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In its most general form, a nipple is an appurtenance from which a fluid emanates, in this instance breast milk, to nurture a mother's young.

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Mammals typically have an even number of nipples arranged around bilaterally. In the primitive mammals (monotremes such as the platypus), the mammary glands empty onto the skin without a nipple.

In human anatomy, the two nipples are located near the center of the breasts, surrounded by an area of sensitive, pigmented skin known as the areola. The pigments of the nipple and areola are brown eumelanin (a brown pigment) and to a greater extent pheomelanin (a red pigment). The nipple and areola of males and females can be erotic receptors, or considered sex organs. Stimulation or sexual arousal can cause the nipples to become erect, due to the release of the polypeptide neurotransmitter oxytocin. Breastfeeding or exposure to cold temperatures often has this effect as well.

The average projection and size of human female nipples is slightly more than 3/8 inches (0.4 in./10mm.) [1]. Pregnancy and nursing tend to increase nipple size somewhat, and this increase may remain permanently thereafter. Pregnancy also increases the pigmentation of the nipples. The erection of the nipple is partially due to the cylindrically arranged muscle cells found within it. In many women there are small bulges on the areola, which are called 'Montgomery bodies'.

Embryologically, nipples develop along the 'milk lines' which in humans extend from the axilla (armpit) down to the pubis (groin) on both sides. Most mammals develop multiple nipples along each milk line, with the total number approximating the maximum litter size, and half the total number (i.e. the number on one side) approximating the average litter size for that species. Most people develop two nipples (one on each breast) but some have supernumerary nipples. Occasionally, these have lactiferous glands attached.

Sometimes, babies (male or female) are born producing milk. This, called 'witch's milk', is caused by maternal estrogens acting on the baby and is quite normal. Witch's milk disappears after several days.

Nipples on male mammals



See also


This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Nipple". A list of authors is available in Wikipedia.