What is ultraviolet (UV) radiation?

From http://www.cancer.org

Ultraviolet (UV) radiation is thought to be the major risk factor for most skin cancers. Sunlight is the main source of UV rays, which can damage the genes in your skin cells. Tanning lamps and beds are also sources of UV radiation. People with high levels of exposure to light from these sources are at greater risk for skin cancer.

Ultraviolet radiation has 3 wavelength ranges:

  • UVA rays cause cells to age and can cause some damage to cells’ DNA. They are linked to long-term skin damage such as wrinkles, but are also thought to play a role in some skin cancers.
  • UVB rays can cause direct damage to the DNA, and are the main rays that cause sunburns. They are also thought to cause most skin cancers.
  • UVC rays don’t get through our atmosphere and therefore are not present in sunlight. They are not normally a cause of skin cancer.

UVA and UVB rays make up only a very small portion of the sun’s wavelengths, but they are the main cause of the damaging effects of the sun on the skin. UV radiation damages the DNA of skin cells. Skin cancers begin when this damage affects the DNA of genes that control skin cell growth. Both UVA and UVB rays damage skin and cause skin cancer. UVB rays are a more potent cause of at least some skin cancers, but based on current knowledge, there are no safe UV rays.

The amount of UV exposure depends on the strength of the rays, the length of time the skin is exposed, and whether the skin is protected with clothing or sunscreen.

Skin cancers are one result of getting too much sun, but there are other effects as well. The short-term results of unprotected exposure to UV rays are sunburn and tanning, which are signs of skin damage. Long-term exposure can cause prematurely aged skin, wrinkles, loss of skin elasticity, dark patches (lentigos, sometimes called age spots or liver spots), and pre-cancerous skin changes (such as dry, scaly, rough patches called actinic keratoses).

The sun’s UV rays also increase a person’s risk of cataracts and certain other eye problems and can suppress the skin’s immune system. Dark-skinned people are generally less likely to get skin cancer than light-skinned people, but they can still get cataracts and suppression of the skin’s immune system.

The UV Index

The amount of UV light reaching the ground in any given place depends on a number of factors, including the time of day, time of year, elevation, and cloud cover. To help people better understand the intensity of UV light in their area on a given day, the Environmental Protection Agency (EPA) and the National Weather Service have developed the UV Index. The UV Index number, on a scale from 1 to 11+, is a measure of the amount of UV radiation reaching the earth’s surface during an hour around noon. The higher the number, the greater the exposure to UV rays.

The UV Index is given daily for regions throughout the country. Many newspaper, television, and online weather forecasts include the projected UV Index for the following day. Further information about the UV Index, as well as your local UV Index forecast, is available on the EPA’s web site at www.epa.gov/sunwise/uvindex.html. As with any forecast, local changes in cloud cover and other factors may change the actual UV levels experienced.


Leave a Reply