Supernumerary nipple

Overview
A supernumerary nipple (also known as a third nipple, triple nipple, thripple, accessory nipple, polythelia or polymastia) is an additional nipple occurring in mammals, including humans. Often mistaken for moles, supernumerary nipples are diagnosed at a rate of 1 in 18 humans.

Physical Examination
The nipples appear along the two vertical "milk lines", which start in the armpit on each side, run down through the typical nipples and end at the groin. They are classified into eight levels of completeness from a simple patch of hair to a milk-bearing breast in miniature.

Polythelia refers to the presence of an additional nipple alone while polymastia denotes the much rarer presence of additional mammary glands.

Although usually presenting on the milk line, pseudomamma can appear as far away as the foot.

A possible relationship with mitral valve prolapse has been proposed.