UV Safety

Snow, Altitude, and 'Snow Blindness' — Why Winter UV Bites

Snow reflects up to 80% of UV and altitude adds ~10% per 1000m. Why winter sports demand summer-grade sun protection.

Skiers, climbers, and polar workers regularly burn in subfreezing temperatures. The reason: snow's albedo plus thinner atmosphere can push effective UV well above what the forecast number suggests.

The compounding factors

  • Fresh snow albedo: +50–80% reflected UV (WMO)
  • Altitude: ~+10–12% UV per 1000m gain
  • Thin clouds: 70–90% UV passes through

Photokeratitis ('snow blindness')

UVB sunburn of the cornea — painful, temporarily blinding, fully preventable with category-3 or category-4 sunglasses or ski goggles. Symptoms appear 6–12 hours after exposure (AAO).

Sunscreen choice

Sweat- and water-resistant SPF 50+ on all exposed skin including under the chin and nose (where reflected UV hits). Reapply every 2 hours; lip balm with SPF 30+ is non-optional.

Key takeaways

  • Snow + altitude can double effective UV.
  • Use category-3 sunglasses or goggles.
  • SPF 50+ everywhere, including under-chin.

Related DermUV pages

Using Snow, Altitude, and 'Snow Blindness' — Why Winter UV Bites in practice

UV strength on this page follows solar elevation, ozone thickness, cloud cover, altitude, and surface reflection. Snow can bounce back most of the UV that hits it, water and sand far less, but all of them add to the dose skin receives.

Burn-time figures come from minimal erythemal dose (MED) values published for each Fitzpatrick skin type, divided by the erythemal irradiance at a given UV index. Personal MED varies by roughly 20 percent, so treat every number as a planning range.

Reapplication matters more than the SPF number. Reapply roughly every two hours outdoors and immediately after swimming, heavy sweating, or towelling, regardless of what the bottle claims.

Cumulative dose drives photoaging and long-term skin damage more than any single day. Small daily exposures on commutes, walks, and driving add up across a season.

Plan outdoor blocks around the peak UV window, usually between 10am and 4pm local time. Shade, UPF fabric, a wide-brim hat, and UV-blocking sunglasses reduce dose more reliably than sunscreen alone.

UV scale reference

The WHO scale groups UV 1-2 as low, 3-5 as moderate, 6-7 as high, 8-10 as very high, and 11 or above as extreme. Protection is recommended from UV 3 upward, and shade during the middle of the day becomes the priority from UV 8 upward.

A practical routine at moderate-to-high UV is roughly one ounce of broad-spectrum sunscreen for full-body coverage, applied 15 minutes before going out, then reapplied on schedule. Clothing, hats, and shade carry the rest of the load, especially for children and anyone with a history of easy burning.

Keep exploring DermUV

These pages give more depth around snow, altitude, and 'snow blindness' — why winter uv bites, from UV-scale reference material to calculators and city forecasts.

Numbers are modelled, not measured at your exact location, so treat them as guidance for planning rather than exact thresholds.