"I chalk it up to some weak years around high school, when I was running and wasn't such a stickler about putting on sunscreen and protecting myself," says Kastor, 34, the fastest woman marathoner in American history. "I'm paying the price right now."
Chances are, many of us haven't been sticklers, either. A recent, widely publicized study found more abnormal moles and lesions in marathoners than nonmarathoners and also reported that only 56 percent of the runners said they put on sunscreen regularly. "The study is not a reason to stop running outdoors," says Peter O'Neill, M.D., a dermatologist in Garden City, New York, who's training for his second marathon. "But it is a reason to start taking sun protection seriously."
Dr. O'Neill recommends using a sunscreen that's waterproof, has an SPF of 30, and offers "broad spectrum" protection, which means it protects against both UVA and UVB rays. "Some sunscreens only protect against B," he says. "But it's the A, the longer wave of ultraviolet light, that penetrates the skin more deeply."
Slather on a good sunscreen at least 20 minutes before you head out so that your skin has time to absorb the lotion. Running early in the morning, before the sun's intensity is at its greatest, is also an important preventive step, as is wearing protective clothing, including a broad-billed hat and sunglasses. "It's nice to run in just a tank top and shorts," says Dr. O'Neill, "but you're better off running like those guys in the desert who wear the long-sleeve, lightweight fabrics."
Which is exactly what Kastor has started doing during her training runs in Mammoth Lakes, California. "The long-sleeve shirts are really thin and light, they have added SPF in the fabric, and they feel fine," she says.
While all the precautions Kastor is now taking haven't been enough yet to overcome either her genetic predisposition or her youthful sun transgressions, she's approaching the situation with a healthy attitude. "That's what this sport is all about," she says. "We run because it's a healthy thing to do."