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).
There are 3 types of skin cancer:
When melanoma starts in the skin, the disease is called cutaneous melanoma. Melanoma may also occur in mucous membranes (thin, moist layers of tissue that cover surfaces such as the lips). This PDQ summary is about cutaneous (skin) melanoma and melanoma that affects the mucous membranes. When melanoma occurs in the eye, it is called intraocular or ocular melanoma. (See the PDQ summary on Intraocular (Eye) Melanoma Treatment for more information.)
Melanoma is more aggressive than basal cell skin cancer or squamous cell skin cancer. (See the PDQ summary on Skin Cancer Treatment for more information on basal cell and squamous cell skin cancer.)
Melanoma can occur anywhere on the body.
In men, melanoma is often found on the trunk (the area from the shoulders to the hips) or the head and neck. In women, melanoma forms most often on the arms and legs. Melanoma is most common in adults, but it is sometimes found in children and adolescents. (See the PDQ summary on Unusual Cancers of Childhood for more information on melanoma in children and adolescents.)
Unusual moles, exposure to sunlight, and health history can affect the risk of melanoma.
Anything that increases your risk 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 melanoma include the following:
- 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.
- Being exposed to natural sunlight or artificial sunlight (such as from tanning beds) over long periods of time.
- Being exposed to certain factors in the environment (in the air, your home or workplace, and your food and water). Some of the environmental risk factors for melanoma are radiation, solvents, vinyl chloride, and PCBs.
- Having a history of many blistering sunburns, especially as a child or teenager.
- Having several large or many small moles.
- Having a family history of unusual moles (atypical nevus syndrome).
- Having a family or personal history of melanoma.
- Being white.
- Having a weakened immune system.
- Having certain changes in the genes that are linked to melanoma.