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Six ingredients commonly found in sunscreens had systemic absorption levels that exceeded FDA recommendations, according to a clinical evaluation of four sunscreen formulations.

Mean plasma concentrations of avobenzone (primary endpoint) ranged from 3.3 to 7.1 ng/mL across the four sunscreen formulations (one lotion, three sprays). That compared with the FDA recommendation of 0.5 ng/mL.

The other five chemicals evaluated in the study also exceeded the FDA recommendation for each sunscreen that included the chemicals in its overall composition, reported David G. Strauss, MD, PhD, of the FDA Center for Drug Evaluation and Research in Silver Spring, Maryland, and colleagues in .

"All six sunscreen active ingredients tested resulted in exposure above 0.5 ng/mL, and this threshold was reached after one application to 75% of body surface on day 1," the authors stated. "This reinforces the need for additional research to determine the effect of systemic exposure of sunscreen ingredients."

"These findings do not indicate that individuals should refrain from the use of sunscreen," they added.

The study reflects ongoing interest in establishing the safety of chemical-based sunscreens, according to the authors of an .

"Although the safety of mineral sunscreen filters has been established, the safety of chemical sunscreen filters has come under increased scrutiny in light of recent data from investigators at the FDA," wrote Adewole S. Adamson, MD, of Dell Medical School in Austin, Texas, and JAMA Dermatology editor-in-chief Kanade Shinkai, MD, PhD, of the University of California San Francisco.

They referenced a by Strauss and colleagues showing elevated plasma levels of four common sunscreen chemicals measured under maximal-use conditions.

"These were notable findings because systemic safety testing has not been previously documented for these common sunscreen ingredients," Adamson and Shinkai continued.

However, the prior study did not address several key questions about sunscreen safety: systemic absorption after a single use; duration of time plasma concentration exceeding FDA recommendations; evidence of health risks. The current study showed that plasma absorption of all six chemicals exceeded the FDA threshold after a single application and continued to increase with each subsequent application. All the products remained above the threshold on day 7, and two (homosalate and oxybenzone) remained above the threshold on day 21.

Nonetheless, the data reported to date have not addressed the issue of safety.

"In the absence of clear data demonstrating harm, the use of chemical sunscreen may still be considered appropriate," Adamson and Shinkai concluded. "The use of mineral-based sunscreen is a well-established alternative. Elevating the science of the benefits and harms of sunscreen should be a priority. The sunscreen industry must begin conducting these safety studies as recommended by the FDA. Until then, the harms of absorption of sunscreen filters will remain uncertain."

The FDA has regulatory authority over sunscreens, as a type of over-the-counter medication. Early last year, the agency published a that would update regulatory requirements for 16 sunscreen ingredients. The proposal recommended assessment of human systemic absorption of sunscreen ingredients by means of a maximal usage trial.

FDA assessment began with a nonrandomized pilot study, cited by Adamson and Shinkai. The study evaluated systemic absorption of four sunscreen ingredients (avobenzone, oxybenzone, octocrylene, and ecamsule) in four commercially available sunscreen products. All of the tested ingredients were absorbed systemically and remained in plasma for at least 3 days after the last sunscreen application.

In the follow-up study, Strauss and colleagues evaluated systemic absorption of six ingredients (excluding ecamsule and including homosalate, octisalate, and octinoxate) in four sunscreen products (one lotion, one aerosol spray, one nonaerosol spray, and one pump spray). Investigators randomized 48 participants to the four sunscreens.

Conducted within a clinical laboratory, the study protocol specified application of 2 mg/cm² to 75% of body surface once on day 1 and four times (at 2-hour intervals) on days 2 through 4. Each participant contributed 31 blood samples over 21 days. The primary endpoint was the maximum plasma concentration of avobenzone over days 1 through 21.

All but four participants completed the trial. The geometric mean maximum plasma concentration of all six ingredients exceeded 0.5 ng/mL and exceeded the threshold on day 1 for all of the ingredients. The data showed the following mean maximum concentrations by sunscreen type:

• Avobenzone: 7.1 ng/mL (lotion), 3.5 ng/mL (aerosol spray), 3.5 ng/mL (nonaerosol spray), 3.3 ng/mL (pump spray)
• Oxybenzone: 258.1, 180.1, N/A, N/A
• Octocrylene: 7.8, 6.6, 6.6, N/A
• Homosalate: N/A, 23.1, 17.9, 13.9
• Octisalate: N/A, 5.1, 5.8, 4.6
• Octinoxate: N/A, N/A, 7.9, 5.2

No serious drug-related adverse events were reported; 14 participants reported rash.

The authors acknowledged several study limitations, including an indoor setting and no between-group comparisons of plasma concentrations.

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