Sunscreen is a must, even in winter. Burning UVB rays are less of an issue this time of year than UVAs, the aging kind that also cause skin cancer, says Heidi Waldorf, MD, director of laser and cosmetic dermatology at Mount Sinai Medical Center in New York City. That means you can get by with a lower daily SPF level — a 15 rather than a 30 — as long as the formula properly shields against UVA radiation. "Check ingredients lists for avobenzone, mexoryl, titanium dioxide, or zinc," Dr. Waldorf says. But if you enjoy winter sports, stick with SPF 30. "Snow reflects 40 percent of the sun's rays onto your skin, and altitude magnifies this effect," she says.