When used as directed, are sunscreen ingredients absorbed? The FDA waives toxicity testing on sunscreens if the steady state concentration of active ingredients is less than 0.5 ng/mL.
A small study in 24 healthy participants measured serum concentrations of common sunscreen ingredients – avobenzone, oxybenzone, octocrylene and ecamsule. Participants used 1 of 4 different sunscreen products (2 sprays, 1 lotion and 1 cream). The sunscreens were applied 4 times daily for 4 days over 75% of the body, representing skin exposure outside normal swimwear. Blood samples were collected over 7 days. The serum concentration of all active ingredients was at least 0.5 ng/ mL on the first day (the threshold at which products should undergo safety testing) and levels of 3 ingredients continued to rise, suggesting accumulation. The concentration of ecamsule, in a cream formulation, could not be calculated due to limited data.
The authors called for further testing to sort out the clinical significance of these results. It isn’t clear that absorption is harmful, while prolonged sun exposure is known to be harmful. Until more is known, tell patients to continue using sunscreen for UV protection.
• Matta MK, et. al. JAMA 2109.