"Evidence is mounting that occasional sun exposure increases the risk of melanoma far more than the kind of daily dose a farmer or construction worker might get," says Marianne Berwick, Ph.D., professor of epidemiology at the University of New Mexico. One theory is that skin can't adapt fast enough—that is, after being exposed only to weak winter rays, skin has no mechanisms to protect itself against a sudden blast of UV radiation. Even a moderate vacation tan may be harmful, Berwick says.
What You Should Do: Enjoy the sun safely. When going somewhere sunny, pack sunscreen with an SPF of at least 15, a broad-brimmed hat, and lightweight long-sleeved shirts, long pants or long skirts that have either been laundered in an additive that washes in sun protection (such as Rit SunGuard) or are from a company that makes sun-protective clothing (such as items sold at sunprecautions.com or coolibar.com). One thing you shouldn't do: Prep your skin for vacation by getting a "base tan" at a tanning salon. "The mix of artificial ultraviolet light you get in a tanning booth won't protect your skin from exposure to real sunlight, but it will damage your skin and increase your risk of melanoma," says Berwick.