The chemicals that make sunscreen effective have another quality that may not be so great: They leach into the bloodstream quickly, in a matter of hours, according to a new government study in JAMA. FDA researchers emphasize that they want people to continue using sunscreen, but the study hit thresholds that warrant further study, reports Live Science. "Just because they are absorbed doesn’t mean they are unsafe," study coauthor Dr. Theresa Michele tells NBC News. "That’s why we are asking for additional data." The study was small but comprehensive: Twelve men and 12 women applied sunscreen four times a day for four days over 75% of their body—the non-swimsuit areas—and researchers took regular blood samples for a week to monitor four leading chemicals: avobenzone, oxybenzone, ecamsule, and octocrylene.
After the first day of use, all four chemicals exceeded the threshold to trigger additional study—particularly oxybenzone, reports CNN. The results also suggest the chemicals accumulate in the blood as sunscreen is reapplied. However, there's no evidence anything harmful is going on. Relatively little safety testing has been done on the active ingredients to date because they were given the green light decades ago, explains Wired. What's more, they were approved at a time when people generally used sunscreen less than they do today. "[People] should absolutely still use sunscreen," says dermatologist Kanade Shinkai of the University of California, San Francisco, co-author of an accompanying editorial in JAMA. "We definitely know that the sun can cause skin cancer and melanoma." (A writer makes the case that we're overdoing it on sunscreen.)