UV Index Explained: What the Numbers Mean for Your Skin

0-2 (Low): Minimal danger. You can be outdoors without sunscreen for short periods. Sunburn is unlikely unless you are very fair-skinned.

3-5 (Moderate): Sunburn is possible in 30 minutes for fair skin. SPF 30+ recommended. Seek shade around midday.

6-7 (High): Sunburn in 15-20 minutes for fair skin. SPF 30-50 essential. Hat and sunglasses strongly recommended.

8-10 (Very High): Sunburn in under 15 minutes. SPF 50+, protective clothing, and shade are all necessary. Limit midday outdoor time.

11+ (Extreme): Sunburn in under 10 minutes. Avoid outdoor exposure between 10am and 4pm if possible. Full protection required.

UV intensity peaks between 10am and 4pm, with the absolute maximum around solar noon (roughly 1pm during daylight saving time). UV is strongest in summer, at higher altitudes, near the equator, and on surfaces that reflect UV (snow, sand, water, concrete).

A practical rule: if your shadow is shorter than you are, UV is intense. If your shadow is taller than you, UV is lower.

Up to 80% of UV radiation penetrates thin cloud cover. Scattered clouds can actually increase UV through scattering effects. Only thick, dark storm clouds significantly reduce UV.

This is why sunburns on overcast days are so common — people skip sunscreen because it looks gray, but the UV index can still be high.

Your Fitzpatrick skin type determines how quickly UV damages your skin. Type I (very fair, always burns) may burn in 10 minutes at UV 8. Type IV (olive, rarely burns) may tolerate 40 minutes at the same UV level before burning. But UV damage accumulates at all skin types — tanning is itself a sign of DNA damage.

Use our Skin Type Quiz to determine your type and get personalized UV protection recommendations.

Check the UV index on your weather app every morning. At UV 3+, apply sunscreen before leaving the house. At UV 6+, plan outdoor activities for early morning or late afternoon. At UV 8+, minimize direct sun exposure and wear protective clothing.

For children: be extra cautious — one blistering sunburn in childhood doubles lifetime melanoma risk. At UV 3+ apply SPF 30+ to any exposed skin and make hats non-negotiable.

Burn time isn't fixed — it scales with UV index, your skin type, and the SPF you applied. A fair-skinned person at UV 8 will burn in roughly 35 minutes unprotected; SPF 50 (applied correctly) extends that into hours, but lab numbers assume the full dose, which most people never apply.

Use the Sunscreen Calculator at /tools/sunscreen-calculator/ to see Diffey-model burn-time, the right reapply interval (120 min outdoors, 80 min in water), and the per-zone amount you should actually be putting on. The calculator pairs the UV index numbers above with your skin type and SPF to give a single, practical recommendation.