The Truth About Spf

With an ever-growing array of sunscreen products, it's easy to get confused about what to buy. Some basics: SPF (sun protection factor) ratings apply to a band of ultraviolet light called UVB, the key culprit in skin cancer. SPF 15 (the lowest number recommended by doctors) blocks all but 1/15, or about 93 percent, of UVB. (SPF 2 blocks just 50 percent; SPF 30, about 97 percent.) Don't assume that SPF 60 will protect you twice as long as 30. Unlike the vast variation between SPF 5 and 15, the difference between 30 and numbers above is so minimal that the FDA may eliminate the higher ratings and call the entire category "30-plus."

Another band of light called UVA seems to play a role in skin cancer, too. So many products promise "broad spectrum" protection. But with no UVA ratings (at least for now--they may soon be required), there's no way to tell what you're getting. You can, however, look for specific ingredients that block UVA, like zinc oxide, avobenzone and titanium dioxide. And if you go to Europe or Canada, try creams containing mexoryl--some researchers consider it the best UVA protection, but it's not yet available in the United States.

Here's what's important: how much sunscreen you put on is as crucial as its SPF. Be generous--use at least one ounce (about a shot-glass full) every time. If your bottle says "waterproof," don't assume you can safely dunk in and out of the pool all day. Products have to pass only an 80-minute waterproof test, so you need to reapply every two hours for full protection.

Finally, never rely on creams alone. "I use sunscreen as a third line of defense," says Dr. Arthur Sober of the American Academy of Dermatology. The first two: stay out of the midday sun--and cover up.