Common chemical filters used in US-approved sunscreens are systemically absorbed into the bloodstream and surpass plasma US Food and Drug Administration (FDA) threshold concentrations for potentially waiving some additional safety studies for sunscreen use, according to study results published in JAMA. Despite these findings, researchers suggested the benefits of regular sunscreen use outweigh potential risks associated with systemic absorption of ultraviolet chemical filters.

In this FDA-funded clinical trial, investigators randomly assigned a total of 48 healthy participants to sunscreens formulated as a lotion (n=12), aerosol spray (n=12), nonaerosol spray (n=12), or pump spray (n=12). Participants applied products at 2 mg/cm2 to 75% of body surface area at baseline on day 1. They then applied sunscreen products 4 times every 2 hours on days 2 through 4. Investigators collected and analyzed blood samples during a 21-day period from each participant, testing the maximum plasma concentrations of avobenzone, oxybenzone, octocrylene, homosalate, octisalate, and octinoxate over days 1 through 21.

Researchers used a systemic exposure threshold of 0.5 ng/mL, as previous research has suggested that the approximated risk for cancer associated with plasma concentrations under this threshold would be <1 in 100,000 after a single-dose exposure.

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The maximum plasma concentrations of avobenzone, the primary outcome of this study, were 7.1 ng/mL (coefficient of variation [CV], 73.9%) for lotion, 3.5 ng/mL (CV, 70.9%) for aerosol spray, 3.5 ng/mL (CV, 73.0%) for nonaerosol spray, and 3.3 ng/mL (CV, 47.8%) for pump. This exceeded the maximum threshold for systemic exposure.

Investigators found similar findings for the other 5 filters. For oxybenzone, the maximum exposure plasma concentrations were as high as 258.1 ng/mL (CV 53%) for lotion and 180.1 ng/mL (CV, 57.3%) for aerosol spray. Octocrylene featured a maximum plasma concentration ranging from 7.8 ng/mL (CV, 87.1%) for lotion to 6.6 ng/mL (CV, 103.9%) for nonaerosol spray. Homosalate had maximum plasma concentrations at 23.1 ng/mL (CV, 68%), 17.9 ng/mL (CV, 61.7%), and 13.9 ng/mL (CV, 70.2%) for aerosol spray, nonaerosol spray, and pump spray, respectively. Octisalate and octinoxate plasma concentrations also greatly exceeded the 0.5 ng/mL threshold for all sunscreen formulations.

In addition, the majority of participants had maximum plasma concentrations that either met or exceeded the 0.5 ng/mL threshold after a single application of each active ingredient. Exposures exceeding the threshold after a single application were found in 83% of participants within 23 hours of avobenzone application, 100% of participants at 2 hours for oxybenzone, 75% of participants at 8 hours for octocrylene, 86% of participants at 3 hours for homosalate, 75% of participants at 6 hours for octisalate, and 75% of participants at 8 hours for octinoxate.

Limitations of this study included the application of sunscreens in an indoor-only environment and the lack of differentiation in absorption among Fitzpatrick skin types.

As the study did not look at the correlation between absorption and disease risk, and considering the association between sunscreen use and a reduction in melanoma risk, the researchers concluded that “these findings do not indicate that individuals should refrain from the use of sunscreen.”

Reference

Matta MK, Florian J, Zusterzeel R, et al. Effect of sunscreen application on plasma concentration of sunscreen active ingredients: a randomized clinical trial. JAMA. 2020;323(3):256-267.