The stimulation of women's nipples promotes the production and release of oxytocin and prolactin.[3] 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.[4][5]
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.[3] 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.[6] 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.[7][8] 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.[9]