What Is Melanoma?

Melanoma is a type of skin cancer that begins in the melanocytes, which are the cells that give skin its color. Melanoma is less common than other skin cancers, but it is the deadliest form of skin cancer.

Melanoma can occur anywhere on the body. Melanoma in women typically develops on the arms and lower legs. Men most often develop melanoma on the area between their hips and shoulders (the "trunk"). Melanoma can also develop in the eyes, fingernails or toenails and inside the nose. It is also possible for melanoma to develop on areas of the body that are rarely exposed to the sun.


Moles, or pigmented nevi, are clusters of pigmented cells that are often dark brown or black. Moles can be present at birth (congenital pigmented nevi) or be acquired beginning in infancy. Most moles are harmless and vary in shape and size, and some may even change shape and size without becoming cancerous.

Moles that become painful, itch, bleed, suddenly become asymmetrical, or change size, shape or color should be looked at by a dermatologist. Moles are more likely to become cancerous if they are large, atypical or if the patient has a lot of moles. Melanomas often begin at a site without a known previous mole.

The ABCDE skin guide can help you identify cancerous moles. Talk to your dermatologist if you have any concerns about your moles.

  • A = Asymmetrical shape.
  • B = Border: Moles with borders that are not smooth are more likely to be cancerous.
  • C = Color: Look for moles with uneven color or changes in color.
  • D = Diameter: Most cancerous moles are larger than ¼ inch (the size of a pencil eraser), although not all large moles are cancerous.
  • E = Evolving: Look for moles that change in size or color, or become itchy and painful.