Ultraviolet (UV) radiation from the sun is the main cause of skin cancer. Energy from the sun actually is a form of radiation. It consists of visible light and other rays that people can't see. Invisible infrared radiation, for instance, makes sunlight feel hot. UV also is invisible, and causes sunburn and sun tan.
UV rays damage DNA, the genetic material that makes up genes. Genes control the growth and overall health of skin cells. If the genetic damage is severe, a normal skin cell may begin to grow in the uncontrolled, disorderly way of cancer cells. UV also can cause sunburn, and other damage that makes the skin look prematurely old and wrinkled.
Two kinds of rays exist in 
- Ultraviolet A (UVA)
- Ultraviolet B (UVB)
Scientists once thought that excessive exposure to UVB rays was the main cause of skin cancer. Now they think that UVA also is involved. That's why it is important to use a sunscreen product that protects against both UVA and UVB rays.
Some cases of skin cancer, however, may be hereditary and run in families. In those cases, skin cancer is caused by abnormal genes that children inherit from their parents. Genes make parents and children look somewhat alike. They also make them likely to get some of the same diseases.
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