Excessive exposure to sunlight is the main cause of skin cancer. Sunlight
contains ultraviolet (UV) rays that can alter the genetic material in skin
cells, causing mutations. Sunlamps, tanning booths, and X-rays also generate UV
rays that can damage skin and cause malignant cell mutations. Basal cell
carcinoma and squamous cell carcinoma have been linked to chronic
sun exposure, typically in fair-skinned people who work outside.
Melanoma is associated with infrequent but excessive sunbathing that
causes scorching sunburn. One blistering sunburn during childhood appears to
double a person's risk for developing melanoma later in life.
Read more about the basics of skin cancer.