Mayo Clinic cites ultraviolet light from both the sun and tanning beds as the most common cause of skin cancer. Other potential causes that do not involve sunlight are fair skin, excessive moles, living at a high altitude and a family history of skin cancer. The disease can also be caused by exposure to radiation, arsenic or tar according to the American Academy of Dermatology.
Skin cancer begins in the epidermis, according to Mayo Clinic, usually on areas that had sun exposure. Too much exposure to the sun risks eventual skin cancer as does multiple sunburns as a child. People with fair skin and blue, green or gray eyes are at higher risk for skin cancer because melanin limits damage from ultraviolet radiation. According to the American Academy of Dermatology, people with more than 50 moles are at higher risk for skin cancer, including those with atypical or dysplastic nevi. The moles can develop into skin cancer, so they should be monitored for changes in size and shape. Anyone who has a blood relative who had cancer is at higher risk, and those who have had skin cancer once are at risk to get it again. Treatments that include radiation or consuming or working with arsenic increase skin cancer risk. Immune systems weakened by medication from organ transplants, HIV or AIDS can also lead to skin cancer, according to Mayo Clinic.