Making Milk | The Breast

The human body is quite remarkable! We are living, breathing, walking, talking ecosystems of bacteria and human cells that can literally grow humans inside of us from scratch and then feed them with only our bodies for six months. (Hello, women are amazing!!).

So how can we do it? What is going on under the skin? Sure, we know it is something with hormones from being pregnant, but how does it all work? Many of us who plan on breastfeeding (and even those of us who have breastfed) have at least one moment - maybe hundreds - wondering if we'll make or if we're making enough milk. It is difficult to understand because we cannot see what is happening. We cannot simply look down at our breasts and say "Lefty has a good 5oz in her, let's do this." It may seem silly, but not being able to see our supply leaves a space that is unknown and personally, as a new mom, unknowns were not my friend. 

I believe a large part of this underlying fear of not making enough milk is simply not understanding how the gears work under the hood, if you will. When we understand the mechanisms of how breastmilk is made and what is happening in our bodies, we start to feel more confident that our bodies are capable and powerful. So let's jump in.

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Anatomy of the Breast

Here we focus on the key players in the breast that are involved in milk making. 

How does baby gets the milk? Meet the Nipple. We will talk about different nipple types in a future blog post, but the nipple is where your milk will eject out of. There are anywhere from 1-18 openings (nipple pores) in the nipple, generally around 9 for most of us (1, 2, 3). When stimulated, the nipple becomes firmer, which helps baby latch on (3). When you feed your baby at the breast or pump, the nerves in your nipple send signals to your brain to release/eject your milk, which is AKA a "let down." Simple enough! 

How does baby find the milk? We've got sight and smell working here. Each mom carries a unique scent that is her identifier to her little one (3). Some women may notice tiny glands that look like pimples under the skin around your nipple; these are your Montgomery Glands. Montgomery glands produce an oil that serves a few different purposes - this oil keeps your nipple moisturized and the scent attracts baby towards the breast (3). Breastfeeding mamas should try to avoid heavy perfumed soaps or creams when bathing the breasts and instead opt for unscented, mild soaps or even just water, if you prefer, to avoid masking these oils. So we know smell is a part of the puzzle, let's discuss sight.

Your Areola. She's like the flashing arrow lights on a sign in Las Vegas. The areola is the darker circle surrounding the nipple and comes in many variations of size and color. Under the areola we have many capillaries, which are little networks of tubes for blood to flow through and the blood rushing through them is what causes the pigment of the areola which can range from pink to dark brown (3).  Mamas/expecting mamas - notice the area around your nipples and your nipples darkening? That is because babies see best in high contrast colors (think black and white) in the very early weeks, so our body amps up our hormones and blood flow to darken this area on the breast and make it easier for baby to find and latch on (4). Ah, science!

Who actually makes the milk? Combined with messages from hormones (prolactin + oxytocin) in our bodies due to pregnancy, the Alveoli aka Glandular Tissue is your milk-maker. During pregnancy, we experience a growth of glandular tissue to prepare our breasts to have the capacity to make and store milk (3, 4). Some good visualizations, think of a head of broccoli: the flat part at the bottom - that's your nipple, the stems are the ducts and the bulbs are the end of the broccoli heads - those are your alveoli. Same with a tree: the root of the tree is your nipple where the milk will come out, the branches are your ducts and the leaves/flower buds those are you alveoli. Research says there are anywhere from 15-20 lobes of alveoli (think broccoli florets) in the breast (1, 5). When your breast is stimulated and that oxytocin hormone gets released into your body, it is signaling the cells surrounding the alveoli (myoepithelial cells) to contract and essentially squeeze the alveoli to move the milk out and into your ducts to travel to your nipple and, eventually, to baby (3)! It's a whole series of orchestrated events that have their own built-in conductor!

Then you have your milk ducts. This is the middle man from the alveoli to the nipple and is the way milk is transported through your breast. Women begin developing their ductal system as early as childhood and, as you progress through puberty and pregnancy, these ducts continue growing and developing (3).

What else is in there? You've got a mix of goodies that fill in the rest of the breast such as nerves, fat and connective tissue (3). Certain nerves in the breast are helpful in lactation by providing sensation in the nipple when baby suckles that sends signals to communicate with the brain. Fat fills the breast, provides some support but has little function to the actual production of milk (3, 4). This is why size of your breast is not a reliable indicator of your ability to breastfeed (4). You've also got some ligaments (Cooper's ligaments) and tissue that supports and structures the breast holding everything together. Interestingly, pregnancy (not breastfeeding) cause a loosening of these ligaments and voila! - sagging breasts (4, 6). So whether you breastfeed or not, once you get pregnant, your breasts may sag. The joys of growing a baby in your belly! 

Did you know?

The breast is an organ of our reproductive system (4). 

Each breast develops individually - so it is completely normal if you find one side produces more than the other (4)! 

Small breasts? Large breasts? The size of your breast is not a reliable indication of your ability to breastfeed or produce enough milk. You will, however, want to look for changes in size/color of your breast during pregnancy. If you find you have a low supply, talk with your provider about the changes or lack of changes you experienced during pregnancy in your breasts (4).

Milk is made from components in mom's blood! Many women believe milk is made from water in mom's bodies and worry about hydration to make enough milk. While mom should practice good self-care and always stay hydrated, water intake is likely not going to make a significant difference in milk production. We discuss all about milk making and water here



(1) Ramsay et al. (2005). Anatomy of the lactating breast redefined with ultrasound imagine. Journal of Anatomy, 206, 525.

(2) Love, S. & Lindsey, K. (2010). Dr. Susan Love’s Breast Book (5th ed). Cambridge, MA: Da Capo Press.

(3)  World Health Organization. (2009). The physiological basis of breastfeeding. Infant and Young Child Feeding: Model Chapter for Textbooks for Medical Students and Allied Health Professionals. Retrieved from

(4) Lauwers, J. & Swisher, A. (2015). Counseling the Nursing Mother: A Lactation Consultants Guide. Burlington, MA: Jones & Bartlett Learning.

(5) Zucca-Matthes, G., Urban, C. & Vallejo, A. (2016). Anatomy of the nipple and breast ducts. Gland Surg, 5(1), 32-36. 

(6) Townsend et al. (2012). Sabiston Textbook of Surgery, 19th ed. Philadelphia, PA: Saunders.