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Understanding Sun Protection

Protect yourself from harmful rays by understanding the science behind your sun-shielding gear and products.

Heading out the door? Read this article on the new Outside+ app available now on iOS devices for members! Download the app.

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To get all the pertinent facts regarding the rays game, we turned to Leslie Chow, president of the sun-blocking clothing company Iconic. A multi-sport athlete and former NASA researcher, she’s a pro when it comes to the science behind protection.

“UV radiation is a proven carcinogen,” Chow says. “One blistering sunburn in childhood or adolescence or five sunburns at any age doubles your risk of melanoma.” She adds that effects are cumulative and “90 percent of visible sun aging (wrinkles, pigment changes, etc.) are from UV exposure.”

Chow explains that more than 20 percent of Americans will suffer from skin cancer during their lives and the more active you are outdoors (especially if you live in the sunbelt), the greater your risk.

“Sun Protection Factor” measures the time it takes for skin to redden, so the higher the number, the longer you’re covered. The Skin Cancer Foundation explains: “If it takes 20 minutes for your unprotected skin to start turning red, using an SPF 15 sunscreen theoretically prevents reddening 15 times longer—about five hours.” Dr. Steven Wang of Memorial Sloan-Kettering Cancer Center in New Jersey says, “For patients who really wish to know ‘how high should I go?’ I suggest products with SPFs no lower than 30 and no higher than 50.”

Protection levels in clothing may drop by 50 percent when garments made from natural fibers, such as cotton and linen, get wet—but more and more sun-protective clothing is coming out. You can also wash UPF into your regular clothing with a product, such as SunGuard ($4,, which will last through 20 future washings.

“Ultraviolet Protection Factor” represents the amount of the sun’s harmful UV rays that passes through a fabric. A rating of 25 indicates that 1/25th or 4 percent of the UV rays pass through the garment. The Skin Cancer Foundation offers this advice: A UPF rating of 30 to 49 offers “very good protection” and 50-plus is “excellent.”

Cancer concerns come from the sun’s ultraviolet (UV) radiation, which comes in long-wave UVA and shortwave UVB rays. It’s the UVB rays that cause sunburns, but if your sunscreen only filters those out, the UVA rays can still damage your skin without your knowing. Sunscreens labeled with “broad spectrum” protect against both rays.


1. Schedule high-sun exposure activities before 10 a.m. or after 4 p.m.
2. Sport sun-protective apparel, including sunglasses and hats.
3. Wear sunscreen, and reapply every few hours if you’re sweating or swimming.