Any change in an existing wart, mole or other skin lesion, or the development of a new growth that ulcerates and does not heal well, could indicate skin cancer. Skin cancer has a high cure rate if it is treated early, but neglect can allow the cancer to spread, causing disability or death.

Over 90% of skin cancers occur on areas of the skin that are regularly exposed to sunlight or other ultraviolet radiation. This is considered the primary cause of all skin cancers.

Other risks include genetic predisposition (skin cancers are more common in those who have light colored skin, blue or green eyes, and blond or red hair), chemical pollution, and overexposure to X-rays or other forms of radiation. Exposure to arsenic, which may be present in some herbicides, is another risk for development of skin cancers.

Squamous cell cancer is a malignant tumor. It is more aggressive than basal cell cancer, but still may be relatively slow-growing. It is more likely than basal cell cancer to spread (metastasize) to other locations, including internal organs. The incidence of skin cancer has increased greatly. In 1990, 600,000 Americans were diagnosed with either basal cell cancer or squamous cell cancer, up from 400,000 in 1980.

Squamous cell cancer involves cancerous changes to the cells of the middle portion of the epidermal skin layer. It is usually painless initially, but may become painful with the development of ulcers that do not heal. This cancer may begin in normal skin; in the skin of a burn, injury or scar; or at a site of chronic inflammation (which may occur with many skin disorders). It most often originates from sun-damaged skin areas, such as actinic keratosis. It usually begins after age 50.