cause tissue damage. To prevent this, sunscreen manufacturers wisely place a protective coating around the material, called aluminum hydroxide.

EPA researchers wanted to learn how the protective layer holds up against the rigors of a chemically treated pool.

“It was an exploratory study to see — proof of concept — whether or not this material became more toxic after the coating was degraded,” said Dr. William Boyes, a toxicologist who is helping lead the EPA’s emerging materials research.

Sure enough, results from the study show that, after three days in simulated pool water, the protective layer began to degrade, increasing potential toxicity.

While lab tests indicate that there is potential for cell damage resulting from the leaked toxins, swearing off SPF would be unwise.

“At this point, it would be a great leap to assume that there’s a health risk to swimmers,” Boyes says. “If there is a potential risk, it’s most likely going to be associated with aquatic organisms in a lakeside, or something like that.”

In other words, keep slathering.