Breast Milk Production – The Magic & Science of Breastfeeding

If you’re pregnant or holding a brand-new baby in your arms, you might be wondering: How does breast milk production work? Like, where does it come from? How does your body know what to do? And why does it sometimes feel like it’s not working the way it’s supposed to?

You’re not alone in asking. Breast milk production feels like a superpower—but also a mystery, especially when you’re tired, overwhelmed, and trying to figure it all out in real time. Let’s break it down together, mom to mom, so you know what to expect, what’s normal, and how to support your body in doing what it’s designed to do.

How Breast Milk Production Begins

Breast milk production starts long before your baby is born. As early as halfway through pregnancy, your body begins building the system it needs to feed your baby. Hormones from pregnancy help grow your milk ducts and form clusters of tiny milk-making sacs called alveoli.

The Role Of Hormones

Here’s what happens:

• During pregnancy: High levels of estrogen and progesterone prepare the breasts, but they also block milk from flowing. Meanwhile, colostrum—the first milk—starts being produced.
• After birth: Once the placenta is delivered, progesterone drops fast. This signals the start of lactogenesis II, or the big milk surge. Prolactin takes over and milk starts to flow within 30–40 hours. If you’ve had a c-section or certain medical conditions (like PCOS or diabetes), this may take closer to 4–5 days.

Your baby’s tummy is tiny—just a few drops of colostrum are enough per feed in the early hours.

Breastfeeding as soon as possible after birth helps trigger more prolactin, which supports stronger, more consistent breast milk production.

The Let-Down Reflex: When Milk Gets Released

Once your milk is in, your body starts using another hormone—oxytocin—to move it out. Oxytocin causes the tiny muscles around your alveoli to squeeze, pushing milk into the ducts and out of your nipple. This is called the let-down reflex.

Some people feel a tingle or fullness when this happens, others feel nothing at all. Both are normal.

Let-down can be triggered by suckling, crying, or even just thinking about your baby. It’s part of your body’s incredible way of staying in sync with your baby’s needs.

What Helps (And Hurts) Breast Milk Production

Once milk is flowing, your body switches into what’s called lactogenesis III—also known as the maintenance stage. At this point, milk supply runs on demand: the more milk your baby takes, the more milk your body makes.

How to Encourage Breast Milk Production

• Feed frequently—8 to 12 times a day is totally normal early on
• Make sure your baby is latching and drinking well
• Pump or hand express if your baby can’t nurse effectively
• Use breast massage or gentle compression while feeding
• Prioritize skin-to-skin contact
• Don’t skip night feeds (prolactin is higher at night!)
• Keep stress levels low—your mental health affects hormones too

What Can Interfere With Breast Milk Production

• Scheduled feedings that limit nursing sessions
• Supplementing with formula without medical need
• Unrelieved nipple pain
• Health issues like retained placenta, PCOS, or thyroid conditions

Milk tends to be more abundant in the morning and slowly decreases throughout the day—but fat content increases later in the day too, helping baby feel satisfied.

When Milk Is Delayed

Sometimes, your milk takes its time coming in. This is called delayed onset of lactation, and it happens to nearly 1 in 3 new moms.

Common Reasons

• Long or stressful labor
• C-section birth
• Blood loss during delivery
• Health issues like diabetes or thyroid imbalance
• Not breastfeeding or expressing often enough in the first few days

What You Can Do

• Hand express colostrum every couple of hours, even if just a few drops
• Nurse or pump at least 8 times in 24 hours
• Use skin-to-skin time to help your hormones do their thing
• Work with a lactation consultant for hands-on help

Your body can catch up, even after a slow start.

What’s Actually in Breast Milk (And Why It’s Always Changing)

Your breast milk is constantly adapting—literally changing composition based on your baby’s age, time of day, and even the length of the feeding.

Early on, you produce colostrum, which is rich in antibodies and immune support. Then comes mature milk, a perfect blend of:

• Water
• Carbs (mainly lactose)
• Fats
• Proteins
• Vitamins and minerals
• Enzymes and live cells

How Milk Changes Over Time

• Fat levels increase to meet your baby’s growing energy needs
• Milk made in the morning is often more plentiful, while evening milk tends to be richer in fat
• Preterm babies get milk tailored to their development needs

Your milk also passes on your immune protection, helping protect your baby from illness and supporting gut health.

If You’re Struggling, You’re Not Failing

Breast milk production isn’t all instinct. It’s part science, part skill, and a whole lot of trial and error. If you’re struggling, it doesn’t mean you’re doing anything wrong.

Here’s What Matters

• Keep offering the breast often
• Get help early if you’re in pain or unsure (IBCLCs are a great resource)
• Combo feeding is still breastfeeding—any amount of breast milk has benefits
• Take care of your mental health.

You’ve got this.

Resources

• The stages of lactation
• Find a breastfeeding support group near you.
• Milkology Breastfeeding Class – Affordable, video-based online course to help you master breastfeeding at your own pace.

References

• Physiology, Lactation — StatPearls, NCBI Bookshelf (2023). Covers the roles of prolactin and oxytocin, stages, and how breastfeeding is hormonally and behaviorally regulated. Great for explaining “how it all starts.
• Genetic and Physiological Factors Affecting Human Milk Production and Composition — Nutrients (2020). Gives an in-depth look at what influences milk volume and content, including maternal health, hormones, and genetics.
• Anatomy and Physiology of the Breast During Pregnancy and Lactation — PubMed (2020). Breaks down breast anatomy, hormonal shifts pre- and post-birth, and timelines for colostrum and mature milk production.