Insider: How the UV index can predict your next sunburn

Maybe you can’t always feel the sun’s rays, but your skin will definitely react to them. Depending on the UV index, it could take only a handful of minutes to burn. 

According to the EPA, the UV Index was designed to help people take daily precautions based on how intense the sun’s radiation is at ground level. It’s a number scale from 0 to 11+, where anything higher than 6 means your skin could be in danger. 

Let’s be clear, the temperature has no effect on the UV index. Oftentimes, a higher UV will occur on days where the temperature is warmer. However, these things aren’t closely related.

Here’s a cheat sheet according to NOAA.

UV 3–4: 45 mins to burn

UV 5-6: 30 minutes

UV 7-9: 20 minutes

UV 10+: Less than 15

UV rays can still be dangerous on cool or cloudy days because UV radiation, not temperature, causes sunburn. So what does protect you?

Sunscreen. According to the EPA, look for products labeled "broad-spectrum" with an SPF of at least 30. SPF 30 blocks about 97% of UVB rays, but only if applied generously and often—and most people don’t.

SPF math can be tricky. According to the EPA, SPF 15 is not half the protection compared to SPF 30. Instead, if your skin starts to burn in 10 minutes, SPF 30 extends that to about 300 minutes, but only if you use a full ounce and reapply every 2 hours.

Summer shows the greatest UV index typically because the sun reaches its highest point in the sky. It's at its steepest angle, so it cuts through the atmosphere quicker, meaning the ozone layer does little to protect your skin from radiation.

The UV strikes the worst around midday, that’s right whenever the sun is highest in the sky and can easily cut through the atmosphere and upper level ozone - a key ingredient to blocking harmful UV rays. In Columbia, hourly forecasts from the EPA show the UV Index peaking around 1 or 2 PM nearly every day in summer.

According to the EPA, even surfaces like water, sand, and pavement can reflect UV rays and increase your exposure. That’s why hats, sunglasses, and long sleeves matter just as much as sunscreen. The bottom line is the UV Index isn’t just a number—it’s a burn timer.