When you are most at risk from UV

You get more UV, and sunburn faster, when the sun’s rays are strongest. The UV index is a good guide to the strength of the sun’s rays, but the amount of UV you receive can also depend on other factors, such as the surface you are standing on, and the amount of time you spend in the sun.

Check the UV Index regularly, you will find that it is higher, and that you are more at risk:

  • In spring and summer (April to September). The Index is lower in the fall and lowest in the winter.
  • In the middle of the day. When the sun is highest in the sky.
  • When the sky is clear and sunny. A thick layer of heavy cloud can reduce UV, but thin, light or scattered clouds do not block UV. The sun’s rays may not feel hot under thin clouds, but they can still burn.
  • If you travel farther south. The Index is highest at the equator, and lowest at the poles. (Even though UV is very low at the poles, it can still be a concern if you are outdoors for long periods of time, as the sun is low in the sky and can reflect off the snow.)
  • When the ozone layer is thinner. The thickness of the ozone layer in the upper atmosphere changes naturally from day to day. In addition, the ozone layer over Canada still experiences minor depletions from the use of industrial chemicals.

Other factors that can increase your risk: 

  • Snow, dry sand, and concrete. These light-colored surfaces reflect the sun’s rays like a mirror, increasing the amount of UV that you receive. Fresh, white snow can almost double your exposure! Be sure to wear sunglasses to protect your eyes against reflected UV.
  • Spending too much time in the sun. The longer you are out in the sun, the more UV you receive. Staying in the shade can reduce your exposure to UV by 50% or more.
  • Mountains. mMre UV reaches higher altitudes, where the air is thinner and clearer. 

Did you know?

  • Even if it’s cool outside, you can still burn.  UV can be high on a cool day in summer, or on a warm day in the spring. Check the UV Index to be sure. You can even get sunburned in winter, when the UV Index is low: fresh white snow reflects the sun’s rays, and can more than double the amount of UV that you receive. 
  • Window glass does not provide full UV protection. It filters out UV-B but not UV-A. You can still get a sunburn. It just takes longer.
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