July is here, and summer is getting into full swing. As you heads out to geocache or even just to hit the beaches, remember to protect your skin from the sun’s rays. Energy from the sun sustains all life on earth. However, some forms of sun energy can be harmful to life.

Our sun radiates many types of radiation besides that which we can see. At the low end of the spectrum is the infrared (IR) and at the high end ultraviolet (UV). The visible light spectrum is sandwiched in the middle. There are three type of UV radiation, aptly named UVA, UVB and UVC.

Fortunately, our planet has a protective shield in the atmosphere called the Ozone layer which provides partial protection from these damaging types of radiation. Without this protection, much of the life on the Earth could not survive. UVA, which has the longest wavelength, passes right through the ozone layer and is not blocked. UVB is partially blocked so only a percentage of UVB radiation reaches the surface. UVC has a shorter wavelength than UVA and UVB and is completely blocked from reaching the surface. Therefore our concern is with UVA and UVB, which easily penetrate into our skin and eyes.

Too much exposure to UV radiation can cause serious health problems such as skin cancer, cataracts and immune suppression.

UVA radiation is the least energetic form; however it penetrates deeply into our skin and causes premature aging and wrinkles. Up to 90% of visible skin changes attributed to aging are due to sun exposure.

UVB radiation mostly impacts the surface of the skin and is primarily responsible for sunburn. An easy way to remember this is UVA – A for Aging and UVB – B for Burning.

In the United States, the National Weather Service (NWS) calculates the UV index so that the public can schedule outdoor activities to avoid dangerous overexposure to the sun. The UV index assigns a number the next day’s likely UV radiation levels and categorizes the level of exposure risk for people who plan to be outdoors.

The UV index for the United States can be found on the SunWise Web site and it is zip code searchable to provide the UV index for your local area.

Did you know that Canada developed the UV index? In 1992, Canada became the first country in the world to issue nationwide daily UV forecasts. In Canada the UV index can be found here.

In the UK the UV index can be found here.

The remainder of Europe can be found here.

The amount of UV you receive depends on these factors:

• 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 spring and summer (April to August), less in fall and least in the winter. It is the opposite if you are in the Southern hemisphere.
• How long you're out in the sun. The longer you are out in the sun, the more UV you receive.
• Cloud Cover. A thick, heavy layer of cloud blocks UV. However, puffy, fair-weather clouds or layers of thin, light cloud let most of it through. So the darker the clouds, the less the UV. Be careful under thin clouds - the sun's rays may not feel 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 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. UV increases 2% for every 1000 feet increase in elevation.
• vWhere you are on the earth's surface. UV is strongest at the equator and gets weaker as you go toward the poles. The poles receive the least UV. If you live in the Southern United States, you will receive more UV than if you live in the Canada.
• The state of the ozone layer. The amount of ozone in the stratosphere (the ozone layer) varies from day to day: the more ozone, the less UV. Ozone depletion may also increase UV levels. The value of the UV Index reflects the state of the ozone layer.
• What you're wearing. Summer clothes generally expose more skin to UV.

The sun delivers the most UV when it is high overhead at midday in the spring or summer. A good rule of thumb is that if your shadow is shorter than you are, you must 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. UV rays can burn even if it's cold!

ACTION STEPS FOR SUN PROTECTION

• Limit Time in the Midday Sun. The sun’s rays are strongest between 10 am and 4 pm. Whenever possible, limit exposure to the sun during these hours.
• Seek Shade. Staying under cover is one of the best ways to protect yourself from the sun. Remember the shadow rule: “Watch your shadow – no shadow, seek shade!”
• Always Use Sunscreen. A broad spectrum sunscreen with a Sun Protection Factor (SPF) of at least 15 blocks most UV radiation. Apply sunscreen liberally on exposed skin and reapply every two hours. Even waterproof sunscreen can come off when you towel off sweat or water.
• Wear a Hat. A hat with a wide brim offers good sun protection for your eyes, ears, face and the back of your neck – areas particularly prone to overexposure to the sun.
• Cover Up. Wearing tightly woven, loose-fitting, and full-length clothing is a good way to protect your skin from the sun’s UV rays.
• Wear Sunglasses That Block 99 to 100 Percent of UV Radiation. This will greatly reduce sun exposure that can lead to cataracts and other eye damage. Check the label when buying sunglasses.
• Watch for the UV Index. The UV Index provides important information to help you plan your outdoor activities in ways that prevent overexposure to the sun.

Next Month: UV Radiation and Your Health