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Stimulation of nipples is a common human sexual practice, either for itself or as part of other sexual activities. The practice may be performed upon, or by, people of any gender or sexual orientation. Young adult women and men report that breast stimulation not only induces their sexual arousal but enhances it when already aroused.
The male or female breast, nipple and areola develop similarly in the foetus and during infancy. At puberty the male's breasts remain rudimentary but the female's develop further, mainly due to the presence of oestrogen and progesterone, and become more sensitive. 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.
The touching by one person of the breasts and nipples of another is normally an indicator of intimacy, and allowing breasts to be touched is an indication of either an emotional bond and trust between the individuals or, if unwelcome, of submission. Breasts, and especially the nipples, are highly erogenous zones, for both men and women, and have a heightened sensitivity, the stimulation of which may result in the production of erotic sensations or sexual excitement. The touching of nipples can be a form of foreplay giving rise to nipple erection and sexual arousal.
Erect nipples are the most prominent indicators of a female's sexual arousal, and the female's sexual partner may find their partner's arousal and erect nipples as their own erotic stimuli. Some people achieve their own sexual arousal by sucking on a nipple or by the sight of an erect nipple, including through clothing. The practice of an adult suckling on a female's breast is sometimes referred as erotic lactation, while a person who is sexually aroused by the sight of a female's breast may be a breast fetishist. A person may experience a spontaneous erection of the nipples, with all the associated physiological changes, as a result of exposure to erotic stimuli or as a reaction to cold.
Any physical contact with nipples may result in their stimulation. They can be stimulated orally, digitally, manually or by the use of an object. A person's nipples may be stimulated orally by a sex partner licking, sucking, biting or blowing on the nipples. Other ways of stimulating nipples include fondling or rubbing them with the hands or other body part, or by using a soft object. A person may self-stimulate their nipples.
The stimulation of a woman'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 a woman'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 can result in a female's sexual arousal, with a resulting physiological response, including the erection of the nipples. A 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. 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. A survey in 2006 has 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. A 2011 study using magnetic resonance imaging has shown that the area of the sensory cortex in a woman's brain associated with the genitals, is aroused by stimulating her nipples. The same brain areas connected to genitals were aroused as well in men who stimulated their nipples.
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. During this period, the nipples can become extremely sensitive to touch and further stimulation can be painful. The amount of prolactin can be an indicator for the amount of sexual satisfaction and relaxation. Unusually high amounts are suspected to be responsible for impotence and loss of libido (see hyperprolactinemia symptoms).