SPF isn't like some weird percentage value of how much solar radiation the stuff blocks, it's a multiplier telling how long the sunscreen extends your burn free sun time. "If your skin takes five minutes to burn and you put on SPF 30, now you have 150 minutes," says Wang.
He says that while the rat studies are compelling, they don't tell the whole story. "What people need to understand is the toxicology," he says. "You need to figure out the exposure level to know how much of a hazard these really are. " Wang's research showed that a human would need to be applying sunscreen every day for decades to accumulate toxic levels of oxybenzone.
Remember what it looks and feels like. "You need two milligrams of sunscreen per square centimeter of skin," says Wang, so about an ounce and a half should be enough to cover your arms, legs, torso, and face.
Organic sunscreen chemicals take advantage of the first law of thermodynamics. "Energy has to go somewhere," says Wang.
Unless you wear sunscreen. "It's solving a physics problem, because that energy has to go somewhere," says Wang.
How does sunscreen prevent you from getting burnt? https://t.co/fDl7k8CVtZ— WIRED (@WIRED) July 5, 2019
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