As an anatomist, I'm often asked questions about nipples.
Author
Dan Baumgardt
Senior Lecturer, School of Physiology, Pharmacology and Neuroscience, University of Bristol
What is the point of male nipples? Why are nipples considered an erogenous zone? Why, other than a seven-figure salary, did George Clooney agree to wear a Batsuit with nipples for the 1997 film Batman and Robin? All pressing issues, I'm sure you'll agree.
Unlike those adorning Clooney's Batsuit, nipples have important functions for breastfeeding mothers. They contain multiple nerve endings that are sensitive to the stimulation of a suckling baby, which generates the release of the hormone oxytocin, prompting "let-down" of milk from the breast tissue. The nipple contains ducts through which milk is then released for feeding.
The coloured area around the nipple - the areola - serves a purpose too. It contains multiple glands which secrete protective substances onto the skin, most likely to protect the area from damage and chafing during breastfeeding.
Suckling might not be the sole underlying trigger for milk release, however. Sometimes, even the sound of a baby crying stimulates the pituitary gland to release oxytocin in anticipation of a need to feed.
The pituitary also plays an important role in the growth of breast tissue during pregnancy and production of milk, which is controlled by the hormone prolactin.
But you can have too much prolactin. Milky discharge from the nipple in non-breastfeeding patients could be caused by a prolactinoma - a benign tumour of the pituitary gland - which can lead to increased, abnormal prolactin secretion.
Prolactinoma can affect all genders, and can generate other unusual symptoms. Because the pituitary gland is located near the crossing point of the optic nerves, a tumour could compress them as it grows and cause loss of vision.
Breast diseases
Disorders of the breast may present as changes in the nipple. The skin may become itchy, scaled or red - similar in appearance to eczema. The structure of the nipple may also change, becoming inverted or turned inwards, and the skin puckered or dimpled. There may also be a new discharge from the nipple, either clear, or discoloured yellow, green or red by infection, or blood.
Any of these findings, and other significant symptoms like breast lumps, bumps or irregularities, should always be reported to a doctor as soon as they're noticed. Spotting these changes requires vigilance. Regular examination of the breast tissue is essential and make sure you always attend mammogram screenings too.
Although men are often neglected in discussions around breast health, it is crucial for everyone to be aware of any changes in the breast region, regardless of sex. Men also possess breast tissue, albeit in smaller amounts, and can develop gynaecomastia - sometimes referred to informally as "man-boobs". So, while female patients account for 99% of cases of diagnosed breast cancers, men shouldn't consider themselves exempt.
Breast cancer isn't the only cause of nipple discharge, however - discharge can occur during pregnancy and when taking the oral contraceptive pill. Mastitis - infection of the breast tissue - can also cause discharge. Mastitis usually affects nursing mothers but can also develop in non-breastfeeding mothers and, again, in men.
Extra nipples
Many television shows, including The Simpsons and Friends, feature characters with third nipples. An extra nipple isn't just stuff of comedy shows, though - some celebrities including Mark Wahlberg and Lily Allen are reported to have a third nipple. Apparently, Harry Styles has four.
These celebs are part of the estimated 1-6% of the population with an extra nipple, and this is variable across the globe - up to 6% in the USA, but just 0.22% in Hungary. In some cases, it may appear as a pigmented skin spot, very much like a mole, and may go unnoticed and undiagnosed for years. The extra nipple can have breast tissue attached to it, and may respond to circulating hormones to become sore, sensitive or enlarged.
Why do some people have an extra nipple? It could be an echo of the "milk lines" some mammals develop to feed several offspring at the same time. Dogs, cats and pigs for instance, have two parallel lines of multiple teats running from armpit to groin in order to feed large litters. However, in humans, all but two of these nipples usually regress during development of the embryo, though some can remain, leaving an extra nipple. While most occur on these milk lines, some may develop outside of them - on the face, foot or even the genitals.
Placement is important, though. A displaced nipple on the chest, for example, could suggest a different, rare, condition: Poland syndrome.
Poland syndrome is characterised by missing or developed chest muscles, usually the pectoralis major (or pec) on one side of the body. The arms and hands can also be affected.
Abnormalities of the nipple, then, can indicate potentially serious conditions of the breast. But they can also signal neurological and developmental disorders too. It's important therefore to pay close attention to any nipple or breast changes, and consult a doctor as soon as possible.
Dan Baumgardt does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.
