Most skin cancers are thought to be caused by excessive exposure to UV rays, including those from the sun, tanning beds, and sunlamps. This excessive exposure results in skin cell DNA damage, causing cell mutations. When DNA damage and cell mutations go unnoticed and unrepaired by the body, the cells start to reproduce out of control, causing the development of cancerous growths and tumors. Individuals may also have a genetic predisposition to developing skin cancer.