The UV index is a forecast of the strength of the sun’s ultraviolet radiation at the surface, on a scale that starts at 0. In the United States, the National Weather Service’s Climate Prediction Center produces the forecast and the EPA publishes it by ZIP code. Higher numbers mean skin and eyes can be damaged faster.
Exposure categories
| UV index | Exposure level (WHO) |
|---|---|
| 0–2 | Low |
| 3–5 | Moderate |
| 6–7 | High |
| 8–10 | Very high |
| 11+ | Extreme |
EPA sun protection advice
- 1–2 (low): no protection needed; you can safely stay outside using minimal sun protection.
- 3–7 (moderate to high): protection needed. Seek shade during late morning through mid-afternoon. Use broad-spectrum sunscreen of at least SPF 15 on exposed skin, and wear protective clothing, a wide-brimmed hat and sunglasses.
- 8+ (very high to extreme): extra protection needed. Be careful outside, especially during late morning through mid-afternoon. If your shadow is shorter than you, seek shade and wear protective clothing, a wide-brimmed hat and sunglasses, and use broad-spectrum SPF 15+ sunscreen.
The shadow rule
A quick check without a forecast: if your shadow is taller than you, UV exposure is likely lower (early morning, late afternoon). If your shadow is shorter than you, exposure is higher, which usually happens around midday.
When UV peaks
UV is strongest around solar noon, when the sun is highest. Each city UV page shows the hourly forecast and that day’s solar noon.
Sources: EPA UV Index Scale; NOAA Climate Prediction Center UV Index.