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. The "Pictures of Ordinary Moles and Dysplastic Nevi ¹" section shows the differences between ordinary moles and 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 or nurse specialist, especially if they look unusual; grow larger; or change in color, outline, or in any other way.