The UV index is a single number that summarizes how strong sunburn-producing UV radiation is at a given place and time. The WHO scale runs from 0 to 11+, and each range comes with its own protection rules.
The 5 Levels
| Index | Category | Protection |
|---|---|---|
| 0–2 | Low | none for most; sunglasses on bright days |
| 3–5 | Moderate | SPF 30, hat, midday shade |
| 6–7 | High | SPF 30–50, cover up, shade 11–16 |
| 8–10 | Very high | SPF 50+, extra protection, avoid midday |
| 11+ | Extreme | full protection, avoid sun if possible |
How Skin Type Changes Burn Time
At UV index 7, fair skin (type I) burns in ~15 minutes; type II ~20 min; type III ~30 min; type IV ~50 min; types V–VI ~80+ min. Multiply by SPF to estimate safe time: SPF 30 × 15 min = 7.5 hours in theory — but reapply every 2 hours anyway.
What Raises the Index Locally
- altitude: +10–12% per 1000 m;
- reflection: snow up to +80%, sand +15–25%, water +10–30%;
- ozone holes: can push index 1–2 points higher;
- clouds: thin clouds reduce UV only 10–30%, thick overcast up to 70%.
Bottom Line
Know your number: check the live UV index for your city every morning. Below 3 — relax; 3–5 — SPF 30; 6+ — SPF 50+ and strict shade at midday. The scale is your daily sun-safety compass.