You may be aware that you have to wear sunscreen even when it doesn’t “look sunny” outside. That’s because sunscreen is meant to protect you from more than the sun’s most visible rays.

Don’t make the mistake of thinking that sun tans and sun burns are the only issue. Sunscreen is meant to protect you from UV radiation and its unpleasant side effects: aging skin and an increased risk of sun cancer.

Getting yourself maximum protection is about more than making a visual check of today’s weather conditions. It’s about knowing when to avoid outdoor weather altogether, as this story from ABC News demonstrates.

The story showcased the Ultra-Violet Index. This is a forecast run by the National Weather Service noting places where UV radiation is particularly strong. You can run a search for local UV conditions by zip code in order to get your local forecast.

The index runs from 1 (low) to 11+ (extreme). It’s also color coded, with green indicating low burn times, yellow indicating medium burn times, orange indicating high burn times and red indicating extreme burn times.

According to ABC, “on a day when the UV Index is ‘extreme,’ it takes less than 15 minutes to get burned.”

You can mitigate exposure with protective clothing and a sunscreen rated at SPF 30 or higher. However, on High-to-Extreme UV index days your skin might just thank you for staying out of the sun entirely! If you want younger, healthier skin, make sure to check the index every day.