Home > About Melanoma: How Does It Start?
Mucous membranes
Remote internal site
Clear skin*
Pre-existing moles
Age spots (liver spots)**
*Includes under toenails and fingernails
**Usually occurs in people in their 70s or older


The first step in learning about melanoma is to learn about moles, common pigmented skin lesions that can be flat or raised. There are two types of moles: ordinary and atypical (the medical term for atypical moles is dysplastic nevi). 10 to 15 percent of the white population have atypical moles. Examples of both types are shown below. Characteristics of each type are summarized in the table beneath the photos.

Examples of Ordinary & Atypical Moles

A flat ordinary mole
A raised ordinary mole
A flat atypical mole
A raised atypical mole

Characteristics of Ordinary & Atypical Moles


Round or oval shape


Sharp, even borders with skin


Uniform color (usually brown)


Less than 1/4 inch wide


Cauliflower or smooth surface


Even dome shape if mole is raised


Irregular shape


Uneven and/or fuzzy borders with skin


Two or more shades of brown or pink


1/4 inch wide or more


Cauliflower or smooth surface

Flat edges with "fried egg" center if
mole is raised

How Likely is a Mole to Develop into a Melanoma?

  • The chance of melanoma developing from an ordinary mole is less than one in 3,000.
  • The chance of melanoma developing from an atypical mole is about one in 100.
  • Melanoma is much more likely to develop from a flat or slightly raised pre-existing mole than from a fully raised pre-existing mole.
  • A mole with hair growing from it is no more likely to develop melanoma than a similar mole without hair.