Jun 19, 2025 - Health
UV index: When and where it's highest
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In the U.S., UV rays are at their worst at high noon in the summer, with average values exceeding 11 — considered "extreme" — in some places.
Why it matters: That's when it's especially important to limit time in the sun and cover up.
- UV radiation causes sunburn and is a risk factor for skin cancer.
By the numbers: A UV index of 6-7 is the "high" range, 8-10 is "very high."
Between the lines: Altitude, latitude, cloud cover, ozone level, time of day and seasons all factor into the UV index.
It's a myth that you can't get a sunburn when it's cloudy — and that you need to feel the sun's hot rays to get a sunburn.
- In reality, 80% of solar UV radiation can penetrate light cloud cover — and infrared heat is different from UV radiation (which you can't feel), according to the EPA.
A simple way to estimate your UV exposure: Look at your shadow.
- If it's shorter than you are (around midday), UV levels are higher and more likely to cause sunburn.
