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How much sun is too much sun?

While some sunlight is beneficial, an overabundance of it can be harmful due to the negative effects of ultraviolet (UV) radiation. These invisible rays of sunlight are able to cause skin damage, and they are a proven human carcinogen.
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​Skin cancer is the uncontrolled growth of abnormal skin cells, and although it’s the most prevalent form of all cancers, skin cancer has increased significantly among men and women during the last 25 years. UV radiation causes about 90 per cent of melanoma cases in Canada.  

“The good news is there are plenty of ways you can protect yourself from harmful UV radiation,” says Dr. Harvey Lui, a dermatologist at the BC Cancer Agency. “The bad news is that most people are not paying enough attention to protecting themselves.”

Case in point: what do the ratings on a UV Index tell you about the danger of sun exposure? Chances are that if you’re like most people, according to a recent Canadian Cancer Society survey, you’re probably not so sure.  

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The UV index

The UV index is a measure of the amount UV radiation. The values of the index range from zero and upward, with a higher UV index signalling a greater potential for damage to the skin and eyes, with more harm occurring in less time.

UVI from CCS.jpgMany things contribute to the index, but the main factors are the amount of sunshine, the solar angle, the amount of ozone in the atmosphere, elevation and the reflectivity of the ground surface. 

Technically, the UV index goes to infinity, but for most places that humans inhabit, it is usually below 12. (The highest UV ever recorded on Earth was apparently 43.3 in Bolivia on a volcano, during the peak of summer.) 

"For all practical purposes, my advice is the same for all ratings of UV index 3 and above," says Dr. Lui. "Avoid going outside during the hours of the most intense sunshine, between 11am and 3pm, and if you do go outside, seek shade, cover-up and wear sunscreen on exposed skin."

What about vitamin D?

Despite the risks, many Canadians think exposure to UV is good for them, with almost half of Canadians believing that the sun is the safest way to get vitamin D.

Exposing your skin to a small amount of UV light can contribute to the body's process of vitamin D synthesis, and some research has shown that having adequate levels of vitamin D can help protect against cancer. However, you don't have to spend hours in the sun to get enough vitamin D.

“Standing or walking outside without a hat and with your arms exposed for about 10 to 15 minutes each day is just about as much time as most people will ever need for their skin to make adequate amounts of vitamin D,” says Dr. Lui, adding that whatever extra vitamin D your skin makes also gets broken down by the sun’s UV rays. 

“Sunlight can both make vitamin D and degrade it as well. The only thing that you build up by hanging out in the sun for a long time is DNA damage, and your risk of getting skin cancer.” 

How to protect yourself

“The truth is that sunscreen should really be your last line of defence,” says Dr. Lui. “It’s like driving: just because you have seat belts and air bags doesn’t mean you should drive recklessly.”

In other words:
  • limit your risk of skin cancer by first limiting your exposure to the sun;
  • minimize the time you spend outdoors on sunny days, especially between 11am and 3pm;
  • if you do go out, wear long sleeves and long pants with a tight weave 
  • protect your eyes with UV-blocking sunglasses;
  • wear a wide-brimmed hat — the brim should be at least the width of the palm of your hand, and cover the full circumference of your head; and,
  • use a good layer of CDA approved sunscreen that’s at least SPF 30 or higher as your last line of defence between any exposed skin and harmful UV radiation. 
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