The Best Time to Avoid the Sun

As a simple rule, avoid direct sun between 10 a.m. and 4 p.m. That six-hour window is when UV is strong enough to burn you fastest.

Why midday is the problem

UV strength depends on the angle of the sun. When the sun is low, near sunrise and sunset, its light passes through more of the atmosphere, which filters out a lot of the UV. When the sun climbs high overhead around midday, the light takes a shorter path down and hits you with much more UV.

That is why the UV index traces a hump through the day: near zero at dawn, rising through the morning, peaking around solar noon, then falling back to zero after sunset.

The 10 a.m. to 4 p.m. rule

Health bodies settled on 10 a.m. to 4 p.m. as an easy way to remember the risky window. In that stretch, most of the day's UV arrives. Outside it, the sun is usually gentle enough for most people, though on extreme-UV days you should still be careful.

One catch: daylight saving time shifts the clock. Solar noon, the true peak, lands closer to 1 p.m. in summer than 12 p.m. So the strongest sun is often in the early afternoon, not exactly at noon.

The shadow test

You do not need an app to gauge risk. Look at your shadow. If your shadow is shorter than you are tall, the sun is high and UV is strong, so seek shade. If your shadow is longer than you, the sun is lower and UV is weaker. It is a rough guide, but a handy one.

Plan your day around UV

• Schedule runs, walks, and yard work for before 10 a.m. or after 4 p.m.
• Take a shade break during the midday peak rather than powering through it.
• At the beach or pool, remember water reflects UV, so the peak hours hit harder.
• On extreme-UV days, treat even the shoulders of the window with care.

Frequently asked questions