Surplus nipples can be traced back to an incomplete regression of the milk line in the unborn child in the womb.
They are found in two to three percent of newborns and can occur frequently in families. A connection with kidney malformation is controversially discussed. Supernumerary nipples usually occur on one side, occasionally with an areola and single hairs. The technical term for this is polythelie.
Surplus nipples usually occur in the immediate vicinity of the breast above the pectoral muscle or near the armpit, less frequently on the abdomen. After removal, the tissue is examined for fine tissue in order to obtain certainty about the benign findings.