Your sunscreen isn’t protecting you as much as you think


WITH summer in full swing, many people are dutifully applying their sunscreen before heading outside. But your sunscreen may not be protecting you as much as you think, a new study suggests. This isn’t due to any fault of the product, though, but rather to the way people apply sunscreen — consumers tend not to apply sunscreen in a thick enough layer to get the full benefits, the researchers say.
The study, published July 24 in the journal Acta Dermato-Venereology, found that, when sunscreen with a sun-protection factor (SPF) of 50 is applied in a “typical” way (that is, in a relatively thin layer), it provides at best only 40 percent of the expected protection.
“There is no dispute that sunscreen provides important protection against the cancer-causing impact of the sun’s ultraviolet rays,” lead study author Antony Young, a professor at St. John’s Institute of Dermatology at King’s College London in the United Kingdom, said in a statement. “However, what this research shows is that the way sunscreen is applied plays an important role in determining how effective it is,” Young said.
It’s known that applying too little sunscreen can result in sunburns and skin damage. But the new study is one of the first to assess how much DNA damage occurs in the skin when people apply sunscreen in a “typical” way — that is, when they apply less than the amount used when manufacturers test sunscreens to determine their SPF rat-ing. That amount, according to the study, is 2 milligrams per centimeter squared (mg/cm^2).
The study involved 16 people with fair skin who were exposed to ultraviolet radiation (UVR) to simulate sunlight. (Just a small part of the participants’ skin was exposed.) Sunscreen was applied to participants’ skin at various thicknesses, ranging from 0.75 mg/cm^2 (considered “typical” use), up to the recommended 2 mg/cm^2. Some participants were exposed to the UVR for five consecutive days, to mimic typical vacation conditions. The researchers also varied the dose of UVR exposure, ranging from low to high intensity.
At the end of the experiment, the researchers took biopsies of the skin that was exposed to the UVR. The biop-sies showed that, after repeated UVR exposure, there was considerable DNA damage on areas that received no sun protection, even though the dose of UVR used on these areas was very low. (For ethical reasons, the dose of radia-tion used on unprotected skin was a minimal dose that would not induce sunburn.)
In fact, just one day’s worth of low-dose UVR exposure to an area without sunscreen resulted in more DNA damage than five days’ worth of high-dose UVR exposure to an area with sunscreen applied at recommended thickness, the researchers said.

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