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Evaluation: Measuring Up the UV Index
By Ami Walsh

If you pay any attention to your local TV or radio meteorologist, you’ve probably noticed the National Weather Service’s UV Index in the daily forecast. This number is an attempt to rate, for a given day and location, how much of the sun’s ultraviolet radiation will be sneaking through the ozone layer and into you–and upping your chances of developing skin and eye ailments
from sunburn to cataracts to cancer. The National Oceanic and Atmospheric Administration analyzes satellite data and then rates solar exposure on a scale from zero (it’s probably raining) to 15 (not far from the equator at high noon).

So how do you use the index to prepare for an outing? You don’t. “Whether the index says it’s a three day or a 12 day,” says Dr. Darrell Rigel, a dermatologist at New York University Medical School, “your sunscreen should have a sun protection factor of 15 or above.” In other words, even if you can’t see your shadow, apply SPF 15 sunscreen liberally, and wear sunglasses that
are certified to block 99 to 100 percent of ultraviolet light. The lenses of your sunglasses, by the way, should be bigger than a silver dollar; those fashionably tiny ones offer unfashionably tiny protection. And it’s true what you’ve heard about clouds being no buffer–they only make UV matters worse. “Scattered clouds reflect radiation and up your dosage just like a day on the
water does,” explains Drusilla Hufford, a branch chief in the EPA’s Stratospheric Protection Division. “If it’s not completely overcast and raining, you’re being exposed.”