The Altitude Rule: Why UV Hits Harder for Hikers and Skiers
Every 1,000 meters you climb, UV intensity rises about 10% — which is why a sunny summit can scorch you faster than the beach.
UV levels increase by approximately 10% for every 1,000 meters (about 4-5% per 1,000 feet) of elevation gain because the thinner atmosphere filters less radiation.
The World Health Organization notes that UV intensity climbs with altitude as the atmosphere thins, which is why exposure at elevation can be substantially higher than people expect at sea level.
Questions we get a lot
How much stronger is UV at high altitude?
UV intensity increases by approximately 10% for every 1,000 meters of elevation gain, or about 4-5% per 1,000 feet. This happens because the thinner atmosphere at altitude filters out less UV radiation. That is why hikers and skiers can burn faster up high than at sea level.
How should hikers and skiers protect against UV at altitude?
Apply broad-spectrum sunscreen generously and reapply often, since UV is stronger at elevation. Snow and ice also reflect UV onto exposed skin, including under the chin and nose. Add UV-blocking sunglasses or goggles, a brimmed hat, and protective clothing for full coverage.
r/Ultralight: 'I got fried on a high alpine pass even though it wasn't that hot — is UV really that much stronger up there?'