How Lactation Works

Your body’s ability to produce and provide milk to your baby is controlled by hormones in your body, primarily one called prolactin. Levels of this hormone rise after delivery, enabling you to feed your baby immediately. Milk is produced automatically at first, but in order to continue producing milk you need the stimulation of your baby’s sucking (or similar stimulation for a breast pump), which releases prolactin. Without stimulation at least once a day starting from a few days after delivery, women lose the ability to nurse.

Another hormone, oxytocin, sets in motion the release of milk from ducts in your breast, sometimes called “letting down.” Oxytocin is also stimulated by sucking, but even seeing your baby or hearing her cry can release the hormone and cause milk to flow.

In the first few days after delivery, your milk is yellowish and thick; this protein- and antibody-rich first milk is called colostrum. Because early milk is particularly high in nutrients for the newborn, women are encouraged to try breast-feeding immediately after delivery and during the first days or weeks of their baby’s life, even if they are not able to continue breast-feeding for the long term. The colostrum will turn into a light yellow or whitish milk after two to four days.

Most women produce more than enough milk to feed a baby. The actual volume of milk you produce varies according to how much your baby demands -- a very convenient system!

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What a woman eats during pregnancy can have an important effect on her health and the health of her baby -- even when the baby becomes an adult. For more information on nutrition during and after pregnancy for yourself and your baby, read The Harvard Medical School Guide to Healthy Eating During Pregnancy.

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