Most common location of an accessory breast

The most common location of an accessory breast is in the axilla, also known as the armpit. This is due to the embryological development of the mammary glands along the "milk line" which extends from the armpit down to the groin area. During development, most of the milk line regresses except where the breasts normally develop. However, in some cases, additional breast tissue may not regress and can develop into an accessory breast.