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:
Found in the lower part of the epidermis, these cells make melanin, the pigment that gives skin its natural color. When skin is exposed to the sun, melanocytes make more pigment, causing the skin to darken.
Skin cancer can occur anywhere on the body, but it is most common in skin that has been exposed to sunlight, such as the face, neck, hands, and arms. There are several 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. Actinic keratosis is a skin condition that sometimes develops into squamous cell carcinoma.
This summary refers to the treatment of nonmelanoma skin cancer and actinic keratosis. Nonmelanoma skin cancers rarely spread to other parts of the body. Melanoma, the rarest form of skin cancer, is more likely to invade nearby tissues and spread to other parts of the body. Refer to the following PDQ summaries for information on melanoma and other kinds of skin cancer: Melanoma Treatment, Risk Factors and Tests
For more information on skin cancer and its treatment, visit the National Cancer Institute