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What's true, and what's not, about sunscreen and SPF.

By Ayren Jackson-Cannady

Reviewed by Laura J. Martin, MD

WebMD Magazine - Feature

Sunscreen: Are You Really Covered?

You know you should wear sunscreen every day. But what kind? How long can you keep it?

Get the answers to these questions and other truths about sunscreen.

Sunscreen: True or False

1. The higher the SPF, the better the protection.

FALSE. It sounds right -- a sun protection factor of 100 should be twice as protective as SPF 50. But it's only a few percentage points more effective. An SPF of 15 screens 93% of the sun's rays and an SPF of 30 screens 97%. "But the number becomes irrelevant if you aren't applying enough in the first place," says Mona Gohara, MD, a dermatologist in Danbury, Conn., and an assistant clinical professor at Yale University dermatology department. Most people don't use enough, studies show.

"For better protection apply 1 to 2 ounces (the size of a Ping-Pong ball) of sunscreen on your body 30 minutes before going outdoors [so your skin can absorb it completely] and every two hours to any exposed skin after that," Gohara says.

For your face, apply a dollop the size of a silver dollar every day, no matter what the weather. Note, too, that SPF refers to protection from UVB (the burning rays) only, not UVA (the aging rays). You need to guard against both since both can lead to skin cancer.

2. It's OK to use last year's bottle of SPF.

TRUE. Most sunscreens have a shelf life of about two years, says Jordana Gilman, MD, a New York City dermatologist. If you are using sunscreen properly, however, you shouldn't have any left, since it takes about 1 to 2 ounces of sunscreen to cover the entire body. A 4-ounce bottle should last for, at most, four applications.

3. Sunscreen only needs to be applied to exposed skin.

FALSE. The average T-shirt offers an SPF of about 7, notes Gilman. Darker fabrics and tighter weaves provide more protection, but it is much safer to apply sunscreen to your entire body before you get dressed. Or better yet, wear clothing made of UV protective fabrics. These have been specially treated with colorless UV-absorbing dyes, and most offer an ultraviolet protection factor (UPF) of 50, which blocks both UVA and UVB.

Brush up on Beauty

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