What UV index do you burn at?
Most people start to risk sunburn at UV index 3 — that's the WHO's protection threshold. Below 3, burning is unlikely for all but the fairest skin, even over a long afternoon. Above it, time-to-burn shrinks fast: fair skin burns in under an hour at UV 3–5 and in roughly 15–25 minutes at UV 8.
Time to burn by skin type
| Skin type | UV 3 | UV 5 | UV 8 |
|---|---|---|---|
| I — Very fair | ~44 min | ~27 min | ~17 min |
| II — Fair | ~56 min | ~33 min | ~21 min |
| III — Medium | ~1h 20m | ~47 min | ~29 min |
| IV — Olive | ~1h 40m | ~1h | ~38 min |
| V — Brown | ~2h 15m | ~1h 20m | ~50 min |
| VI — Dark brown / black | ~3h 40m | ~2h 15m | ~1h 25m |
Estimates based on typical minimal erythemal doses per Fitzpatrick type (methodology). Water, sand, snow, and altitude shorten these times. See the full burn time chart for every UV level.
The practical version
- UV 1–2: no protection needed for a typical day, any skin type.
- UV 3–5: fair skin (types I–III) needs SPF for extended midday time outside.
- UV 6–7: everyone should protect for midday exposure; fair skin burns in ~20–40 min.
- UV 8+: fair skin burns in a coffee break. Shade, hat, SPF 50, no exceptions.
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