Skin cancer is the most common form of human cancer, with over 1 million new cases occurring annually. It is caused by UV rays from the sun and tanning beds, with excessive and unprotected exposure increasing risk. The three main types are basal cell carcinoma, squamous cell carcinoma, and melanoma, ordered from least to most dangerous. Signs include changes in the skin like growths, sores, or changes to existing marks. Prevention focuses on avoiding UV exposure and using sunscreen while treatment depends on the type and may include surgery, radiation, or cryosurgery.