How the Body Makes Breast Milk

Woman breast feeding
@crystalmariesing via Twenty20

Human breast milk is an amazing fluid. It’s nutritious, comforting, and helps protect newborns and infants from infection and disease. It changes throughout the day and over time to adjust to a child’s needs, even when the child is sick. Breast milk is undoubtedly the ideal food for a human child. And, while they try, scientists can’t replicate it in a laboratory. There’s just no man-made equivalent.

Only a mother can produce it for her child. Here’s how your body makes breast milk.

The Parts of the Milk-Making Process

The structures that make up the female breast protect, produce, and transport breast milk. If you’re thinking about breastfeeding, you may be wondering how it all works. It may be easier to understand when you know about all the parts that work together to make it happen.

On the outside, skin surrounds the breast. The areola is the darker circular or oval area on the breast, and the nipple protrudes from the middle of the areola. When a baby latches onto the breast to remove breast milk, the entire nipple and all or part of the areola is taken into the mouth. There are also small bumps on the areola called Montgomery glands. The Montgomery glands produce an oil that cleans and moisturizes the nipples and areola.

On the inside of the mature breast:

  • Adipose tissue is fat tissue that cushions and protects the breast.
  • Connective tissue and ligaments provide support for the breasts.
  • Glandular tissue is milk-making tissue. It contains the milk ducts and alveoli.
  • Alveoli are small grape-like groups of sacs or milk glands that make the breast milk.
  • The milk ducts carry the breast milk from where it’s made in the alveoli, through the breast, and out to the baby.
  • Smooth muscle cells called myoepithelial cells surround the alveolar glands and milk ducts. When they contract, they squeeze the milk out of the milk-making glands and through the ducts.
  • Nerves that lead from the nipple and areola send a signal to the brain to stimulate the release of breast milk and the production of more milk.

How Breast Milk Is Made

A woman’s body is remarkable. Not only can it grow another human being, but it can also provide all the nourishment that the child needs to grow and develop. The preparation for breast milk production begins even before a woman is born and continues through puberty and pregnancy. Once full production occurs after the birth of a child, it can go on for months or even years.

The Beginning

At birth, you have all the parts of the breast that you’ll eventually need to make breast milk, but they are not developed. During puberty, hormone changes cause the breasts to grow and the milk-making tissue to begin to develop. Each month after ovulation, you may notice an increase in the size and tenderness of your breasts as your body and your breasts start to prepare for a pregnancy and breastfeeding. If there’s no pregnancy, the fullness and tenderness subside, and the cycle repeats.

But, when a pregnancy does occur, the breasts continue to grow and develop to prepare for lactation.

During Pregnancy

In the very beginning of your pregnancy, your breasts are already changing. In fact, these slight changes may be the first signs you notice that lead you to take a pregnancy test. During pregnancy, the breasts fully mature. By the time you find out you're pregnant, your body is well on its way to preparing for breast milk production. The hormones estrogen and progesterone cause the milk ducts and milk-making tissue to grow and increase in number. The breasts grow in size. There is more blood flow to the breasts so that veins may become more visible.

The nipples and areola become darker and larger. The Montgomery glands get bigger and look like small bumps on the areola.

During the second trimester, by about the sixteenth week, your body starts to produce the first breast milk called colostrum. You may even begin to see small drops of white or clear fluid on your nipple. If your baby were to arrive early, your body would already be able to make breast milk. This stage of milk production is called lactogenesis I. It lasts from about the 16th week of pregnancy until the second or third day postpartum.

Immediately After the Birth of Your Baby

When your child is born and the placenta leaves the body, estrogen and progesterone levels drop and the hormone prolactin rises. This sudden hormonal shift signals an increase in the production of breast milk. Your newborn will receive the small amount of colostrum you started making during pregnancy for the first day or two, but after that, you’ll begin to notice an increase in the amount of breast milk that's filling up your breasts. This stage of milk production is called lactogenesis II. It lasts from the second or third day postpartum to the eighth day.

Maintaining Breast Milk Production

In the beginning, the body makes breast milk automatically whether you want to breastfeed or not. But, after the first week or so, the release of the milk-making hormones and the continuation of breast milk production is based on supply and demand. If you want to establish and maintain a healthy milk supply for your child, you have to breastfeed or pump frequently.

Frequent breastfeeding stimulates the nerves in the breast to send a message to the pituitary gland in your brain. The pituitary gland releases the hormones prolactin and oxytocin. Prolactin tells the milk-making glands in your breast to make breast milk. Oxytocin signals the let-down reflex to release the milk. It causes the alveoli to contract and squeeze the breast milk out into the milk ducts. The milk is then removed by the baby or a breast pump. If you breastfeed every one to three hours (at least eight to 12 times a day), you’ll be emptying your breasts, keeping your prolactin levels up, and stimulating milk production to continue. This stage of full milk production begins about the 9th day and lasts until the end of breastfeeding. It is called galactopoiesis or lactogenesis III.

How to Stop the Production of Breast Milk

Whether or not you choose to breastfeed, your body and your breasts will still get ready to make breast milk for your child. If you do breastfeed, you will make breast milk until you decide to wean. As your baby breastfeeds less and less, your body will get the message to make less breast milk. If you do not breastfeed, you will still make breast milk after your baby is born. However, if you do not put the baby to the breast or pump the breast milk, your body will slowly stop making milk. Either way, you may still have leaking and continue to produce a small amount of breast milk for a little while as you're drying up. Then, the glandular tissue will shrink down, and the breast will return to its pre-pregnancy state. This stage of lactation is called involution.

How Breast Size Affects Milk Production

The amount of fat tissue in your breast determines your breast size, not the amount of glandular tissue. Women with larger breasts have more fat tissue than women with smaller breasts, but that doesn't mean they have a greater amount of milk-making tissue. Almost all women have enough milk-producing tissue to establish and maintain a healthy breast milk supply for their child. So, the size of your breasts doesn't really matter. If you have smaller breasts, the only concern is that they may not be able to store as much milk as larger breasts. Therefore, your baby may get less milk at each feeding making it necessary to breastfeed more often.

Making Breast Milk Without a Pregnancy

If you’re building your family through adoption or the use of a surrogate, you may still want to try to breastfeed. Creating a breast milk supply without going through a pregnancy is called induced lactation. You can do it, but it does require dedication and advance preparation. It starts with a medication protocol months before the baby is due to arrive. Birth control pills with progesterone and estrogen mimic the hormones of pregnancy and stimulate the growth of the breast tissue.

Certain medications or herbs that act as galactogogues are added to increase prolactin levels. Then, a few weeks before the baby will arrive, you should begin pumping the breast to provide breast stimulation and the regular removal of breast milk. Induced lactation works for some women, but not all. Even when the protocol is followed correctly, some women cannot make enough breast milk for their child and may need to supplement.

Galactorrhea

Galactorrhea is the production of breast milk that isn’t related to pregnancy and breastfeeding. It produces a milky discharge from the nipples. Galactorrhea doesn’t only affect women; it can also occur in men, newborns, and children. Elevated levels of prolactin are associated with galactorrhea, but it is also seen without high prolactin levels. It can result from certain medications, hypothyroidism, kidney disease, breast stimulation, pregnancy, a non-cancerous pituitary tumor in the brain, or another cause. The treatment of galactorrhea depends on the cause, so if you’re producing a milky discharge from your breast, see your doctor.

Sources:

Academy of Breastfeeding Medicine Protocol Committee. ABM clinical protocol# 9: use of galactogogues in initiating or augmenting the rate of maternal milk secretion (First revision January 2011). Breastfeeding Medicine. 2011 February 1;6(1):41-9.

Hassiotou F, Geddes D. Anatomy of the human mammary gland: Current status of knowledge. Clinical Anatomy. 2013 January 1;26(1):29-48.

Huang W, Molitch ME. Evaluation and management of galactorrhea. American Family Physician. 2012 June 1;85(11).

Newman J, Pitman T. Dr. Jack Newman's Guide to Breastfeeding. Collins; 2014.

Wambach K, Riordan J, editors. Breastfeeding and human lactation. Jones & Bartlett Publishers; 2014 August 15.

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