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Everything You Need to Know About Breast Milk Production and Supply

How do your breasts make milk, and what can you do to support a strong, healthy supply for your baby? We look at everything you ever wanted to know about producing the amazing substance that is breast milk.

What did you think about breast milk before you started breastfeeding? Lots of parents don’t give it a second thought — it’s just breast milk!

But once you’ve started your breastfeeding journey, you can’t help but be amazed. Not just by how astonishing breast milk is, but also by how it’s made!

Breast milk production is straight-up fascinating.

Breast milk production

You’ll hear a few terms a lot in breastfeeding: Hormones. Supply-and-demand. Letdown reflex. Lactogenesis. (Well, maybe not that one.)

Breast milk production is both simple and complex. It requires a complex mixture of hormones, behaviors, and bodily responses. It also comes down to basic supply and demand.

Let’s look at how breast milk gets produced.

Before baby

When you’re approximately 6 weeks pregnant, pregnancy hormones begin to order your body to develop milk-making cells called lactocytes in your alveoli, the grape-like clusters attached to your milk ducts.

By the second trimester, these lactocytes will start producing colostrum. This stage of breastfeeding is known as Lactogenesis I. (See below.)

Why would your body do this, though? After all, your baby won’t arrive for at least 20 weeks or more.

Colostrum production at this stage is a side effect of your pregnancy hormones — your prolactin levels are on the rise. But by 16 weeks of pregnancy, lactocytes start producing colostrum in preparation for your baby’s imminent arrival.

Breastfeeding trivia: Colostrum has a long history of being regarded with disdain. From cultures in Europe, Africa, and the Indian subcontinent, new parents have often been told not to nurse their baby until the colostrum has run out. Today we know much more about the considerable health benefits of colostrum for babies.

After baby

Once you’ve had your baby—congratulations, by the way!—and delivered the placenta, your progesterone levels drop. Dramatically.

The sudden change in hormones triggers the next stage of lactation, Lactogenesis II.

That means milk! (At least, milk 30-40 hours after having your baby.)

However, getting your baby latched on and nursing is essential to this process. This sucking stimulates your milk-producing cells and lays the foundation for your milk supply.

IBCLC tip: Get your baby skin-to-skin, latched on, and nursing within an hour of being born. Skin-to-skin contact is especially beneficial for stabilizing your baby’s temperature and heart rate and stimulating breastfeeding hormones.

Establishing Lactation

The first weeks of breastfeeding are critical to your milk production and supply. Each time your baby nurses (e.g., removes milk from your breasts), your prolactin levels surge and helps you create more milk. It also helps your milk shift from colostrum to transitional to mature milk.

While hormones play a role in this stage of breastfeeding, as your supply begins to establish, it becomes more about supply and demand. The more frequently you breastfeed, the more milk you produce.

Don’t feel like your baby isn’t getting enough milk or that there’s something wrong with your milk if they need to feed a lot. You might feel like they’re constantly attached to your breast—and they might be, really!—but newborns have tiny tummies. It doesn’t take much to fill them up.

And the more they feed, the more milk you can produce. So feed on demand rather than on a schedule.

Note: If you’re exclusively pumping, it’s fine to stick to a schedule. However, in the early days, that schedule should mimic a baby’s feeding patterns so you can maximize your milk supply.

It’s also essential to pace-bottle feed with a slow flow nipple and keep feeds to 2-3 hours during the day and no more than 4-5 hours at night during the early weeks. While tempting to give more in a bottle for a longer stretch, waking to feed is protective against SIDS.

Types of milk

Think all breast milk is the same? You might be surprised to learn that there are three different types of breast milk, each one uniquely composed for your baby’s needs as they start breastfeeding.


The first breast milk that you’ll make is colostrum. Colostrum production starts well before your baby is born, somewhere around 16 weeks, and will continue to be produced for a few days after your baby is born.

Colostrum is thick, sticky, and made up of proteins, sugars, fats, salts, vitamins, and antibodies that are designed for your baby—it’s perfect, complete nutrition for a newborn. What does colostrum do?

  • Kick starts your baby’s immune system.
  • Coats your baby’s stomach and intestines to prevent illness and inflammation
  • Works as a laxative so your baby can pass meconium
  • Prevents jaundice and low blood sugar
  • Provides essential nutrition for your baby’s brain, eye, and heart development

Colostrum isn’t made in huge quantities—you’ll likely only make a couple of teaspoons a day. As we said, though, your baby has a tiny tummy. That amount is plenty for them.

Transitional milk

Transitional milk is—you guessed it!—transitional. It’s the stage of breast milk between colostrum and mature milk.

Transitional milk contains more calories than colostrum and has high levels of fat, lactose, and water-soluble vitamins.

This stage of milk is when you may experience engorgement. When your transitional milk comes in, your breasts will become fuller, heavier, and harder. Engorgement itself only lasts for a few days, but you’ll continue producing transitional milk for up to 2 weeks after delivery.

Mature milk

Mature milk is what you’ll produce for the duration of your breastfeeding journey. Mature milk is higher in water content than colostrum or transitional milk—it’s 90% water, which is vital for keeping your baby hydrated. (That’s why you don’t need to give your baby water while they’re exclusively breastfeeding.)

That other 10% is full of carbs, proteins, fats, vitamins and minerals, and antibodies. It’s what helps your baby grow, gives them energy, and supports their immune system.

Note that while you’ll only produce mature milk from here on out, that doesn’t mean that your milk itself stays the same. Breast milk has the unique ability to adapt to your baby’s nutritional and immune system needs. Here are a few examples:

  • Breast milk provides illness-specific antibodies when either your baby OR you are sick.
  • Frequent nursing during growth spurts increases fat content in milk
  • Nighttime breast milk contains more serotonin to help your baby sleep
  • Breast milk carries the flavors of your diet, influencing your baby’s palate from early on

Let’s talk about Foremilk and hindmilk

Foremilk and hindmilk are big topics of discussion among breastfeeding parents. (And yes, IBCLCs, too!) What do you need to know about them, though?

First, it’s important to remember that once your mature milk comes in, your breasts only make one type of breast milk: Yours! There’s not a separate production cycle for foremilk and hindmilk.

What happens is this: When your baby nurses, breast milk gets squeezed out through your milk ducts via the letdown reflex. The fatty parts of your milk are stickier than the rest, so they cling to the walls of your ducts. However, as your baby continues to nurse and your breasts get emptier, the fat gradually dislodges, creating what is referred to as hindmilk.

This process is gradual—it’s not like your milk automatically becomes fattier or richer after nursing for 10 minutes. You can, though, increase the fattiness of your milk by nursing frequently. Empty breasts produce fattier breast milk.

Milk Production: Your Breasts, Your Brain, Your Baby, and Your Milk

Breast milk doesn’t make itself! Well, it does. But it requires several things to work in synchronization: Your breasts, your brain, your baby, and your milk.

Your breasts

Milk production takes place in your breasts. More specifically, within the alveoli, there are clusters of cells in your breasts. Your alveoli make the milk, which is then drawn out through your milk ducts through your breast to your baby.

It’s a common misconception that you need large breasts to breastfeed successfully. Your cup size actually has nothing to do with it. Instead, it’s the number of alveoli in your breasts. Think of your alveoli like the number of cups of milk you can keep in your breasts for your baby. The more cups you have, the more milk you can store.

But even then, you can successfully breastfeed no matter your storage capacity. Your baby may need more or longer nursing sessions, but your breasts are powerhouses when it comes to adapting to your baby’s nutritional needs.

Your brain

Your brain—specifically your endocrine system—plays a significant role in milk production.

When your baby nurses, your brain releases two important breastfeeding hormones: prolactin and oxytocin:

  • Prolactin tells the alveoli to make milk. Prolactin levels are high after you give birth and stay high until you wean.
  • Oxytocin helps the muscles surrounding your alveoli contract and release milk

Your hormones are also responsible for the rise and fall of milk production throughout the day. Your milk volume is higher in the early morning and lowers in the evening, thanks to prolactin.

The letdown reflex

This release of milk is called the letdown reflex, also known as the milk ejection reflex.

Your letdown comes courtesy of oxytocin. For some breastfeeding parents, it’s noticeable, including a tight, achy, tingling sensation. Letdown can be accompanied by milk leaking from the non-nursed breast.

Other parents may not notice it—and that’s normal too.

One of the fascinating things about your letdown reflex is that it’s what’s known as a partially conditioned reflex. That means that you can train your body to trigger it. What does this mean for milk production?

The easier and faster your letdowns are, the more milk you can produce! You can coax your body to release milk by associating triggers with your letdown. Set up pre-nursing or pumping rituals, such as:

  • Taking a warm bath or shower
  • Practicing deep breathing exercises
  • Listening to relaxing music
  • Drinking a cup of tea
  • Nurse or pump in the same (comfortable!) place

Hormonal birth control and breastfeeding

Many breastfeeding parents experience what’s known as “lactational amenorrhea,” which is when your menstrual cycle is delayed by breastfeeding. However, this doesn’t always prevent pregnancy. For parents who are wanting to avoid pregnancy, hormonal birth control is generally a safe option.

That being said, hormonal birth control can impact your milk supply, even progestin-only birth controls that are often recommended for breastfeeding parents. Talk to your lactation consultant and healthcare provider about your breastfeeding goals and birth control.

Your baby

When it comes to keeping your milk supply going strong, your baby does more than create the demand. The way your baby nurses has a big part to play.

We tell breastfeeding parents—early and often—that a deep latch is critical to nursing.

How your baby latches onto your breasts directly influences how well they transfer milk, and how well they transfer milk influences how much milk is left in your breasts following nursing. If there is excess milk, your body won’t get as strong a signal to produce more.

Your milk

There are many, many amazing things about breast milk. One of them is a whey protein in the milk known as Feedback Inhibitor of Lactation (FIL).

This protein essentially oversees the supply and demand process of breastfeeding, regulating the amount of milk you make by telling your alveoli to fill up with milk when your breasts have been emptied and when to stop filling them up if they’re not being emptied.

Milk Supply Issues

Are you making enough milk? Likely. If a baby is growing and happy, it’s unlikely that there is a supply issue. But that doesn’t mean breastfeeding parents don’t worry about how much milk they make.

“Most breastfeeding parents question their milk supply at some point,” says Nest Collaborative IBCLC, Robin Williams. “It’s hard to trust our bodies sometimes!”

That being said, if you’re genuinely concerned about milk supply, it’s something you can always ask an IBCLC about. Here are the signs to look for with oversupply and low supply.


Oversupply may sound like a problem that many breastfeeding parents would like to have, but it poses its own set of challenges.

To start, an abundant milk supply often means a fast milk flow. For babies, especially newborns, it’s hard to control the flow. This leads to gagging, coughing, or clamping down on the nipple to slow the milk down.

Another challenge for managing to breastfeed with oversupply is lactose overload. If your baby fills up on foremilk—which is the milk earlier in a nursing session—they can end up with lactose overload. (This used to be known as foremilk/hindmilk imbalance, but the terminology has changed in recent years.)

Foremilk is higher in lactose, lower in fat than hindmilk, and passes through their digestive systems faster than the lactose can be processed. The result: flatulence and frothy, explosive stools that are accompanied by pain and screaming.

Oversupply can also be uncomfortable for the parent. Letdowns are sometimes more noticeable—and painful—for those with oversupply. Breasts can become engorged when there’s not enough milk removal, leading to clogged ducts and mastitis.

Managing oversupply

If you have oversupply, it can be frustrating. Before you do anything, talk to a lactation consultant. They can help you determine if you have actual oversupply, what’s causing it, and then find solutions. But rest assured: Making breastfeeding comfortable and manageable is an achievable goal. Here are a few practical approaches:

  • Nurse in a laid-back position to slow your milk flow
  • Only nurse on one side per feed
  • Use block feeding to slowly and carefully reduce supply
  • Use breast massage to get more hindmilk, break up clogs, and minimize discomfort
  • Reduce engorgement by nursing, pumping, or expressing, but only to relieve pain, not to empty breasts
  • Try cold compresses or cabbage leaves to ease pain and decrease the supply

Low supply

Low supply is something that lots of breastfeeding parents are concerned about. It’s understandable. Your milk is your baby’s food, and you want to have plenty of it.

It’s easy to look at parents with oversupply, those with babies in the 99th percentile, or parents who pump 8 oz in one sitting and think that you’re not making enough.

  • Is my baby gaining weight along THEIR curve?
  • Are they meeting their developmental milestones?
  • Are they producing enough wet and dirty diapers?

If they are, then it’s very likely that your supply is just fine.

What are signs of a low supply?

  • Your baby isn’t gaining weight despite being fed on demand without restrictions (e.g., feeding on both breasts)
  • Not meeting developmental milestones
  • Not making enough wet and dirty diapers each day

If the answer is yes, then it’s essential to speak with your baby’s pediatrician as well as an IBCLC to make sure you’re protecting your baby’s health and boosting your milk supply.

Managing low supply

  • Nurse frequently
  • Check your baby’s latch and position
  • Add pumping and/or hand expression to your breastfeeding routine several times a day.
  • Use breast massage to help empty your breasts during a feed
  • Self-care: Eat, drink plenty of water, and get enough rest

Supplements and medications may be options for you if you’re concerned about your supply as well, but these options should always be explored with the guidance of an IBCLC.

Learn more about low supply here.

Extended Nursing and Your Milk Supply

We have no idea where the idea got started that breast milk loses its value after a certain time.

It’s categorically, unequivocally wrong.

Although some toddlers are frequent nursers, they gradually taper off as they grow. This decrease impacts your supply, but it doesn’t make the milk you produce less valuable.

No matter whether you nurse for 3 months or 3 years, breast milk has a stellar nutritional profile, constantly adapting to meet your child’s needs as they grow. Consider the following research:

Numerous studies have found that breastfed toddlers (between 1-3 years old) experience fewer illnesses, illnesses of shorter duration, and lower mortality rates.

Ask questions and ask for help

Worried about your milk supply? We want all parents to feel confident about their breastfeeding experience. We’re here to answer your questions and help you find solutions. Book a convenient online video appointment with one of our IBCLCs today.

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