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About one out of every ten people has at least one unusual (or atypical) mole that looks different from an ordinary mole. The medical term for these unusual moles is dysplastic nevi.
Doctors believe that dysplastic nevi are more likely than ordinary moles to develop into a type of skin cancer called melanoma. Because of this, moles should be checked regularly by a doctor, especially if they look unusual, grow larger, or change in colour, outline, or in any other way.
These pictures will give you an idea of what to look for:
| ORDINARY MOLES | UNUSUAL MOLES | |
| Colour | Evenly tan or brown; all typical moles on one person tend to look similar. | Mixture of tan, brown, and red/pink. A person's moles often look quite different from one another. |
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| Shape | Round or oval, with a distinct edge that separates the mole from the rest of the skin. | Have irregular, sometimes notched edges. May fade into the skin around it. The flat portion of the mole may be level with the skin. |
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| Surface | Begin as flat, smooth spots on skin (1a); may become raised (1b) and form a smooth bump (1c). | May have a smooth, slightly scaly, or rough, irregular, "pebbly" appearance. |
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| Size | Usually less than 5 millimeters (about 1/4 inch) across (size of a pencil eraser). | Often larger than 5 millimeters (about 1/4 inch) across and sometimes larger than 10 millimeters (about 1/2 inch). |
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| Number | Between 10 and 40 typical moles may be present on an adult's body. | May be present in large numbers (more than 100 on the same person). However, some people have only a few dysplastic nevi. |
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| Location | Usually found above the waist on sun-exposed surfaces of the body. Scalp, breasts, and buttocks rarely have normal moles. | May occur anywhere on the body but most frequently on the back and areas exposed to the sun. May also appear below the waist and on the scalp, breasts, and buttocks. |
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- (US National Cancer Institute, November 2007)
