Skin cancer is the most common cancer in the United States. The skin protects against heat, sunlight, injury, and infection. Skin also helps control body temperature and stores water and fat. Most cases of melanoma, the deadliest kind of skin cancer, are caused by exposure to ultraviolet (UV) rays. Melanoma is a kind of skin cancer. It isn’t as common as other types of skin cancer, but it is the most serious. Melanoma can affect your skin only, or it may spread to your organs and bones. As with other cancers, treatment for melanoma works best when the cancer is found early.