What Is the UV Index?
The UV Index is an internationally standardised scale for the strength of ultraviolet radiation from the Sun at a particular place and time. It is weighted for the wavelengths most likely to damage skin, so it is a guide to the risk of sunburn and longer-term harm to the skin and eyes.
The scale starts at 0 and has no fixed upper limit. A higher number means stronger UV and a greater risk from unprotected exposure. Values of 11 or more are classed as extreme.
A current UV Index describes conditions at that time. A daily forecast usually reports the highest value expected around solar noon. Check which one you are viewing before planning time outdoors.
UV Index Levels
UV Index Level What to Do 0–2 Low Protection is usually not needed for brief exposure. Sunglasses can help on bright days, especially near snow or water. 3–5 Moderate Seek shade around solar noon. Cover exposed skin and use sunscreen. 6–7 High Reduce time in direct sun around solar noon. Use shade, clothing, a hat, sunglasses, and sunscreen. 8–10 Very High Extra protection is needed. Plan outdoor activities away from the strongest midday UV where possible. 11+ Extreme Avoid direct midday sun where possible and use several forms of protection outdoors.Use sun protection when the UV Index reaches 3. How quickly skin burns is not a fixed countdown: it varies with skin type, UV strength, exposure history, medicines, altitude, reflected radiation, clothing, and sunscreen use. Darker skin can take longer to burn, but it can still suffer UV damage.
What Affects UV Levels?
The UV Index can be high even when the air feels cool. Several factors determine how much ultraviolet radiation reaches the ground:
Time of day: UV is generally strongest during the four hours around solar noon. Morning and late-afternoon levels are usually lower.
Season: In the middle latitudes, UV is usually stronger in summer than in winter. Closer to the equator, high levels can occur throughout the year.
Altitude: UV increases with elevation because there is less atmosphere above you to absorb it. Mountain locations and ski areas can therefore have strong UV even in cold weather.
Cloud cover: Thick cloud often reduces UV, but thin or broken cloud may still allow a large amount through. Under some cloud patterns, scattering can briefly raise UV at the surface. Read more about how cloud cover affects the weather you experience.
Reflective surfaces: Snow, water, sand, and other bright surfaces can reflect UV towards your skin and eyes, increasing your total exposure.
Latitude and ozone: The Sun sits higher in the sky nearer the equator, giving its rays a shorter path through the atmosphere. The amount of ozone overhead also affects how much UV reaches the surface.
Forecast models combine these factors to estimate the UV Index. Our guide to how weather forecasts work explains why local predictions can change as the input data changes.
How to Protect Yourself
At a UV Index of 3 or above, combine several forms of protection rather than relying on sunscreen alone:
- Seek shade, especially around solar noon. Remember that trees and umbrellas do not block all scattered or reflected UV.
- Wear closely woven clothing, a wide-brimmed hat, and wraparound sunglasses that protect against UVA and UVB.
- Apply broad-spectrum SPF 30 or higher sunscreen generously to skin that clothing does not cover.
- Follow the product instructions and reapply at least every two hours, as well as after swimming or sweating.
- Do not use sunscreen to extend the time you spend in direct sun.
- Give children extra protection because UV damage accumulates over a lifetime.
If your shadow is shorter than you are, the Sun is high and UV is likely to be stronger. It is a useful prompt to find shade, but the local UV Index gives you the better guide.
How Airpult Shows the UV Index
Airpult shows the UV Index for your location on the forecast page, using colours from green for low levels to purple for extreme levels. Check whether you are looking at the current value or the forecast peak, then use the protection guidance for the expected level. Find a location to check the UV Index.
