Skin cancer is any of a number of cancers that arise from the cells of the skin. The three major types are basal-cell carcinoma, squamous cell cancer and melanoma. They are the most common form of cancer, making up about 40% of all cancers worldwide.
The vast majority of skin cancers arise from exposure to ultraviolet light, almost always from overexposure to the sun. All three types present as discolorations or deformations of the skin. Basal cell cancers form a small translucent patch. Squamous cell cancers often present similar to a scab or red crusted bump, but unlike scabs do not heal. Melanomas present as irregularly shaped dark patches on the skin, similar to moles.
Basal cell cancer is unlikely to spread and is very treatable. Squamous cell cancer is more likely to spread, but is also treatable and rarely fatal. Melanomas are the most aggressive types and frequently result in the death of the patient.