SolriseUV index explained: what each level means
The UV index is a 0 to 11+ scale for how strong the sun's ultraviolet radiation is right now, and how quickly it can damage skin. At 3 and above it is worth using protection around midday, and at 6 or above unprotected skin starts burning in under an hour.
What the UV index is
The UV index turns the strength of the sun's ultraviolet radiation into one simple number. The higher the number, the faster unprotected skin and eyes can be damaged. It is published on a shared international scale, the WHO Global Solar UV Index, so a 7 means the same thing in Phoenix, Sydney, or Madrid.
The UV index scale
| UV index | Level | What it means |
|---|---|---|
| 0 to 2 | Low | Little risk for most people. No protection needed. |
| 3 to 5 | Moderate | Seek shade around midday. Sunscreen, hat, and sunglasses help. |
| 6 to 7 | High | Protection needed: shade at midday, cover up, sunscreen. |
| 8 to 10 | Very high | Extra protection. Avoid being outside in the middle of the day. |
| 11 and up | Extreme | Extra protection. Unprotected skin burns quickly. |
Source: WHO Global Solar UV Index exposure categories.
Why the UV index changes
UV is highest with the sun directly overhead, which is why it peaks around midday and in summer. It is also higher on clear days, at higher elevation, and near reflective surfaces like snow or water, which bounce extra UV back at you.
Clouds lower it, but not as much as most people think. Even under heavy cloud you can still sunburn, so a gray sky is not a reason to skip sunscreen on a long day outside.
What the UV index means for you
Everyday
6 or above means unprotected skin starts burning in under an hour at midday, so plan sunscreen or shade accordingly. An early morning or evening walk or run cuts UV exposure dramatically compared to going out at midday, even on a day with the same forecast index.
Outdoors
Reapply sunscreen about every two hours on long outings, and sooner after sweating or swimming. Above treeline, on snow, or on water, treat the UV index as higher than the number shown, and wear sunglasses. Cloudy days still count: keep sunscreen on for long outings even when the sun is hidden.
Reading the forecast
Look at the hourly UV, not just the daily peak. The number climbs through the morning, tops out around solar noon, and falls through the afternoon, so the same day can be Low at 8 a.m. and Very high at 1 p.m. Moving a run or a yard job a couple of hours earlier is often the simplest protection there is.
Common questions
What UV index do you need sunscreen?
On the WHO scale, from 3 (Moderate) up it is worth seeking shade around midday and using sunscreen, a hat, and sunglasses. At 6 or above, unprotected skin can start burning in under an hour at midday.
Can you get sunburned on a cloudy day?
Yes. Clouds lower UV, but even under heavy cloud you can still sunburn, so keep sunscreen on for long outings.
Why is UV higher on snow or water?
Reflective surfaces bounce UV back at you. Fresh snow can reflect up to 80% of UV rays, according to the US EPA.
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