General Information About Melanoma

Melanoma is a disease in which malignant (cancer) cells form in the skin cells called melanocytes (cells that color the skin).

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.

The skin is the body’s largest organ. It protects against heat, sunlight, injury, and infection. The skin has 2 main layers: the epidermis (upper or outer layer) and the dermis (lower or inner layer).
When melanoma starts in the skin, the disease is called cutaneous melanoma. This PDQ summary is about cutaneous (skin) melanoma. Melanoma may also occur in the eye and is called intraocular or ocular melanoma. (See the PDQ summary on Intraocular (Eye) Melanoma Treatment for more information.)
There are 3 types of skin cancer:

• Melanoma.
• Basal cell skin cancer.
• Squamous cell skin cancer.

What is Melanoma

Melanoma is the most serious type of skin cancer. It begins in skin cells called melanocytes. Though melanoma is predominantly found on the skin, it can even occur in the eye (uveal melanoma). Melanocytes are the cells that make melanin, which gives skin its color. Melanin also protects the deeper layers of the skin from the sun's harmful ultraviolet (UV) rays. When people spend time in the sunlight, the melanocytes make more melanin and cause the skin to tan. This also happens when skin is exposed to other forms of ultraviolet light (such as in a tanning booth). If the skin receives too much ultraviolet light, the melanocytes may begin to grow abnormally and become cancerous. This condition is called melanoma.