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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, but is more commonly performed on women. Breast and nipple stimulation of women are a near-universal aspect of human sexual activity, and stimulation of nipples of males is not as common.
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 the nipples can be a form of foreplay giving rise to the sexual arousal of the female and an erection of her nipples.
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 female's 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.
Nipples can be stimulated orally, digitally, manually or by the use of an object. Oral nipple stimulation involves a sex partner stimulating a person's nipples by licking, sucking, biting or blowing on the partner's nipples. Other ways of stimulating nipples include fondling or rubbing them with the hands or by using a soft object. Some people self-stimulate their nipples.
Nipples may become erect due to the contraction of smooth muscle under the control of the autonomic nervous system and are 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.
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 the breast for breastfeeding. Besides creating maternal feelings in a woman, it also decreases her anxiety, increases human bonding and trust.
The release of oxytocin can also result in a female's sexual arousal, with the resulting physiological effects including the erection of the nipples. An erection of the nipples makes them even more sensitive to touch. An orgasm by nipple stimulation can be achieved in some women. 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.
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).