You’ve probably gotten the message that you should use a sunscreen when you’re out in the sun to protect against skin cancer and skin damage. But the safety of some widely used sunscreen ingredients was called into question after an FDA study, published earlier this year in the Journal of the American Medical Association (JAMA), demonstrated that they are absorbed by the skin and enter the bloodstream. This followed results of a pilot study by the same researchers last year. The studies were small and of short duration, however, and more safety testing is needed to determine if the absorption poses actual health issues. The risk of skin cancer from excessive sun exposure still likely outweighs the risk of any potential harm from the chemicals.
Chemicals of concern
The ingredients in question are those found in so-called chemical sunscreens and include avobenzone, oxybenzone, octocrylene, octisalate, octinoxate, homosalate, and others. Chemical sunscreens are designed to filter the sun’s harmful rays, as opposed to mineral sunscreens containing titanium dioxide or zinc oxide, which form a physical barrier on the skin to block the sun. You can tell the difference between chemical sunscreens and mineral sunscreens when you apply them because the latter typically leave a tell-tale white cast on the skin (though newer formulations have minimized this). Some sunscreens combine zinc oxide with a chemical filter ingredient.
The JAMA study included 48 healthy people who applied one of four commercial chemical sunscreens containing a total of six active ingredients over three-quarters of their bodies for four consecutive days. On the first day, they applied it once; on the rest of the days, they applied it four times at two-hour intervals. Blood was drawn daily for three weeks, starting from the first day of sunscreen application. The sunscreens included one lotion and three different spray formulations—and application was considered “maximal use.”
After just a single application, all six ingredients were detected in participants’ blood, indicating systemic absorption. And the levels were often well in excess of the 0.5 nanograms per milliliter considered by the FDA to be the “Threshold of Toxicological Concern.” Moreover, blood levels exceeded the limit in most participants for 7 to 21 days after the initial application, depending on the ingredient.
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No definitive conclusions
Researchers have raised questions about whether oxybenzone, avobenzone, and other active ingredients in chemical sunscreens disrupt hormones or are carcinogenic. In proposed regulation changes issued last year, the FDA requested manufacturers to submit additional data on 12 chemical sunscreen ingredients to make a final safety determination. As of now, there are no definitive conclusions, and the ingredients are still allowed to be marketed. It’s important to note also that the study participants were in a clinic setting with no direct sunlight, heat, or humidity, which might affect absorption of the ingredients, and the amount of sunscreen applied was more than what is typically used. That is, the study did not test sunscreens under real-life conditions.
The authors of the study concluded that their findings “do not indicate that individuals should refrain from the use of sunscreen.” Still, if you’re concerned, there’s an easy solution: Choose a sunscreen that lists only titanium dioxide or zinc oxide as active ingredients, since these don’t penetrate the skin and are recognized as generally safe and effective by the FDA (and they may be better tolerated if you have sensitive skin). In its Sunscreen Guide, the Environmental Working Group gives these two ingredients a low “hazard score” and cites the most concern about the chemical sunscreen ingredient oxybenzone.
No matter what sunscreen you choose to use, it should be labeled “broad-spectrum” or “UVA/UVB protection” with an SPF of 30 or higher. Apply it at least 15 minutes before you go in the sun to give it enough time to dry and form an even film on the skin. Reapply all sunscreen at least every two hours and after swimming. It’s also essential to take other sun safety steps to protect your skin, including wearing a hat, sunglasses, and protective clothing (see inset) and limiting time outside during peak sun hours.
This article first appeared in the UC Berkeley Wellness Letter.
Also see Are ‘Sunscreen Pills’ for Real?
Published August 18, 2020