Skin cancer is a disease in which malignant (cancer) cells form in the tissues of the skin.
The skin is the body's largest organ. It protects against heat, sunlight, injury, and infection. Skin also helps control body temperature and stores water, fat, and vitamin D. The skin has several layers, but the two main layers are the epidermis (upper or outer layer) and the dermis (lower or inner layer). Skin cancer begins in the epidermis, which is made up of three kinds of cells:
- Squamous cells: Thin, flat cells that form the top layer of the epidermis.
- Basal cells: Round cells under the squamous cells.
- Melanocytes: Cells that make melanin and are found in the lower part of the epidermis. Melanin is the pigment that gives skin its natural color. When skin is exposed to the sun, melanocytes make more pigment and cause the skin to darken.
Anatomy of the skin, showing the epidermis, dermis, and subcutaneous tissue.
Skin cancer can occur anywhere on the body, but it is most common in skin that is often exposed to sunlight, such as the face, neck, hands, and arms.
There are different types of cancer that start in the skin.
The most common types are basal cell carcinoma and squamous cell carcinoma, which are nonmelanoma skin cancers. Nonmelanoma skin cancers rarely spread to other parts of the body. Melanoma is the rarest form of skin cancer. It is more likely to invade nearby tissues and spread to other parts of the body. Actinic keratosis is a skin condition that sometimes becomes squamous cell carcinoma.
This summary is about nonmelanoma skin cancer and actinic keratosis. See the following PDQ summaries for information on melanoma and other kinds of cancer that affect the skin:
Skin color and being exposed to sunlight can increase the risk of nonmelanoma skin cancer and actinic keratosis.
Anything that increases your chance of getting a disease is called a risk factor. Having a risk factor does not mean that you will get cancer; not having risk factors doesn't mean that you will not get cancer. Talk with your doctor if you think you may be at risk. Risk factors for basal cell carcinoma and squamous cell carcinoma include the following:
- Being exposed to natural sunlight or artificial sunlight (such as from tanning beds) over long periods of time.
- Having a fair complexion, which includes the following:
- Fair skin that freckles and burns easily, does not tan, or tans poorly.
- Blue or green or other light-colored eyes.
- Red or blond hair.
- Having actinic keratosis.
- Past treatment with radiation.
- Having a weakened immune system.
- Having certain changes in the genes that are linked to skin cancer.
- Being exposed to arsenic.