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Trail sunburn is a sneaky injury: the air is cool, the breeze feels pleasant, and by the time skin feels hot the burn is already developing. Mountains make it worse in three ways most hikers do not expect: UV rises roughly 10-12% per 1,000 m of altitude, snow and pale rock reflect UV from below, and cloud cover gives a false sense of safety while still letting most UV through. This guide covers the basics of burn risk on the trail and the protection routine that actually works — sunscreen as the backup, not the primary defence, with clothing, timing and reapplication doing the heavy lifting. It is educational background, not medical advice; treat any serious burn properly and seek help for blistering, fever or confusion.
Understand UV burn risk on the trail — altitude, water and snow reflection multiply exposure, and a day hike can easily deliver a serious burn before you notice.
Three multipliers stack up: thinner air at altitude lets more UV through (roughly 10-12% more per 1,000 m), snow and water reflect up to 80-90% of UV back at you, and cool mountain air hides how much exposure you are accumulating.
Yes. Thin cloud still lets most UV through, and overcast mountain days regularly produce burns — especially above the snow line where reflection adds exposure from below. If the UV index is 3 or higher, protect, whatever the sky looks like.
Every two hours, and sooner after heavy sweating or any water contact — trail sunscreen is constantly being washed off by sweat. Apply SPF 30+ broad-spectrum to all exposed skin 15-30 minutes before you start, and cover the easy-to-miss spots: ears, lips, neck and the tops of your feet.
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