There are multiple types of nevi. A dysplastic (or "atypical") nevus is a large, irregularly-shaped type that particularly increases a person's risk of melanoma: About 50% of melanoma cases occur in people who have dysplastic nevi. People with this condition should have a thorough skin exam by a dermatologist every six months. Moles usually appear late in childhood, but some are present at birth in those with a condition called "congenital melanocytic nevi." The lifetime risk of getting melanoma for people with congenital melanocytic nevi has been estimated to be up to 10%, depending on the size of the nevus.