Let’s start with the bad news: The sunscreen you’re used to relying on for beach days probably isn’t going to cut it in the mountains.

For starters, there’s the sheer intensity of the sun at altitude. For every 1,000 feet you gain in elevation above sea level, the intensity of the sun’s rays increase by up to 10 percent. So if you’re skiing in Breckenridge, Colorado at 10,000 feet, you’re dealing with UV radiation that’s up to 100 percent stronger than sun at sea level—so twice as intense. Add the effects of snow reflection, and that percentage jumps even higher.

“High altitude is where you’ll find the absolute most intense challenge to your skin, far more than surfing on the equator at noon,” says Steve Johnson, founder and general manager of Sol Sunguard. Adding insult to injury, “Most sunscreen is tested at sea-level,” he says. “That’s at a 100-percent UV standard, not additional intensity you’re getting on a sunny day at 10,000 feet.”

Bernie Rosow applying sunscreen. (Photo: Christian Pondella)

So if you’re getting burned on the mountain despite wearing sunblock, it might not be because you forgot to reapply. Instead, it could be because your sunscreen chemicals disintegrated under a blast of UV rays way stronger than they were ever intended to withstand.

This is the issue with chemical sunscreens, Johnson says. One of two categories of sunscreens, chemical sunscreens rely on molecules that seep into the skin, absorb UV radiation, and release it as heat. These formulas take 20 to 30 minutes to kick in. Once they’ve absorbed too much UV radiation, the molecules decompose and the sunscreen stops working just about immediately, Johnson explains.

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