TAMPA, Fla. (WFLA) — Summer is fast approaching and the UV index is increasing back to those ‘extreme’ levels. The UV index is a measure of the sun’s harmful ultraviolet radiation reaching the surface that can cause skin damage.

While there are multiple factors that affect the UV index every day, the sun angle or how high the sun is in the sky, is critical. In general, the higher the sun is in the sky, the easier your skin can burn, causing skin damage after exposure.

Two things in particular affect the sun angle: the time of the day and the time of the year.

In the winter months, the sun angle is lower in the sky every day because of the tilt of the earth, meaning the UV index is lower by default. During the summer months when the northern hemisphere is tilted toward the sun, the sun angle is much higher in the sky. That’s one main reason the UV index is much higher this time of the year.

The time of the day affects it as well and is the most important factor here in Florida. In the early morning hours the UV index is very low. It is highest during the middle of the day when the sun is more directly overhead.

Unless you’re constantly looking up the forecast, it is not easy to know what the UV index is, and it’s hard to tell if you need to wear sunscreen.

Instead, it is easy to use your shadow length to determine how long you have to be exposed to the sun’s rays before skin damage can occur. The longer or taller your shadow, the longer it takes for skin damage to occur and vice versa.

Just after sunrise, your shadow is very long. When your shadow is more the twice your height, it takes a very long time for the UV rays to cause damage to your skin, making sunscreen unnecessary.

As the morning goes on and the sun gets higher in the sky, your shadow starts to shorten up. When your shadow is shorter than your body length, sun burn can happen in less than 30 minutes.

When the sun is directly overhead and your shadow is less than half your height, skin damage can occur in as little as 10 to 15 minutes.