Nevus, also known as a
mole, is the medical term for sharply circumscribed and
chronic lesions of the
skin or
mucosa. These lesions are commonly named
birthmarks or
beauty marks. Nevi are
benign by definition. However, 25% of malignant melanomas (a skin cancer) arise from pre-existing nevi. Using the term nevus and nevi loosely, most physicians and dermatologists are actually referring to a variant of nevus called the "
melanocytic nevus", which are composed of
melanocytes. Histologically, melanocytic nevi are distinguished from
lentigines (also a type of benign pigmented
macule) by the presence of nests of melanocytes, which lentigines (plural form of lentigo) lack.