Researchers from the FDA conducted a small randomized clinical trial of 24 healthy volunteers to determine bloodstream concentrations of four active ingredients (avobenzone, oxybenzone, octocrylene and ecamsule) in four sunscreens applied four times per day for four days with blood samples collected from study participants over seven days.
Researchers report that all four active ingredients were found in blood samples at levels exceeding the threshold recommended for toxicology testing. The effect of these concentrations is unknown and further studies are needed to determine the clinical significance of these findings.
Some limitations of this clinical trial include that it was conducted under indoor conditions without exposure to heat, sunlight or humidity, which may affect the rate of sunscreen absorption, and the study wasn't designed to look at differences in absorption by the type of sunscreen formulation, skin type or age of the user.
Researchers emphasize that their results don't suggest people refrain from using sunscreen, which prevents skin damage.