Oxytocin is a hormone released from the pituitary gland in the brain. During pregnancy, oxytocin causes labor contractions to begin. Oxytocin also is released when a woman’s breasts are stimulated by suckling or pumping, causing milk to move from the ducts and out the tiny holes in the nipple (let-down reflex). In the first few days after delivery, oxytocin also causes uterine contractions that help shrink the uterus back to its prepregnancy size.

Once breast-feeding is established, your body may release oxytocin when you hear a baby cry, think of your baby, or have sexual intercourse. When this occurs, your breasts may leak milk whether or not you are actively breast-feeding or pumping.

Your body may not release oxytocin when you are anxious, embarrassed, or distracted. You may need to breast-feed in a relaxing, quiet, familiar, private place for let-down to occur.