The role of UV light Much of the damage to DNA in skin cells results from ultraviolet (UV) radiation found in sunlight and in commercial tanning lamps and tanning beds. UV light is divided into three wavelength bands: ultraviolet A (UVA), ultraviolet B (UVB) and ultraviolet C (UVC). Only UVA and UVB rays reach the earth. UVC radiation is completely absorbed by atmospheric ozone.
At one time scientists believed that only UVB rays played a role in the formation of skin cancer. And UVB light does cause harmful changes in skin cell DNA, including the development of oncogenes — a type of gene that can turn a normal cell into a malignant one. UVB rays are responsible for sunburn and for many basal cell and squamous cell cancers. But UVA also contributes to skin cancer. It penetrates the skin more deeply than UVB does, weakens the skin's immune system and increases the risk of cancer, especially melanoma.
Tanning beds deliver high doses of UVA, which makes them especially dangerous. What's more, occasional exposure to intense UVA puts you at greater risk of skin cancer than spending long hours in the sun does. An initial high dose of UV radiation will severely damage melanocytes, but not destroy them. When these damaged cells are subjected to further intense bouts of UVA light, they have little capacity to repair their DNA. This makes them more likely to become malignant.
