Applying sunscreen as often as manufacturers recommend results in plasma concentrations of sunscreen’s 4 active ingredients that exceed the threshold for safety concerns established by the US Food and Drug Administration (FDA), according to a recent study. The clinical significance of these findings has not been established, however.
Investigators enrolled in the trial 24 healthy volunteers aged from 18 to 60 years, 14 of whom were black or African American. Participants were divided into 4 groups of 6 individuals, with each group assigned to use 1 of 4 commercially available sunscreens— 2 different sprays, a lotion, or a cream. They applied the products 4 times a day for 4 days, covering body areas generally left uncovered by swimsuits, but not exposed to direct sunlight. Investigators collected multiple blood samples on each of the 4 application days and 3 subsequent days (30 samples for each participant) and assessed them for each of the 4 active ingredients: avobenzone, oxybenzone, octocrylene, and ecamsule.
All 4 products were associated with concentrations greater than 0.5 ng/mL—the FDA’s safety cutoff—that were reached after 4 applications on the first day of the trial. For avobenzone, maximum plasma concentrations for the 2 different sprays, lotion, and cream were 4.0 ng/mL, 3.4 ng/mL, 4.3 ng/mL, and 1.8 ng/mL, respectively. For the 3 products containing oxybenzone (the cream did not include it), plasma concentrations exceeded 20 ng/mL on day 7, and all participants who received formulations containing oybenzone had plasma concentrations exceeding 0.5 ng/mL within 2 hours after a single application on day 1. All 4 products resulted in octocrylene plasma concentrations exceeding 0.5 ng/mL, starting from day 1 and lasting through day 7. Only the cream contained ecamsule, and 5 of 6 participants in the cream group had an ecamsule plasma concentration exceeding 0.5 ng/mL on day 1.
Adverse events, which resolved in all participants, included rash—most common—milia, and pruritis (Matta MK, et al. JAMA. 2019;321:2082-2091).
Thoughts from Dr. Burke
The FDA published this highly publicized report as a preliminary study to determine if sunscreens should be tested for carcinogenicity and embryofetal toxicity. All the active ingredients generated blood levels higher than the threshold the FDA considers below consideration for systemic effect (0.5 ng/mL). However, the authors are quick to note that the clinical relevance of systemic absorption of these compounds is not yet known and suggest that these findings may induce the FDA to ask the manufacturers for further studies. In the meantime, they said, “These results do not indicate that individuals should refrain from the use of sunscreen.” So, as summer continues, recommend sun protection, including liberal use of sunscreen, but keep an eye out for revised recommendations or product changes based on further study.