Supernumerary breasts are relatively common. They are found along the “milk line,” extending from the axilla to the groin.

Most of them are not noticed clinically until pregnancy occurs. Then, under the influence of the pregnancy hormones, the breasts enlarge in preparation for lactation. It is at this time that soft swellings along the milk line occur, representing supernumerary breasts. During lactation, the extra breasts may produce milk.

Although this image shows a supernumerary breast low in the abdomen, the two most common places for them are in the axilla and directly underneath the normal breast.

These are not dangerous and are generally ignored. If they prove to be a cosmetic problem, they can be removed surgically.

More common than supernumerary breasts are supernumerary nipples. Like extra breasts, these are located in the milk line and are not dangerous.

Unless they are large, they are usually not noticed until a pregnancy. At that time, like the normal nipples, they enlarge and darken.