Skin cancer refers to a group of cancers that originate in the skin. It is the most common type of cancer and affects millions of people worldwide each year. There are three main types of skin cancer - basal cell carcinoma, squamous cell carcinoma, and melanoma. Basal cell carcinoma is the most common form and usually appears on sun-exposed areas such as the face, neck or hands. Squamous cell carcinoma is less common but can be more aggressive if not treated early. Melanoma is the rarest but most dangerous type of skin cancer, and it occurs when pigment-producing cells in the skin become malignant. Early detection and treatment are crucial to prevent serious complications or spread of the disease.