• In utero, the breasts develop from the mammary ridge (milk line), an ectodermal thickening that initially extends from the axilla to the medial thigh bilaterally.

• The remainder of the mammary ridge subsequently regresses in early gestation.

• Incomplete involution of the mammary ridge results in an accessory nipple (sometimes with associated glandular tissue) anywhere along this ridge.

• The most common location of an accessory nipple is inferior to the breast.

• Accessory nipples are usually asymptomatic, well-circumscribed, hyperpigmented papules.

• They may become larger during puberty, before menses, or with pregnancy/lactation due to rising estrogen and progesterone (similar to physiologic changes in normal breast tissue).

• Associated glandular tissue may also become tender or swollen.

• The diagnosis is clinical, and no treatment is generally required.