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Nonmelanoma skin cancer refers to cancers that form in the basal or squamous cells of the skin.

Basal cells are found at the base of the epidermis, the top layer of skin. Basal cells continually divide and rise to the skin’s surface. As they rise, they flatten and become squamous cells, which form a thick layer above the basal cells called the squamous cell layer. The squamous cells produce a protein called keratin, which gives the skin its structure and strength.

Cancers in either of these kinds of skin cells are also called carcinomas.

Basal Cell Cancer

Basal cell cancer develops in the basal cells, which are found at the base of the top layer of the skin. It is the most common type of skin cancer. While basal cell tumors can be small or large, they rarely spread to other parts of the body.

Signs include a new or growing bump that is skin colored, pink, or shiny. A growth can develop slowly or appear suddenly. Some growths have a blue or brown hue; others may appear translucent. Other signs include an open sore that won’t heal or a reddish patch of skin that does not go away. Some growths are pink with a raised border and an indentation in the center that crusts over. Shiny areas of skin that resemble white or yellow scars could also be basal cell cancer.

This form of cancer often occurs on the head and other parts of the body exposed to the sun and easily damaged by the sun’s ultraviolet rays. It’s more common in older people, although doctors are diagnosing more basal cell cancers in young women, especially those who have used tanning beds.

People at the highest risk for developing basal cell carcinoma have fair skin, red or blond hair, and green, blue, or gray eyes.

Squamous Cell Cancer

Squamous cell cancer develops in the squamous cells, the top layer of the epidermis, which continually shed as new cells are made. The second most common form of skin cancer, squamous cell carcinoma may appear as a red, scaly area of the skin, or an open sore that does not heal. Squamous cell carcinoma can also resemble a wart.

This form of skin cancer often affects the face, nose, ears, lips, scalp, back of the hands, lower legs, shoulders, and chest area.

This cancer can spread if left untreated, especially in people who have a weakened immune system, such as those who have had an organ transplant and take immunosuppressive medications. When it spreads, squamous cell cancer can be aggressive. It can invade deeper layers of skin, nerves, blood vessels, and surrounding lymph nodes, which are immune system glands that trap invaders like bacteria and viruses. About 2 percent of people with squamous cell cancer die because of it.

Risk factors include having had a blistering sunburn or frequent sun exposure as a child or as an adult, using tanning beds, and having fair skin or light green, blue, or gray eyes.

People who have a precancerous skin condition called actinic keratosis are at increased risk of developing squamous cell carcinoma.

Actinic Keratosis

Although the precancerous skin condition actinic keratosis often grows slowly, it can increase your risk of developing squamous cell carcinoma. These growths, which occur as a result of sun exposure, usually appear as small, scaly spots. Most are red, but some are tan, pink, or skin colored. They are commonly located in the same places that squamous cell cancer develops—the ears, nose, back of the hands, shoulders, and chest.