The hotter it is outside, the more sunscreen we lather on. Seems logical. But there is more information in our local weather forecasts that we should pay attention to as far as skin safety is concerned.

We often hear random numbers associated with something called the ultraviolet index, more commonly called the UV index. It is an international standard of measurement of the strength of the sun’s ultraviolet rays at a particular place and time. The UV index was developed in 1992 by Canadian scientists and, in 1994, was adopted by the UN’s World Health Organization and World Meteorological Organization. Cool, huh?

The index, as you might already know, delivers information on an open-ended linear scale, directly proportional to the intensity of UV radiation that causes sunburn.  

It works something like this:

If the UV index is 0.0 – 2.9, the green zone, it means the average person is in low danger for sunburn. Precautions include wearing sunglasses on bright days and, if you burn easily, war SPF 30+ sunscreen.

If the UV index is 3.0 – 5.9, the yellow zone, it means there is moderate risk of harm from unprotected sun exposure. Wear SPF 30+ sunscreen and reapply every two hours, especially after swimming or sweating. Wear those sunglasses.

If the UV index is 6.0 – 7.9, the orange zone, it means there’s a high risk of harm from unprotected sun exposure. In addition to following the above safety precautions, try to stay out of the sun between 10 a.m. and 4 p.m.

If the UV index is 8.0 – 10.9, the red zone, it means there’s a very high risk of harm from unprotected sun exposure. In addition to wearing sunglasses, applying sunscreen, and staying out of the sun during its strongest time, wear those wide-brim hats as well as sun-protective clothing.

If the UV index caps out at 11.0+, which is the violet zone. Follow all precautions, as well as stay out of the sun as much as you can as you are at extreme risk of harm. This zone is rare in Canada, but it can reach as much as 14 in the tropics and southern states so do take care on your travels!

If you’d like to see records of Canadian places that hold the UV Index highs over the years, check out this study.

If you don’t remember having to be so concerned about UV rays while growing up – if you were in Canada – you’re right. The record ozone loss in the Arctic has been caused by ozone-destroying chemicals such as chlorofluorocarbons and halons left over from before the Montreal Protocol, the international agreement signed in 1987 to phase out those chemicals (think refrigerators, aerosol spray cans, etc.). If you’d like to read more about efforts to save the ozone, check out this article in The Conversation.