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In 2011, the U.S. Food and Drug Administration said sunscreen labels must emphasize protection against both ultraviolet-A (UV-A), and UV-B radiation. These products would have what's known as "broad spectrum protection" against the sun's dangerous rays.
Both of the UV wavelengths have differing effects on the skin: UV-A is associated with skin aging and UV-B is associated with sunburns, experts note. However, both types are potent risk factors for skin cancer.
But how much of all this is understood by the average sunscreen consumer? In the study, a team led by Dr. Roopal Kundu of Northwestern University Feinberg School of Medicine in Chicago, surveyed 114 patients at a dermatology clinic.
Most -- 93 percent -- said they had bought sunscreen in 2013. When asked why they used sunscreen, 75 percent said to prevent sunburns and about two-thirds said to prevent skin cancer.
However, only 43 percent of the participants understood the definition of SPF value. When it came to labeling, few could correctly identify information that indicated how well the sunscreen protected against skin cancer (38 percent), sunburn (23 percent) or skin aging (7 percent).
"Despite the recent changes in labeling mandated by the U.S. Food and Drug Administration, this survey study suggests that the terminology on sunscreen labels may still be confusing to consumers," Kundu and colleagues wrote.
Skin cancer experts weren't surprised.
"There remains much misunderstanding and even controversy on the amount, number and timing of sunscreen use," said Dr. Doris Day, a dermatologist at Lenox Hill Hospital in New York City.
"Many people, even physicians, still believe sunscreen only needs to be used when they're at the beach," she said. "The reality is that every exposure is harmful to the skin and the exposure is cumulative over time, eventually leading to both skin cancer and skin aging."
So what should a consumer look for in a sunscreen? Dr. Katy Burris is a dermatologist at North Shore-LIJ Health System in Manhasset, N.Y. She said the average person should look for three things on the label:
- An SPF, or "sun protection factor" of at least 30.
- Whether the sunscreen is water- or sweat-resistant. It is important to remember there are no water- or sweat-proof, sunscreens, only resistant ones, Burris said.
- Whether the sunscreen contains physical blockers/screens (such as zinc oxide or titanium dioxide) or a chemical blocker/absorber. "The difference is that chemical blockers absorb the UV radiation, while physical blockers reflect the UV light," Burris said.
She also believes that many people need reminding of what a "SPF," or sun protection factor, means.
"The SPF is an indication of how long it will take you to develop a sunburn as compared to unprotected," Burris said. "So if it normally takes you 10 minutes to burn, an SPF of 30 will allow you to be out for 300 minutes before burning." Most people will need to reapply sunscreen every 2 hours, she added.
And while an SPF of 30 is probably sufficient to protect most people, fair-skinned types or people whose skin is especially sensitive to the sun may want to get something with a higher SPF, Burris said.
About an ounce of sunscreen -- the amount in a shot glass -- should suffice for one application for the average person, she said.
What if you decide to go for a swim? "According to FDA regulations, 'water-resistant' sunscreen means that it maintains its SPF after 40 minutes in the water, while 'very water-resistant' can last up to 80 minutes," Burris said. "Look for those keywords 'water- and/or sweat-resistant,' and remember to allow a few minutes between application and exposure to water so it allows the sunscreen to be absorbed."
The Northwestern University study was published online June 17 in the journal JAMA Dermatology.
-- Robert Preidt
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