How Breast Milk Is Produced

How Breast Milk Is Produced - Image

Estimated reading time: 9 minutes

“Ah! What is happening?!” This might be one of your first thoughts as you first see milk coming out of your breasts. You’re not alone, mama! Producing breast milk is a new experience, and many women are unfamiliar with it. Perhaps you’ve never seen a baby breastfed or have no idea what to expect. In order to help normalize breastfeeding, let’s take a quick anatomy lesson on how breast milk is produced.

Breastfeeding is Normal For Your Body

Breastfeeding is normal for your body! During puberty and throughout pregnancy, your body prepares to breastfeed (1). As early as 16 weeks of pregnancy, your body makes colostrum, a special milk for newborns (9). Once you deliver your baby and the placenta, hormones tell your body to start producing milk for your sweet newborn (3). The following are the components of your breasts that make breastfeeding happen (3; 9):

  • Glands. Glands contain groups of milk-producing cells.
  • Ducts. Ducts transport milk from the glands to your nipple.
  • The Nipple and Areola. As your baby compresses your areola (the dark area around your nipple), milk flows out of the pores of your nipple.
Breast Anatomy - Glands, Ducts, Nipple, Areola
Breast Anatomy – Glands, Ducts, Nipple, Areola

Click here to learn more about the anatomy of breastfeeding.

How Breast Milk is Produced: The Milk!

The following is the process of how your body makes and gives your baby milk (3; 9):

  1. Milk is made. First, the hormone prolactin tells the milk-producing cells to make milk using water and nutrients from your blood. 
  2. Milk is released. Next, when your baby sucks, the hormone oxytocin causes the muscles around the milk-producing cells to contract. Milk is then released into the milk ducts. This is called the let-down reflex.
  3. Milk travels. The milk then travels through the ducts .
  4. Bon Appetit! Lastly, as your baby compresses the areola, it causes milk to flow through the openings of your nipple into your baby’s mouth. Voila! Fresh milk from the tap!
  5. Supply and Demand. As your baby removes milk from your breasts, your body makes more milk (4). So, the more your baby eats (i.e. demands), the more milk you make (i.e. supply). 

If you think it’s amazing your body can produce milk, just wait until you learn about the remarkable contents of that milk! Click here to learn about the countless benefits of breastfeeding for you, your baby, and more.

How Breast Milk Is Produced: What Is Colostrum & Its Benefits

Breast milk significantly changes during the first few weeks of your baby’s life (7). During pregnancy and in your baby’s first few days, you produce colostrum, or first milk. Since colostrum produces such small amounts, many women think they are not giving enough milk to their newborn. But you are! Your newborn’s stomach is very small. On Day 1, your baby’s stomach is only the size of a marble (4). Your baby only needs less than a tablespoon at each feeding! 

Expressed colostrum has a golden color.
Expressed Colostrum. Image courtesy

If your baby is only getting a little bit of colostrum, you might think, “What does colostrum even do? What is colostrum good for?” Colostrum is the perfect first food for your newborn’s first 72 hours! It has the following properties (7; 9):

  • Thick
  • Golden color
  • High protein
  • Lots of antibodies, protecting against infection
  • Helps baby have first bowel movement
  • Establishes balance of healthy bacteria
  • Easy to digest
  • Produces small amounts

How Breast Milk Is Produced: Colostrum to Milk Transition

Generally by Day 3, your baby’s stomach grows to the size of a ping-pong ball (4). He is ready for a little more milk! Typically during days 5-14 after birth, you produce transitional milk. Transitional milk is a combination of colostrum and mature milk.  

Breast milk at Day 5 - Colostrum to Milk Transition
Breast milk at Day 5 – Colostrum to Milk Transition

Mature milk is designed for your rapidly growing baby. By Day 10, your little one’s stomach grows to the size of an egg. He’ll be ready for the good stuff! By the time your baby is four weeks old, you produce fully mature milk (4; 9). Mature breast milk has the following properties (7; 9):

  • Thinner
  • White (sometimes blueish) color
  • Lower protein
  • Higher in fat and calories
  • Lots 
  • Plentiful

If your baby is born preterm, your colostrum and mature milk will produce more protein, different types of fats, and antibodies that a preterm baby specifically needs (4; 7).  As your baby develops, your breast milk will significantly adapt to meet her needs (9). It’s amazing! Click here to read more about the superpowers of breast milk.

What Does It Feel Like When Your Milk Comes In?

Within the first few days after birth, most women can feel when their milk “comes in”, or starts to transition from colostrum to mature milk. For example, you will feel a heaviness or fullness in your breasts, and they might feel firm (4; 5).  This is normal and should only last a day or two (4).

Your baby may have trouble breastfeeding if your breasts are too full. If this happens, express some milk by hand to soften your breasts before or after a feeding (4). To help prevent engorgement, or painful swelling of the breasts, nurse your newborn baby often (5). 

There might be some discomfort for the first few days of breastfeeding, but you should never have severe or persistent pain. If you’re experiencing pain, ask a lactation specialist for help without delay. 

How Breast Milk Is Produced: Foremilk & Hindmilk

At the beginning of each feeding, foremilk or premilk is the breast milk readily available to your baby (6). This milk starts out low in fat and may appear watery. Throughout each feeding, your milk gradually increases in fat. The milk appears thicker or creamier and is called hindmilk, or postmilk. Hindmilk provides more calories and fat, helping your baby feel full and satisfied (8; 9)! 

Despite what some say, you do not have to nurse on each breast for 15 minutes in order to get your baby the fatty hindmilk. Your baby starts to get that good stuff within the first few minutes of feeding, usually starting at the milk letdown (6; 9). You can’t tell how much fatty milk your baby is getting. As long as your baby is eating effectively, you can let him decide how long he eats.  

Fat content is also determined by how full your breasts are and how long it’s been since the last feeding (6; 9). (Longer it’s been since the last feeding = more full breast = more ‘watery’ the milk.) Additionally, the more empty the breast, the faster your body makes milk. If you need to make more milk, try emptying your breasts more often by feeding your baby more often.

How Breast Milk Is Produced: Supply and Demand

During pregnancy and after delivery, your hormones will help kick start your milk-making. After that, it’s all supply and demand!  As mentioned before, the more your baby breastfeeds, the more milk you make. If you stop breastfeeding, you will consequently stop producing milk. 

Supply and Demand in Breastfeeding.  The more often baby is at the breast sucking, the more milk your body will create.
The more often baby is at the breast sucking, the more milk your body will create.

Because milk production relies on how much your baby is sucking, your milk supply might struggle if you delay breastfeeding until after the first few days. In fact, it is recommended you begin breastfeeding within the first hour after birth. Click here to learn more about the golden hour after birth. If you’re worried about boosting your milk supply, click here for tips on how to produce more breast milk.

A newborn may need to eat as much as 10-16 times a day! During your baby’s growth spurts, your baby will want to eat more. The more she eats, the more milk you will produce, providing more nutrients for your growing baby (7). In the first month of breastfeeding, your breasts will make about 16.5oz of milk a day. By comparison, at six months, you will produce a whopping 27oz per day (9)! While your baby gets older and starts eating other foods, your milk supply will gradually decrease (7). Click here to learn more about how often you should feed your baby.

You’re Amazing, Mama!

Breastfeeding is a beautiful, natural journey! The more a new mom thinks breastfeeding is normal for her body, the more likely she is to breastfeed her baby for an extended amount of time (2). Hopefully, this and other breastfeeding resources help you realize how amazing your body is! You can nourish your little one with the best nutrition out there. You’re amazing, mama!

Kopa Birth’s online childbirth classes allow you to prepare for a natural childbirth in the comfort of your own home, 24/7. Enroll today in our free online childbirth class to learn more about preparing for natural childbirth. 


  1. CAPPA: Childbirth & Postpartum Professional Association. (2016). Lactation Educator Manual (Ninth Edition).
  2. Centers for Disease Control and Prevention (2020, September 28). Breastfeeding. Retrieved October 24, 2020, from
  3. Huggins, K. (2005). The Nursing Mother’s Companion (Fifth Edition). Boston, MA: The Harvard Common Press.
  4. Injoy Health Education. 2016. Understanding Breastfeeding: Your Guide to a Healthy Start (Seventh Edition). Longmont, CO: InJoy Birth & Parenting Education
  5. La Leche League International. Engorgement. Retrieved December 2, 2020, from
  6. La Leche League International. Foremilk and Hindmilk. Retrieved December 2, 2020, from
  7. Meek, J.Y., Yu, W., American Academy of Pediatrics. (2011). New Mother’s Guide to Breastfeeding (Second Edition). New York, NY: Bantam Books Trade Paperback
  8. Rosenthal, M.S. (2000). The Breastfeeding Sourcebook (Third Edition). Lincolnwood, IL: Lowell House.
  9. Simkin, P., Whalley, J., Keppler, A., Durham, J., & Bolding, A. (2016). Pregnancy, Childbirth, and the Newborn: The Complete Guide (Fifth Edition). Minnetonka, MN: Meadowbrook Press.

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Meet Katie Griffin

I’m a registered nurse, Lamaze certified childbirth educator, and the mother of 7. I help women realize their dream of a natural, intimate, and empowering hospital birth.

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“Ah! What is happening?!” This might be one of your first thoughts as you first see milk coming out of your breasts. You’re not alone, mama! Producing breast milk is