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Skin Cancer
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Ultraviolet
Radiation
What
is ultraviolet radiation?
Energy from the sun reaches the earth as visible, infrared, and
ultraviolet (UV) rays.
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Ultraviolet
A (UVA) is made up of wavelengths 320 to 400 nanometers (nm) in
length.
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Ultraviolet
B (UVB) wavelengths are 280 to 320 nm in length.
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Ultraviolet
C (UVC) wavelengths are 100 to 280 nm in length.
Only UVA and
UVB ultraviolet rays reach the earth's surface. The earth's atmosphere
absorbs UVC wavelengths.
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UVB
rays cause a much greater risk of skin cancer than UVA. However,
UVA rays cause aging, wrinkling, and loss of elasticity.
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UVA
also increases the damaging effects of UVB, including skin cancer and
cataracts (an eye disorder
characterized by a change in the structure of the crystalline lens
that causes blurred vision).
In most cases, ultraviolet rays react with a chemical called melanin, that
is found in the skin. This is the first defense against the sun, as it is the
melanin that absorbs the dangerous UV rays that can do serious skin
damage. A sunburn develops when the amount of UV damage exceeds the
protection that the skin’s melanin can provide. While a small amount of
exposure to sunlight is healthy and pleasurable, too much can be
dangerous. Measures should be taken to prevent overexposure to sunlight in
order to reduce the risks of cancers, premature aging of the skin, the
development of cataracts, and other harmful effects.
What is the Ultraviolet (UV)
Index?
In response to the increasing incidence of
skin cancer, cataracts, and other effects from exposure to the sun's
harmful rays, the National Weather Service (NWS), the US Environmental
Protection Agency (EPA), and the Centers for Disease Control and
Prevention (CDC) collaborated on a sun-awareness information program.
An important part of this program is the Ultraviolet (UV) Index,
developed by the National Meteorological Center of the National Weather
Service.
The Index is a next-day
forecast that estimates the amount of ultraviolet radiation that will
reach the earth's surface - providing important information to help you
prevent overexposure to the sun's rays. The Index also includes the
effects of cloud cover on the anticipated UV exposure level for the next
day.
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This content was last reviewed by a University of Maryland Medicine expert on
May 16, 2003
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