UV Index Guide

Understand UV index levels, sun exposure risk, and how long before sunburn at each UV level.

UV Index (from weather app or Met Office)

Skin type

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How This Works

UV Index is a WHO standard scale measuring ultraviolet radiation intensity (1–11+). Time to sunburn varies by UV intensity and Fitzpatrick skin type. SPF (Sun Protection Factor) theoretically multiplies burn time — SPF 30 means 30× longer before burning. However, no sunscreen blocks 100% of UV and SPF effectiveness degrades with sweat, towelling and water. Reapplication every 2 hours is essential regardless of SPF rating.

Yes — clouds block visible light but pass significant UV radiation. A thin overcast can still allow 70–90% of UV through. In the UK, UV index routinely reaches 5–7 during summer (May–August) even on overcast days. The "it's cloudy so I don't need sunscreen" assumption causes many British sunburns. Check the Met Office UV forecast at metoffice.gov.uk before outdoor activities.