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The Nuance
The Truth About Mineral vs. Chemical Sunscreens
Exploring the science — and lack thereof — behind sunscreen safety
For a 2019 study, researchers at the U.S. Food and Drug Administration had healthy people apply common, commercially available sunscreens.
For four days — and four times each day — the people in the study sprayed or rubbed sunscreen onto their bodies. Most sunscreen labels advise people to reapply “at least every two hours,” so the study was designed to assess what would happen inside the body if people followed this guidance. For example, if someone went on a beach vacation and slathered on sunscreen throughout the day, as directed, what, if anything, might show up in their blood?
To find out, the study team collected blood samples from each of the participants. They measured the samples for “systemic absorption,” or evidence that the active sunscreen chemicals had leached through the skin and into a person’s blood. Per FDA rules, systemic absorption above 0.5 ng/mL necessitates follow-up research to determine whether a chemical could be cancerous or associated with any developmental or reproductive harms.
The blood samples revealed that all three of the common sunscreen chemicals — avobenzone, oxybenzone, and octocrylene — exceeded the 0.5 ng/mL limit, and all three did so within hours of the first application. But really, “exceeded” is too weak a word. For the people who used a sunscreen containing oxybenzone, blood concentrations swelled to roughly 210 ng/mL, or more than 400 times the safety threshold. The results were less dramatic for the other two chemicals, but all of them easily crossed the limit of scrutiny. Even after people stopped applying the sunscreens, all three of the chemicals continued to circulate in their blood for days.
What all this means for human health is unclear; the study team explained that all of these chemicals lack “safety assessment data.” But prior work — some in people, some in animals or lab settings — has linked these chemicals (particularly oxybenzone) to hormone changes, skin allergies, altered birth weights, and other potential health concerns.
These sorts of findings have led many to ditch these “chemical” sunscreens in…
