Squamous cell skin cancer is a type of tumor that affects the skin.

Squamous cell cancer occurs when cells in the skin start to change. The changes may begin in normal skin or in skin that has been injured or inflamed. Most skin cancers occur on skin that is regularly exposed to sunlight or other ultraviolet radiation. Skin cancer is most often seen in people over age 50.

Squamous cell carcinoma in situ (also called Bowen's disease) is the earliest form of squamous cell cancer. The cancer has not yet invaded surrounding tissue. It appears as large reddish patches (often larger than 1 inch) that are scaly and crusted.

Actinic keratosis is a precancerous skin lesion. In rare cases it may become a squamous cell cancer.

Risks for squamous cell skin cancer include:

• Having light-colored skin, blue or green eyes, or blond or red hair
• Long-term, daily sun exposure (such as in people who work outside)
• Many severe sunburns early in life
• Older age
• A large number of x-rays
• Arsenic
• Chemical exposure

Squamous cell cancer spreads faster than basal cell cancer, but still may be relatively slow-growing. Rarely, it can spread (metastasize) to other locations, including internal organs.