UV radiation doesn't take a rest day. At altitude, on snow, on water, or even through cloud cover, UV exposure during outdoor activities is significantly higher than most people realise. A single bad burn isn't just painful — cumulative UV damage is the leading cause of skin cancer worldwide. The right sunscreen, used correctly, is as essential as any other piece of kit.
Understanding SPF
SPF (Sun Protection Factor) measures how well a sunscreen protects against UVB rays — the ones that cause sunburn. Here's what the numbers actually mean:
- SPF 15 — blocks 93% of UVB rays
- SPF 30 — blocks 97% of UVB rays
- SPF 50 — blocks 98% of UVB rays
- SPF 50+ — blocks 98–99% of UVB rays
For outdoor activities, we recommend SPF 30 at minimum, SPF 50 for alpine, snow and water environments. The difference between SPF 15 and SPF 30 is meaningful; the difference between SPF 50 and SPF 100 is marginal.
UVA vs UVB — Why Broad Spectrum Matters
UVB rays cause sunburn. UVA rays penetrate deeper into the skin and cause long-term ageing and contribute to melanoma. Standard SPF ratings only measure UVB protection. Always choose a broad-spectrum sunscreen — one that protects against both UVA and UVB.
Look for these UVA-protecting ingredients: zinc oxide, titanium dioxide (physical/mineral), or avobenzone/tinosorb (chemical filters).
Mineral vs Chemical Sunscreens
| Type | How It Works | Best For | Notes |
|---|---|---|---|
| Mineral (zinc/titanium) | Reflects UV rays off skin | Sensitive skin, coral reef areas, children | Can leave white cast; reef-safe |
| Chemical (organic filters) | Absorbs UV energy and converts to heat | Athletes, everyday use | Applies invisibly; apply 20 min before sun exposure |
Water Resistance
No sunscreen is truly "waterproof" — in most countries, this claim is no longer permitted on labels. "Water resistant" sunscreens maintain their SPF for either 40 or 80 minutes of water exposure. For swimming, surfing or heavy sweating, choose an 80-minute water-resistant formula and reapply immediately after towelling dry.
How Much & How Often
Most people apply far too little. Studies consistently show the average person applies only 25–50% of the required amount, meaning their effective SPF is much lower than the label states.
- Face: about ½ teaspoon (2.5ml)
- Body (full coverage): about 35ml — a shot-glass full
- Reapply every 2 hours, or immediately after swimming or heavy sweating
- Apply 15–20 minutes before sun exposure (chemical sunscreens need time to bind)
"At 3,000m altitude, UV intensity is approximately 25% higher than at sea level. On snow, up to 80% of UV radiation is reflected back at you. Factor both into your sun protection strategy."
Don't Forget These Easy-to-Miss Spots
- Ears and back of the neck
- Lips (use a dedicated SPF lip balm)
- Tops of feet and ankles
- Bald spots and hair parting
- Back of hands
- Under chin (reflected UV from water and snow hits upward-facing skin)
Sunscreen is not a luxury item. Combined with quality sunglasses, a sun hat and UPF-rated clothing, it's the foundation of any sensible outdoor skincare routine. Put it on, reapply it, and go enjoy the sun — safely.
