Overview of Congenital Moles

Congenital nevi appear on approximately 1% of newborns. A congenital nevus (plural is nevi) is a mole that is present at or develops shortly after birth. A distinction is made between small and giant nevi.

Traditionally, a giant congenital nevus is greater than 20 centimeters (cm) in diameter, while a small nevus is less than 1.5 cm. A more practical classification has been suggested, depending on the ease of surgical removal and the anatomic location of the mole. For example, a nevus that cannot be easily stitched and may require a graft after removal is considered large. Similarly, a nevus that occupies a significant proportion of one anatomic area, such as the neck or an extremity, would be considered large. On the other hand, a nevus that can be removed relatively simply or that occupies a minor portion of an anatomic area is considered small.

Cause of Congenital Moles

Familial tendencies exist. Approximately 1 in 20,000 newborns is found to have a large congenital nevus. Melanocytes (pigment-producing skin cells) are found in utero at about 40 days gestation, and it is thought that congenital nevi develop between the 2nd and 6th months of gestation.

Publication Review By: Stanley J. Swierzewski, III, M.D.

Published: 31 Aug 2000

Last Modified: 25 Sep 2015