Test Your Risk From UV Radiation

Information on UV Radiation

UV Radiation

Ultraviolet radiation (or UV) is electromagetic energy with wavelengths between .2 and .4 microns. (Need a quick review of radiation) The sun emits UV radiation as well as radiant energy at other wavelenghts, such as the visible. UV light has more energy than the visible light emitted by the sun. UV radiation has been classified as three bands or types, based on on the wavelenght:
  • UV-A (.32 to .4 microns): The amount of UV radiation at the surface remains fairly constant throughout the year. These rays contribute to premature aging of the skin.
  • UV-B (.28 to .32 microns): These rays, which are more intense then UV-A radiation, are more intense in the summer than winter, increase towards the equator and at higher altitudes. Absorption of UV-B by your skin is the common cause of sun burn.
  • UV-C (.2 to .28 microns): The most intense and dangerouse UV radiation. It is normally absorbed completely by the ozone layer and does not reach the surface.

    Your skin and UV Radiation

    Exposing your skin to ultraviolet radiation stimulates melanin-producing cells. With increasing amounts of melanin you skin darkens. This tanning provides a protection against UV radiation damage. Prolonged exposure to UV radiation causes the skin to loss its resiliency and over time your skin will begin to look like leather. UV radiation can also activate a cancerous transformation of skin cells.

    Basic forms of Skin Cancer

    Basal Cell Carcinomas begins as small shiny bumps and grows slowly. It is the most common form of skin cancer.

    Squamous Cell Carcinoms is another common form of skin cancer. When these tumors first appear they are firm to the touch. They, like the basal cell carcinomas, appear most often on sun-exposed areas of your body.

    Malignant Melanoma is the most dangerous form of skin cancer. Malignant melanoma, like basal and squamous carcinomas, is linked to overexposure to the sun; however, it can appear any place on your body. When detected early and with proper treatment, the recovery rate from this form of skin cancer can be very high.

    - Advanced stage.

    Actinitic keratosis is a precancerous skin condition. They are small scaly spots commonly found on the face and back of the hands of fair-skinned people who have had significant exposure to the sun.

    You can protect you skin to over exposure by wearing proper clothing and/or sunscreen. Sunscreen with a Sun Protection Factor (SPF) of 15 blocks out most of the harmful UV radiation. A sunscreen with an SPF 15 means that you can stay out in the sun 15 times longer than you can with no protection before you skin begins to turn pink.

    Your eyes and UV Radiation

    Your eyes are also sensitive to overexposure of UV radiation. UV-B is partly absorbed by the cornea. UV-A passes through the cornea and with time and overexposure may contribute to the formation of cataracts. Snow reflects up to 85% of the incident UV radiation. This additional amount of absorption of reflected UV-B radiation by the cornea can result in snow blindness -- a sun burning of the eye. Sunglasses screenout 99% of the UV-A and UV-B radiation reaching your eyes.

    UV - its not all bad

    Fortunately, if detected early, the cancers listed above can be treated. DO NOT PANIC. Sunshine is also good for us! It makes us cheery. UV radiation plays a role in the our body's production of vitamin K. A lack of Vitamin K can lead to liver damage and jaundice. Green leafy vegetables are one common source of vitamin K. So your parents were right -"Eat your vegetables." Speaking of plants, UV radiation is important in pollination of certain plants. Some insects, such as honeybees, find reflected UV light by some plants alluring. Some spiders take advantage of the alluring nature of reflected UV radiation to some insects by including strands in their web that are UV reflective, and thus also alluring.

    Your risk of skin cancer is related to the amount of time you spend in the sun and your skin type. By answering a few simple questions you can estimate your sensitivity to UV exposure. Before taking the test, there are some facts that you should know.

    The amount of UV radiation that you are exposed to depends on

  • How high the sun is in the sky. This is a function of
    Season - Greatest exposure of UV light in the summer.
    Latitude - Strongest UV concentration in tropical locations near the equator.
    Time of Day - Most intense UV radiation occurs between 10 a.m. and 2 p.m.
  • Cloud Cover - Through absorption and reflection, clouds reduce the amount of UV radiation at the surface.
  • Altitude: UV concentrations increase the higher the altitude.
  • Surface: The surface can reflect solar energy back toward you. Snow reflects up to 85% of the incident UV rays, sand and concrete up to 12%, grass and water 5%.

    UV-Skin Sensitivity Test

    This test is qualitative in nature. You are well aware of how easily you sunburn and you should take appropriate actions. If you have problems you should see your medical doctor or a dermatologist.

    UV Index

    The UV Index is a forecast of the expected risk of overexposure to the sun. It was developed by the National Weather Service and the Envrionmental Protection Agency. Based on a scale from 0-10, it indicates the degree of caution you should take when outdoors. A 10 indicates a high risk of overexposure to UV radiation. The forcast of the UV Index takes into account, latitude, altitude, weather conditions, time of year and ozone concentrations.

  • Recent map of the UV-Index over the US. (May not be available.)
  • Return to WxWise page

    The skin cancer images were obtained from a pamplet distributed by the American Academy of Dermaology. For more information, their address is: American Academy of Dermatology, 930 North Meacham Road, P.O. Box 4014 Schaumburg, IL 60168-4014.

    Please refer questions to Dr. Steve Ackerman/stevea@ssec.wisc.edu