Francisco Scaramanga, the Man with the Golden Gun, had one. And Mark Wahlberg, Tilda Swinton and Lilly Allen also have a third nipple. Supernumerary nipples (SNs) are relatively common, minor congenital anomalies that are normally benign but are susceptible to hormonal changes and disease processes.
SNs are usually solitary but can number up to eight. Prevalence varies between 0.22 and 6 per cent of the population, depending on ethnicity, sex and geographic region. While 5 per cent of Japanese women have an SN, only 0.22 per cent of white Europeans could claim admission to the triple nipple club. SNs are usually sporadic, but about 6 per cent of cases are familial.
SNs are formed early in foetal development. During the fourth week of embryogenesis, thickened strips of ectoderm known as mammary ridges or lines (milk lines) appear, extending from the axillae to the groin. Mammary buds start to develop as solid, epidermal downgrowths from the mammary ridges during the sixth week. Normally, the mammary ridges only persist in the pectoral region where breasts develop, but when they fail to regress an SN is formed. SNs usually arise within the embryonic milk lines, but have been known to form in other locations, such as the vulva, neck, back and thigh.
If an SN is formed outside the milk lines, Charles Darwin proposed that it may represent an atavism, or tendency to revert to ancestral type. For example, an SN could form in the vulva because this is where dolphins and whales have their breast tissue.
Kajava described eight types of SN in 1915, in a classification still used today. They range from class one – complete with nipple, areola and glandular breast tissue and known as polymastia – to class eight, which is simply a patch of hair known as polythelia pilosa. The most common, class six – a nipple only – is known as polythelia.
If an SN contains glandular tissue it can enlarge during puberty, swell and become tender premenstrually, and lactate. It can develop fibroadenomas, adenomas, cysts, abscesses and mastitis, as well as breast carcinoma. The presence of an SN indicates a much higher risk of kidney or urinary tract malformations, and has also been linked to an increased risk of a range of other conditions, including cardiac arrhythmias, hypertension, peptic ulcer disease and epilepsy.
Some people have made good use of their SN. A famous case from 1827 involved a French woman who had a functioning breast on her left thigh and nursed her five children using all three breasts.