Oxytocin
Oxytocin (Oxt) is a peptide hormone and neuropeptide. Oxytocin is normally produced by the paraventricular nucleus of the hypothalamus and released by the posterior pituitary. It plays a role in social bonding, sexual reproduction, childbirth, and the period after childbirth. Oxytocin is released into the bloodstream as a hormone in response to stretching of the cervix and uterus during labor and with stimulation of the nipples from breastfeeding. This helps with birth, bonding with the baby, and milk production. Oxytocin was discovered by Henry Dale in 1906. Its molecular structure was determined in 1952. Oxytocin is also used as a medication to facilitate childbirth.
Nipple stimulation
Oxytocin is linked to sexual arousal and pair bonding, but researchers are divided on whether breastfeeding commonly incites sexual feelings. Nipple erection may also result during sexual arousal, or during breastfeeding; both are caused by the release of oxytocin. 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. A survey in 2006 found that sexual arousal in about 82% of young females and 52% of young males occurs or is enhanced by direct stimulation of nipples, with only 7–8% reporting that it decreased their arousal.