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).
The epidermis is made up of 3 kinds of cells:
- Squamous cells are the thin, flat cells that make up most of the epidermis.
- Basal cells are the round cells under the squamous cells.
- Melanocytes are found throughout the lower part of the epidermis. They 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 tan, or darken.
Anatomy of the skin, showing the epidermis, dermis, and subcutaneous tissue. Melanocytes are in the layer of basal cells at the deepest part of the epidermis.
See the following PDQ summaries for more information about skin cancer:
- Skin Cancer Screening
- Skin Cancer Treatment
- Melanoma Treatment
- Genetics of Skin Cancer
There are several types of skin cancer.
The most common types of skin cancer are squamous cell carcinoma, which forms in the squamous cells and basal cell carcinoma, which forms in the basal cells. Squamous cell carcinoma and basal cell carcinoma are also called nonmelanoma skin cancers. Melanoma, which forms in the melanocytes, is a less common type of skin cancer that grows and spreads quickly.
Skin cancer can occur anywhere on the body, but it is most common in areas exposed to sunlight, such as the face, neck, hands, and arms.
Skin cancer is the most common cancer in the United States.
Basal cell carcinoma and squamous cell carcinoma are the most common types of skin cancer in the United States. The number of new cases of nonmelanoma skin cancer appears to be increasing every year. These nonmelanoma skin cancers can usually be cured.
The number of new cases of melanoma has been increasing for at least 30 years. Melanoma is more likely to spread to nearby tissues and other parts of the body and can be harder to cure. Finding and treating melanoma skin cancer early may help prevent death from melanoma.