Nipple stimulation or breast stimulation is a common human sexual practice, either by itself or as part of other sexual activities. The practice may be performed upon, or by, people of any gender or sexual orientation. Adult women and men report that breast stimulation may be used to both initiate and enhance sexual arousal.
The male or female breast, nipple and areola develop similarly in the fetus and during infancy. At puberty, the male's breasts remain rudimentary but the female's develop further, mainly due to the presence of estrogen and progesterone, and become much more sensitive than the male ones. All breasts have the same number of nerve endings no matter how large they are. Accordingly, smaller breasts are more sensitive while larger breasts may require more forceful stimulation. Breasts, and especially the nipples, are highly erogenous zones, for both men and women, and have a heightened sensitivity, the stimulation of which may produce sexual excitement. Erect nipples can be a prominent indicator of a female's sexual arousal, and the female's sexual partner may, as a result, find this erotically stimulating.
The stimulation of women's nipples promotes the production and release of oxytocin and prolactin. During the stimulation of the nipples, large amounts of oxytocin are released, which would normally prepare women's breasts for breastfeeding. Besides creating maternal feelings, it also decreases a woman's anxiety and increases feelings of bonding and trust.
The release of oxytocin in a woman's body can lead to sexual arousal, with a resulting physiological response, including the erection of the nipples. Nipple erection is due to the contraction of smooth muscle under the control of the autonomic nervous system and is a product of the pilomotor reflex which causes goose bumps. Nipple erection can also be caused by a mild tactile stimulation or as a response to cold temperature in both males and females. Nipple erection may also result during sexual arousal in females and males, or during breastfeeding. Both are caused by the release of oxytocin. A survey in 2006 found that sexual arousal in about 82% of young females and 52% of young males arises or is enhanced by direct stimulation of nipples, with only 7–8% reporting that it decreased their arousal. An erection of the nipples makes them even more sensitive to the touch. Some women can achieve an orgasm as a result of nipple stimulation; this may be because the area of the sensory cortex in a woman's brain associated with the genitals is aroused by stimulating her nipples. A 2011 study indicated that the same brain areas connected to genitals are aroused.
Prolactin produces sexual gratification after sexual activity. Prolactin represses the effect of dopamine, which is responsible for sexual arousal, and is thought to cause the sexual refractory period following orgasm during which the individual (typically a male) does not desire any further sexual stimulation.