UV - The ABCs Energy from the sun sustains all life on earth. However, some forms of sun energy can be harmful to life. This includes the sun's burning or "ultraviolet" rays - the rays that cause sunburn and skin cancer. We can't see ultraviolet or "UV" rays, as this form of sun energy is invisible. There are three types of ultraviolet: UV-A, UV-B and UV-C. UV-A is the weakest form. It causes skin aging, wrinkles and can also damage outdoor plastics and paint. UV-B, which is stronger than UV-A, is the most harmful to us and other life forms. UV-B causes skin cancer and cataracts - a permanent clouding of the eye which reduces vision. Both UV-B and UV-A cause suntans and sunburns. UV-B also reduces the growth of plants, and may affect the health of wildlife and other animals. UV-C, which is even stronger than UV-B, never reaches the earth's surface because it is filtered out by the atmosphere . Fortunately, there are simple ways to protect yourself from UV-B. Action you take to protect yourself from UV-B will also safeguard against UV-A (except for certain sunscreens).

UV and the Ozone Layer

UV-B is a natural part of the sun's rays - it has always been with us. We should have always been careful about spending too much time in the sun, even before we heard about the thinning of the earth's ozone layer.

Most of the UV-B rays from the sun are screened out by the ozone layer - a thin veil of gas high in the atmosphere. This invisible shield acts as our planet's sun-screen.

In the past few years, the ozone layer has become slightly thinner than it used to be. This means slightly more of the sun's UV-B rays can now reach the earth's surface.

Throughout Canada, there has been a small loss of ozone during late winter over the last ten years. UV-B is naturally weaker during this time and, even with a small loss of ozone, it is still not as strong as what we would normally get on a typical summer day.

How much UV reaches me?

You get more UV, and sunburn faster, when the sun's rays are stronger. The amount of UV depends on:

• The time of day. UV is greatest at midday (when the sun is highest in the sky), and less in early morning or late afternoon.
• The season. UV is greatest in the summer (May to August), less in spring and fall, and least in the winter.
• Cloud Cover. A thick, heavy layer of cloud blocks UV. Puffy, fair-weather clouds or layers of thin, light cloud let most of it through. The darker the clouds, the less the UV. Be careful under thin clouds - the sun's rays don't feel as hot, but they can still burn. And watch out for haze, because it does not block UV.
• The type of surface you are on. You get much more UV on snow, sand, water or concrete, since these surfaces reflect the sun's rays back onto your skin, just like a mirror. The brighter the surface, the more UV is reflected - fresh snow and dry sand reflect the most.
• Your elevation. You get more UV on a mountain than at lower elevations, as the air is clearer and thinner.
• Where you are on the earth's surface. UV is strongest at the equator, and gets weaker as you go towards the earth's poles. The poles receive the least UV. If you live in southern Canada, you will receive more UV than if you live in the Arctic.
• How long you're out in the sun. The longer you are out in the sun, the more UV you receive.
• What you're wearing. Summer clothes often expose more skin to UV.
  

The sun delivers the most UV when it is high overhead at midday in the summertime. A good rule of thumb is: "if your shadow is shorter than you are, you should protect yourself from the sun."

Don't confuse temperature and UV. Light cloud, or a breeze, can make you feel cooler - but they don't reduce the UV.

Be extra careful

• in summer
• in the middle of the day
• at the beach
• on the ski slopes

Be especially careful on your holidays! Winter sun vacations in the Caribbean, Mexico and Hawaii bring you closer to the equator, where UV is stronger. Here, you'll likely wear fewer clothes and visit the beach where UV reflects off the sand.

Skiing and other outdoor winter fun can also increase your exposure to UV. Snow reflects UV, and, if you are skiing in the mountains, you will receive more UV due to the elevation.

How can I protect myself?

You can still enjoy the great outdoors - just remember to take a few simple precautions, especially if you work or play outside, especially at the beach or on snow.

Try to spend less time in the sun. When you are outdoors, wear clothes that cover your skin such as hats, shoes, long pants and long-sleeved shirts. Protect your eyes with sunglasses that are UV-rated. Wear sunscreen on skin that is not covered, especially if you are light-skinned. Your sunscreen should block both UV-B and UV-A and have a SPF (Sun Protection Factor) of 15 or more.

If you are wearing fewer clothes or swimming, limit the time you spend in the sun by sitting in the shade. Be sure to use sunscreen, and reapply it every two hours, or after swimming or exercising.

If you have more questions about your health, ask your your doctor or public health nurse. By following these simple rules, you won't have to worry about UV.

How can I protect myself from UV?

• spend less time in the sun
• cover up - wear a hat, long-sleeved shirt and long pants
• wear sunglasses
• wear sunscreen

In 1992 Environment Canada scientists developed a method to predict the strength of the sun's UV rays, based on day-to-day changes in the ozone layer. That same year, Canada developed the UV Index and became the first country in the world to issue nation-wide daily forecasts of tomorrow's UV. Watch for Environment Canada's UV Index in your daily weather forecast - listen for it on radio or TV, check the newspaper, or contact your local weather office.

The UV Index is produced for locations across Canada, as well as holiday destinations. The Index will change slightly with day-to-day changes in the ozone layer. Much larger variations can be seen as UV changes with the seasons, the time of day and the amount of cloud cover.

UV is measured on a scale of 0 to 10, with 10 being a typical midday value for a summer day in the tropics - where UV is at its highest on earth. The higher the number on the UV index, the more UV you will get, and the faster you'll sunburn.

What does the UV Index mean to me?

UV Index	Category	Sunburn Time
over 9	extreme	less than 15 minutes
7-9	high	about 20 minutes
4-7	medium	about 30 minutes
0-4	low	more than 1 hour
When the UV index is over 9, UV-B is extremely strong, and you will burn in less than 15 minutes. (Sunburn times are for light untanned skin, the times would be somewhat longer for those with darker skin.) Even if you do not get a burn, you may still be damaging your skin.

The UV Index: Typical summer midday values

	UV Index
Tropics	10 (extreme)
Washington, D.C.	8.8 (high)
Toronto	8.0 (high)
Halifax	7.5 (high)
Edmonton	7.0 (high)
Yellowknife	6.0 (moderate)
Iqaluit, NWT	4.8 (moderate)
North Pole	2.3 (low)
The farther south you go, the higher the UV index. This is why you burn so quickly on a southern vacation.

Watch for Environment Canada's UV Index and be extra careful on sunny days when the UV index is high.