Sunburn is more severe at high altitudes due to the thinning of the Earth's atmosphere, which acts as a natural filter for ultraviolet (UV) radiation. For every 1,000 meters (approx. 3,280 feet) of elevation you gain, UV levels increase by about 10% to 12%. This is because there are fewer air molecules, less water vapor, and less ozone above you to absorb and scatter the sun's harmful rays. Consequently, a person skiing at 3,000 meters in the Alps or hiking in the Rockies is exposed to roughly 30-40% more intense UV radiation than someone at sea level on the same day. Additionally, the cool air and wind at high altitudes can be deceptive; you may feel chilled and not realize your skin is burning until the damage is already done. Furthermore, surfaces common at high altitudes—such as snow and ice—can reflect up to 80% of UV radiation back upward, essentially doubling your exposure by hitting areas like the underside of your chin or nose. In 2026, dermatologists recommend high-SPF "mountain-grade" sunscreens for any high-altitude activity, even on overcast days.