All breasts have the same number of nerve endings.

The male or female breast/nipple/areola complex arises from a common mammary stem cell and develops similarly in the foetus and during infancy. At puberty the male’s breasts remain rudimentary but the female’s develop further, mainly through oestrogen and progesterone stimulation, and become more sensitive. Female breasts serve both nutritive and sexual functions, unlike other primates they develop at puberty before lactation is necessary. Their sexual attraction is through size, shape and their areolae but also, when unrestrained, their jiggling movements. Small breasts are more sensitive than large. Pregnancy and lactation increase their size. Breast feeding releases oxytocin (milk release) and prolactin (milk secretion), other functions have been proposed for the latter. The pigmented areola contains tubercles of Montgomery that secrete a fluid protecting the skin and creating an olfactory signal for baby and possibly lover; areola corrugation immediately after orgasm physically signals that orgasm has occurred. Male and female (non-pregnant) nipple stimulation has been claimed to induce prolactin secretion but confirmation is needed. Young adult women and men report that breast stimulation not only induces their sexual arousal but enhances it when already aroused.