Kyungho Choi, a professor of environmental toxicology at Seoul National University, argues that sunscreen ingredients have not been studied rigorously enough and points to research showing that some compounds can be absorbed into the bloodstream, detected in urine, and may hurt kidney and liver function.
“Sunscreen is just like a nicotine patch. Those ingredients keep constantly absorbing into your skin for a long time,” Choi says. “We do not have enough information to be sure these compounds are safe to be used.”
Still, many dermatologists argue that the proven benefits of sunscreen outweigh the potential risks.
“Definitely, [when sunscreen] gets absorbed, it can be detected in blood—for weeks, in some cases—but the clinical significance is not known,” says Lim. Some studies suggesting harm were conducted in animals or involved direct ingestion rather than absorption through the skin, he says.
Those regulatory differences have also shaped what kinds of sunscreens companies can make. In recent years, researchers in Korea and Europe have figured out how to capitalize on new-age UV filters to combine UV protection with other skincare benefits, but many of those beneficial compounds “don’t play well with the existing filters in the U.S.,” Li says.