Moles are any spot or irregularity in the skin which develops from overgrowth of melanocytes. Melanocytes are pigment producing cells of the skin. A mole is also called a nevus. Moles are very common and are usually round or oval in shape. They may be present at birth (congenital mole) or may appear later (acquired mole). Another type of mole is an atypical mole or dysplastic mole which is usually larger, irregularly shaped and may be of uneven color. Atypical moles have a greater tendency to develop into a serious type of skin cancer called melanoma.