Lactation (Human Milk Production): Causes & How It Works (2023)


Lactation (Human Milk Production): Causes & How It Works (1)

What is lactation?

Lactation is the process of producing and releasing milk from the mammary glands in your breasts. Lactation begins in pregnancy when hormonal changes signal the mammary glands to make milk in preparation for the birth of your baby. It’s also possible to induce lactation without a pregnancy using the same hormones that your body makes during pregnancy. Lactation ends once your body stops producing milk.

Feeding your baby directly from your breasts is called breastfeeding (or sometimes chestfeeding) or nursing. You can also feed your baby milk that you have expressed or pumped from your breast and saved in a bottle.

Where does human milk come from?

Human milk comes from your mammary glands inside your breasts. These glands have several parts that work together to produce and secrete milk:

  • Alveoli: These tiny, grape-like sacs produce and store milk. A cluster of alveoli is called lobules, and each lobule connects to a lobe.
  • Milk ducts: Each lobe connects to a milk duct. You can have up to 20 lobes, with one milk duct for every lobe. Milk ducts carry milk from the lobules of alveoli to your nipples.
  • Areola: The dark area surrounding your nipple, which has sensitive nerve endings that lets your body know when to release milk. To release milk, the entire areola needs stimulation.
  • Nipple: Your nipple contains several tiny pores (up to about 20) that secrete milk. Nerves on your nipple respond to suckling (either by a baby, your hands or a breast pump). This stimulation tells your brain to release milk from the alveoli through the milk ducts and out of your nipple.

It helps to think of the lactation system as a large tree. Your nipple is the trunk of the tree. The milk ducts are the branches. The leaves are the alveoli.

Why do people lactate?

The primary reason people lactate is to feed a baby. Lactation is a biological, hormonal response that occurs during and after pregnancy to feed a newborn baby. Your body triggers specific hormones to initiate milk production and ejection (releasing of milk). All mammals lactate for this purpose and it’s possible to induce lactation in men and in non-pregnant women using the right hormone medications.


What triggers lactation?

A series of hormonal events, which begin when you’re pregnant, trigger the lactation process. That process is called lactogenesis.

Stage one lactogenesis: This begins around the 16th week of pregnancy and lasts until a few days after you give birth.

  • Estrogen and progesterone rise and cause your milk ducts to grow in number and size. This causes your breasts to become fuller. Your mammary glands begin to prepare for milk production.
  • Your nipples darken and your areolas become larger.
  • Your Montgomery glands (small bumps on the areola) secrete oil to lubricate your nipple.
  • Your body begins making colostrum. It’s highly nutritious and filling and serves as your baby’s first milk.

Stage two lactogenesis: This stage starts about two or three days postpartum (after giving birth). It’s when milk production intensifies.

  • Once your baby and placenta are delivered, a sudden drop in your estrogen and progesterone causes the hormone prolactin to take over.
  • Prolactin is the hormone that produces milk.
  • You’ll notice your milk production increases dramatically at this stage. It’s often referred to as milk “coming in.”
  • Your breasts are often engorged (or overly full of milk) to the point where they feel sore, painful or tender.

Stage three lactogenesis: This describes the rest of the time you lactate.

  • Lactation generally continues as long as milk is removed from your breast.
  • The more milk that’s removed, the more milk your body makes to replace it. Frequent feeding or pumping will cause your body to make more milk.

Hormones for lactation

The hormone prolactin controls the amount of milk you produce, and your body begins producing prolactin early in pregnancy. At first, the high levels of estrogen, progesterone and other pregnancy hormones suppress prolactin. Once you deliver the placenta, those pregnancy hormones drop and prolactin takes charge.

When your baby suckles, it stimulates nerves that tell your body to release prolactin and oxytocin. Prolactin causes the alveoli to make milk and oxytocin causes muscle contractions that push out of the alveoli and through the milk ducts.

When milk is released, it’s called a “letdown,” and it takes about 30 seconds of suckling before the letdown occurs. Because you can’t control which breast receives the hormones, the letdown can cause milk to drip from both nipples.

Inducing lactation in people who aren’t pregnant requires medication that mimics hormones your body makes during pregnancy. Suckling from the nipple can initiate lactation, either with a breast pump or by a baby. This is a complex process that involves working closely with a healthcare provider who understands the needs of non-pregnant people and has experience initiating lactation.

When do you lactate during pregnancy?

Lactation begins as early as a few weeks into the second trimester of your pregnancy. As estrogen and progesterone levels rise, your body prepares for lactation by increasing the number of milk ducts in your breasts, and those milk ducts will transport milk from the alveoli to your nipples. About midway through pregnancy, your body creates colostrum, which is your baby’s first milk.

Can you lactate when you’re not pregnant?

Yes, it’s possible to lactate if you’re not pregnant. Inducing lactation is a complex process that usually involves using hormone-mimicking drugs for several months to produce milk. The second part of lactation is expressing the milk through your nipple. Stimulation from infant suckling, pumping with a breast pump or hand-expressing signals the brain to release the milk. It’s common for people in this situation to receive assistance from a healthcare provider who understands the needs of non-pregnant people and has experience initiating lactation.

(Video) Physiology of Lactation Animation

How do you stop lactation?

There are many reasons why you might need to stop producing milk, and you can stop lactating either naturally or with the help of hormonal drugs.

Natural milk suppression

Lactation is a supply-and-demand process. Your milk supply gradually goes down as your baby relies less on breast milk, or as you reduce the number of times you nurse or pump. Generally, if you decrease the volume of milk removed from your breasts, your body will slow milk production.

Suppressing your milk can feel uncomfortable and most people will become engorged (the term for overfilled breasts). You may also leak milk or develop a clogged milk duct. However, you can treat that pain by taking an over-the-counter pain reliever, wearing a firm bra or using an ice pack on your breasts.

Medication suppression

Medications can also be an option if you need to stop producing milk. Your healthcare provider can explain more about lactation-suppressing drugs, as well as the benefits and possible side effects.

(Video) Breastfeeding | 3D Animation


Where are the mammary glands located?

Mammary glands are commonly called breasts and both genders have them. They are located on your chest and are composed of connective tissue, fat and special glandular tissue that makes milk. A woman’s glandular tissue is slightly different because it contains the alveoli and lobules necessary for producing milk. Women also have much more glandular tissue.

Conditions and Disorders

What are common conditions that affect your ability to lactate?

The ability to lactate and the length of time you’re able to produce milk varies. Some can produce milk for years, while others have trouble producing enough milk for their baby.

Some common factors that can impact lactation or breastfeeding are:

  • Hormonal levels and conditions.
  • Medications.
  • Undergoing radiation therapy in the past.
  • Trauma to your breast or nipples.
  • Breast augmentation, reconstruction or other breast surgeries.
  • Other medical conditions like HIV infection.
  • Use of drugs and alcohol.

If you’re nursing or pumping your milk to bottle-feed your baby, you should always consult with your healthcare provider before starting any new medications or treatments. Many medications can pass to your baby through breast milk, which may have dangerous effects on your baby.

What is lactational amenorrhea?

Lactation amenorrhea (ah-men-oh-re-uh) means you aren’t menstruating (getting a period) due to lactation. When you’re lactating, your body produces prolactin, the hormone that produces milk. Prolactin reduces the amount of luteinizing hormone (LH) in your body, which helps trigger the release of an egg during ovulation. If you aren’t producing enough LH, you can’t ovulate or get your period. The length of time you can be amenorrheic due to lactation varies from a few months or until you’re completely done lactating.

Does lactation reduce my risk of any diseases?

Studies have shown that breastfeeding reduces a woman’s risk of ovarian and breast cancers. It can also lower your risk for Type 2 diabetes and high blood pressure.

(Video) Breast anatomy and lactation | Reproductive system physiology | NCLEX-RN | Khan Academy


How do you maintain milk production?

Maintaining lactation is mostly based on supply and demand. The more your baby breastfeeds or the more milk you express with a breast pump, the more your body will make. There are ways to suppress lactation with hormones or oral contraceptives. If you wish to maintain lactation, some things you should do are:

(Video) Human Physiology - Lactation

  • Continue nursing on-demand or pump milk frequently (approximately every four hours).
  • Eat a healthy diet with enough calories. Low-calorie diets can decrease milk supply.
  • Drink plenty of water to stay hydrated. Human milk is primarily water.
  • Avoid smoking, drugs or alcohol. These can reduce your supply and transfer to your milk.

Frequently Asked Questions

What is the difference between lactation and colostrum?

Lactation describes the process of making and secreting milk from your breast. Colostrum is the first milk your breasts create during lactation and the first milk your baby drinks. It’s thick, yellow and commonly called “liquid gold.” Colostrum is high in protein, minerals, vitamins and antibodies.

What is hormone therapy for inducing lactation?

Couples or families who wish to induce lactation, maybe because of adoption, surrogacy or other reasons, can try hormone therapy. Induced lactation means you’re creating a milk supply without being pregnant. It’s a process that involves taking estrogen and progesterone for several months to make your body believe it’s pregnant. This helps prepare your breasts for lactation. Some medications and herbs are believed to help establish a milk supply, too.

Several weeks before your baby arrives, begin pumping your breasts with a breast pump. This encourages your body to release prolactin, which produces milk. Ideally, you express your milk several times a day, just like you would if you had a baby. This helps establish a supply. You can also freeze any milk you produce for use once your baby arrives.

If you’re considering this as an option, you should talk to your healthcare provider about your desire to feed your baby with human milk. Induced lactation works for many people, but not all.

A note from Cleveland Clinic

If you want to feed your baby human milk, it’s helpful to understand the process of lactation so you know what to expect. Talk to your healthcare provider about how to best prepare for nursing or expressing milk. Remember, lactation can look different for everyone depending on your circumstances and health history. If you struggle with lactation at any point, you may feel embarrassed or even ashamed. But struggling with lactation is very common, and lactation specialists and other healthcare providers can help you as you try to overcome these difficulties.

(Video) The science of milk - Jonathan J. O'Sullivan


What is the lactation process in humans? ›

Lactation is the process of milk secretion from the mammary glands of a mother soon after childbirth. The milk, thus produced provides nutrition and immunity to the young one. Galactopoiesis is the stage that maintains milk production and requires prolactin and oxytocin.

What are the 4 stages of lactation? ›

The hormonal control of lactation can be described in relation to five major stages in the development of the mammary gland. (1) embryogenesis; (2) mammogenesis or mammary growth; (3) Lactogenesis or initiation of milk secretion; (4) lactation or full milk secretion; and (5) involution when the infant is weaned.

What causes lactation without pregnancy? ›

Excessive breast stimulation, medication side effects or disorders of the pituitary gland all may contribute to galactorrhea. Often, galactorrhea results from increased levels of prolactin, the hormone that stimulates milk production. Sometimes, the cause of galactorrhea can't be determined.

What stimulates the milk production? ›

Prolactin. Prolactin is necessary for the secretion of milk by the cells of the alveoli. The level of prolactin in the blood increases markedly during pregnancy, and stimulates the growth and development of the mammary tissue, in preparation for the production of milk (19).

What causes lactation? ›

Once your baby and placenta are delivered, a sudden drop in your estrogen and progesterone causes the hormone prolactin to take over. Prolactin is the hormone that produces milk. You'll notice your milk production increases dramatically at this stage. It's often referred to as milk “coming in.”

What are the 3 stages of lactation? ›

The Basics of Breastfeeding

Breast milk has three different and distinct stages: colostrum, transitional milk, and mature milk.

How do I stimulate my breast for lactation? ›

Increasing Your Milk Supply
  1. Breastfeed every time your baby is hungry. ...
  2. Make sure your baby is latching well.
  3. Offer both breasts at each feeding. ...
  4. Empty your breasts at each feeding. ...
  5. Avoid bottles and pacifiers in the early weeks. ...
  6. Get plenty of sleep, and eat a healthy diet.
  7. Pump or express your milk. ...
  8. Relax and massage.

How long does milk supply last? ›

Some people may stop producing over just a few days. For others, it may take several weeks for their milk to dry up completely. It's also possible to experience let-down sensations or leaking for months after suppressing lactation. Weaning gradually is recommended, but it may not always be feasible.

How long is lactation period? ›

The World Health Organization (WHO) recommends exclusive breastfeeding for the first 6 months of an infant's life followed by the addition of nutritionally adequate and safe complementary foods while breastfeeding continues for up to 2 years of age or beyond 3.

Can you breastfeed if you weren't pregnant? ›

It is possible to establish milk production for an adopted baby, even if you have never been pregnant or given birth. The amount of milk you may produce depends on many factors. Most mothers are able to produce at least a little milk.

Does arousal help milk production? ›

Oxytocin released during sexual orgasm is also responsible for letdown when breastfeeding and it is not uncommon to leak or squirt breastmilk when sexually aroused. [2] Prolactin, which increases in order to produce breastmilk, can cause a decrease in libido.

At what age do breasts start lactating? ›

Milk production generally begins around the midpoint of pregnancy, somewhere between weeks 16 and 22.

How does breast milk taste like? ›

Breast milk tastes like milk, but probably a different kind than the store-bought one you're used to. The most popular description is “heavily sweetened almond milk.” The flavor is affected by what each mom eats and the time of day. Here's what some moms, who've tasted it, also say it tastes like: cucumbers.

Can breast milk come back after drying up? ›

It's called re-lactation. It's possible for the female body to come back from “drying up” and produce milk again. In fact, many mothers of adopted children are able to pump and use several methods in order to stimulate their bodies to produce milk, even if they haven't given birth!

What is the fastest way to induce lactation? ›

As stated above, the primary way to induce lactation is through breast emptying: breastfeeding, pumping, or hand expression. The effectiveness of these physical techniques can be enhanced with the use of galactogogues: medications, herbs and homeopathic remedies that support the production of milk.

How can husband help to increase milk supply? ›

It's easy to worry about your partner producing enough milk for your little one, but do your best to relax.
5 lessons to share with your breastfeeding wife:
  1. Feed your baby on demand. ...
  2. Relax. ...
  3. Eat well. ...
  4. Drink plenty of fluids. ...
  5. Contact a lactation consultant.

What snacks help produce breast milk? ›

Nuts or Trail Mix

Try trail mix to combine savory with a little sweetness. Some dried fruits are considered galactagogues, making them especially helpful in lactation, including apricots, dates, and figs. Just grab a handful for the perfect snack serving.

How do you know when your breasts are empty? ›

How do I know whether my breasts are empty? There's no test or way to know for sure. In general, though, if you gently shake your breasts and they feel mostly soft and you don't feel the heaviness of milk sitting in them, you're probably fine.

How much milk can a woman produce per day? ›

Mothers who exclusively breastfeed twins or triplets can produce 2,000 to 3,000 g/day, although this involves nursing an average of 15 or more times per day (Saint et al., 1986). Women who express surplus milk for a milk bank have been shown to produce as much as 3,000 g/day (Macy et al., 1930).

Is it weird to breastfeed someone else's baby? ›

You're watching

Question: Is it OK to breastfeed someone else's baby or child? Answer: No. Absolutely not — even if they have given permission.

How long does it take to induce lactation? ›

How long does it take to induce lactation? If you're interested, you should talk to your doctor and start the process well before the arrival of the baby. Milk production can take weeks to begin—an average of 4 weeks—after you start pumping. The stress of the adoption process can also disrupt the production of milk.

What do surrogates do with breast milk? ›

Pump Milk for the Intended Parents

Then, they will use the milk to either feed their baby through bottles or in combination with their own breastmilk through a supplemental nursing system. You will not be required to pump milk for intended parents unless you are comfortable doing so.

Does breast milking feel good? ›

One woman, who had experienced engorgement, said that she almost felt euphoric after a while when she got the milk flowing. (The baby's suck stimulates the release of the hormones oxytocin and prolactin in the mother. It is oxytocin that is responsible for the let-down reflex and the feeling of relaxation.

How long do human females lactate? ›

After 1-2 years, the production gradually ceases. Production of milk in the breast is a process that hormone levels influence during and after pregnancy. A woman's ability to breastfeed can rely upon many factors. For the most part, breastmilk production depends on loss of milk to provide more (supply and demand).

How long does human lactation last? ›

The World Health Organization (WHO) recommends exclusive breastfeeding for the first 6 months of an infant's life followed by the addition of nutritionally adequate and safe complementary foods while breastfeeding continues for up to 2 years of age or beyond 3.

How long can a woman produce milk? ›

Once your body has begun producing milk, it can continue to do so indefinitely, provided that demand continues (meaning that you have a baby to feed or pump your breast milk). It is common for children to be breastfed for several years before weaning in many countries.

Can breasts still produce milk after a year? ›

Galactorrhea (guh-LACK-toe-REE-uh) is milk discharge from the breast that is unrelated to breastfeeding or that happens at least one year after stopping breastfeeding. It usually happens in both breasts, but it can also happen in only one. Both women and men can have galactorrhea.

Can you induce lactation without hormones? ›

The only necessary component to induce lactation—the official term for making milk without pregnancy and birth—is to stimulate and drain the breasts. That stimulation or emptying can happen with baby breastfeeding, with an electric breast pump, or using a variety of manual techniques.

Can a woman lactate from pleasure? ›

When a woman is lactating, she may have a milk ejection reflex when she experiences orgasm. This response depends on the timing of the sexual encounter, the mother's breastfeeding experience, and the age of the baby.

Can you still lactate after 3 years? ›

It's not unusual for milky discharge to continue for up to two to three years after discontinuing breastfeeding and it typically affects both breasts.


1. Breast Stem Cells (2010) Etsuko Uno
2. BREAST MILK PRODUCTION | How Is Breast Milk Produced | How Does Breastfeeding Works
(Prenatal Yini)
3. How does breast milk formed in the body : How milk is made in woman : Mammary glands milk production
(Amazing World)
4. How does breast milk production work?
(Breastfeeding Magic with Nadiya Dragan)
5. Breastfeeding
(Osmosis from Elsevier)
6. Breastmilk and the difference between Colostrum, Foremilk & Hindmilk - How Breastfeeding Works
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