UV index: what does it mean and which values are dangerous?
The UV index describes the strength of sunburn-producing ultraviolet radiation at the Earth's surface. It is not a temperature scale: a cool, clear spring day can have a high UV index, while a hot but heavily overcast day may have a lower one.
The UV index scale
| UV index | Risk | Recommended protection |
|---|---|---|
| 0–2 | Low | Protection is usually not necessary. |
| 3–5 | Moderate | Sunglasses, shade around midday and SPF 30 sunscreen. |
| 6–7 | High | Cover exposed skin, use SPF 30–50 and limit midday sun. |
| 8–10 | Very high | Seek shade; use SPF 50, a hat and protective clothing. |
| 11+ | Extreme | Avoid direct sun around midday whenever possible. |
Why does UV matter?
UV radiation can damage skin cells before the skin feels hot. Repeated exposure increases premature skin ageing and the risk of skin cancer; strong exposure can also harm the eyes. Children and people with fair skin generally burn faster, but every skin type can be damaged.
Practical protection
- Check the daily peak, not only the current value.
- Apply broad-spectrum sunscreen generously and reapply after swimming or heavy sweating.
- Clothing, a wide-brimmed hat and shade provide more reliable protection than sunscreen alone.
- Cloud does not eliminate UV; thin cloud may still allow much of it through.
Frequently asked questions
From which value is the UV index dangerous?
Protection is recommended from UV 3. At UV 6 and above, unprotected fair skin can burn quickly around midday.
Can you get sunburned in the shade?
Yes. Reflected and scattered UV reaches the shade, especially near water, pale paving or sand.
Does SPF 50 last all day?
No. Sunscreen wears off and must be reapplied according to its instructions, especially after swimming, towelling or sweating.