UV Index: Where Colorado ranks

UV rays are at their worst in summer at high noon, with averages in Denver exceeding 10 — which is borderline "extreme."

Why it matters: That's why especially important to limit time in the sun and cover up.

• UV radiation causes sunburn and is a risk factor for skin cancer.

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.