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Curious about what's happening to allow breastfeeding? This article explains how you’ll produce breastmilk and how your breastmilk adapts and changes.

How do my breasts produce milk?

As soon as you're pregnant, your body starts to change to support milk-making. You may notice some of these changes in your breasts, like a slight tenderness and maybe a darkening of your nipples and areola. These changes are among the early signs of pregnancy (NHS Choices, 2016b).

Mammary glands

These glands are in your breasts and produce breastmilk. Each mammary gland contains the following parts that help you to make breastmilk (MIDIRS, 2011).


These are small clusters of sacs that develop when you are pregnant and produce your breastmilk (Sternlicht et al, 2006). Muscles that squeeze the milk into ductules surround these sacs.


These are small channels carrying milk from the alveoli to the milk ducts.

Milk ducts

These are the network of channels delivering milk from the alveoli and ductules to your baby. When you’re pregnant, these ducts grow larger and there will be more of them. The average breast has about nine milk ducts ready for breastfeeding (Geddes, 2007).

When will I start making milk?

During pregnancy your breasts increase in size as the mammary glands grow to support milk production. Sometime during the second trimester your body is ready to produce milk. You might notice a little milk leaking from your breasts in the final weeks of pregnancy (WHO, 2009).

Once your baby is born and you pass the placenta, your body releases the hormone prolactin. This tells your body to produce milk (WHO, 2009).

"You can start to feed your baby immediately after birth as soon as you’re both ready."

Skin-to-skin contact can help to stimulate your milk flow and your baby’s natural feeding responses (NHS Choices, 2016b).

What is colostrum?

Colostrum is the first milk your breasts produce in the few days following birth. It is thick and golden yellow in colour (NHS Choices, 2016b). Colostrum is very concentrated and full of vitamins and antibodies. All of this helps your baby grow and fight off infections (NHS Choices, 2016b). It also helps expel meconium – the black, sticky poo babies are born with (NHS Choices, 2016b).

Your baby will only need about a teaspoonful at each feed because colostrum is so concentrated. To begin with your baby may want to feed often, perhaps every hour. They'll begin to have fewer, longer feeds after a few days. The more you breastfeed, the more your baby's sucking will stimulate your supply and the more milk you'll make.

After a few days the colostrum will be replaced by more mature milk, which is more liquid and greater in volume (WHO, 2009). Approximately two to four days after birth you may notice your breasts are warmer and fuller feeling; this is known as your milk coming in (NHS Choices, 2016b).

The let-down reflex

When your baby starts sucking at your breast, this releases the hormone oxytocin, causing the tiny muscle cells around the alveoli to contract and squeeze out breastmilk. This squeezing is known as the let-down reflex (WHO, 2009; NHS Choices, 2016b). Some women get a tingling feeling, which can be quite strong, while others don’t feel anything. Both are normal.

You may notice your baby respond when your milk ‘lets down’. Their quick sucks will change to deep rhythmic swallows as the milk begins to flow. Babies often pause after the initial quick sucks, while they wait for more milk to arrive (NHS Choices, 2016b). There may be a number of let downs every time you breastfeed, which you may or may not be aware of.

You may also feel some contractions in your belly during the first few days of breastfeeding your baby. These are known as afterpains and feel like mild labour contractions. They are caused by oxytocin shrinking your uterus (womb) back to its pre-pregnancy size (WHO, 2009; NHS Choices, 2016b).

Breastfeeding frequency

Mums start producing mature milk as soon as their baby is born. This happens whether their baby is ever placed at their breast or not. You may notice this surge in production as your milk coming in around two to four days after the birth. Your breasts may look and feel fuller than before (NHS Choices, 2016b).

After this, you continue to make milk as a result of milk being removed from your breasts. This happens either as your baby drinks the milk or by you expressing it with your hands or a breast pump (WHO, 2009).

When breastfeeding is going well, this is what drives the milk supply. As milk is removed, your body gets the signal to make more. Your baby will never fully empty your breasts. If your baby feeds a lot, your body increases the milk supply in response (NHS Choices, 2016b).

Young babies typically feed frequently, at least eight times in 24 hours (or more), often in clusters of feeds with small gaps in between. Counting the feeds is not realistic, as you might not know whether your baby is starting a new feed or ending a previous one (NHS Choices, 2016c).

Changes in your breast milk

The fat content of your milk gradually increases as the milk is removed. So when breasts are less full, the fat content is proportionately higher (Martin et al, 2016). Healthy, effectively feeding babies usually get the right milk intake and type of milk for them (Martin et al, 2016).

When your baby seems to have had sufficient on one breast, you can switch sides and offer the other breast. Your baby may show they’ve had enough of one breast by coming off it or slowing right down. Not all babies take both sides each time. Some are happy with one, while other babies show they want three, four or more sides at a session (NHS Choices, 2016c; NHS Choices, 2017).

"Breastmilk constantly changes to meet your baby’s needs. It is responsive to changes in the mother’s diet, bacteria and viruses in the environment and the baby’s feeding behaviours."

Breastmilk content also varies according to the time of day. Evening milk contains more components that relax and aid babies sleep, while daytime milk contains different elements that stimulate activity (Sanchez et al, 2009).

Breastmilk can also change in response to the baby or mother’s illness, with an increase immune cell levels to aid recovery (Riskin et al, 2012). After your child’s first year in the world, the fat and energy content of breastmilk increases to meet their growing needs (Mandel et al, 2005).

Support to help you breastfeed

It can take time for you and your baby to get the hang of breastfeeding. Plenty of help and support is available to help you overcome any challenges. Getting breastfeeding support makes a huge, positive difference.

Contact your local NCT branch or call our Infant Feeding Line on 0300 330 0700 to find out what breastfeeding support is available locally. We have local NCT Breastfeeding Counsellors who can offer a call, virtual visit, or home visit, depending on their availability. You may also have a local drop-in NCT breastfeeding support group. Our breastfeeding support groups are a great place to meet other mums with babies of a similar age. Peer support is really beneficial to new mums.

This page was last reviewed in January 2018.

Further information

NCT supports all parents, however they feed their baby. If you have questions, concerns or need support, you can speak to a breastfeeding counsellor by calling our helpline on 0300 330 0700, whether you are exclusively breastfeeding or using formula milk. Breastfeeding counsellors have had extensive training, will listen without judging or criticising and will offer relevant information and suggestions. You can also find more useful articles here.

You might find attending one of our NCT New Baby courses helpful as they give you the opportunity to explore different approaches to important parenting issues with a qualified group leader and other new parents in your area.

Make friends with other parents-to-be and new parents in your local area for support and friendship by seeing what NCT activities are happening nearby.

Visit our breastfeeding support contacts page.

NHS Choices breastfeeding information.

National Breastfeeding Line (government funded): 0300 100 021.

Geddes DT. (2007) Inside the lactating breast: the latest anatomy research. J Mid Women’s Health 52(6):556-63. Available From: [Accessed January 2018].

Mandel D, Lubetzky R, Dollberg S, Barak S, Mimouni FB. (2005) Fat and Energy Contents of Expressed Human Breast Milk in Prolonged Lactation. Pediatrics. 116(3):e432-e435. Available From: [Accessed 1st January 2018].

Martin CR, Ling PR, Blackburn GL. (2016) Review of Infant Feeding: Key features of breast milk and infant formula. Nutrients. 8(5): 279. Available From: [Accessed 1st January 2018].

NHS Choices. (2016) Signs and Symptoms of Pregnancy. Available from: [Accessed 1st January 2018].

NHS Choices. (2016) Breastfeeding the first few days. Available from: [Accessed 1st January 2018].

NHS Choices. (2016) Breastfeeding: is my baby getting enough milk? Available from: [Accessed 1st January 2018].

NHS Choices. (2017) Your breastfeeding questions answered. Available from: [Accessed 1st January 2018].

Riskin A, Almog M, Peri R, Halasz K, Srugo I, Kessel A. (2012) Changes in immunomodulatory constituents of human milk in response to active infection in the nursing infant. Pediatr Res. 71(2): 220-225. DOI: 10.1038. Available from: [Accessed 1st January 2018].

Sánchez CL, Cubero J, Sánchez J, Chanclón B, Rivero M, Rodríguez AB, Barriga C. (2009) The possible role of human milk nucleotides as sleep inducers. Nutritional Neuroscience. 12 (1):2 DOI: 10.1179/147683009X388922. Available from: [Accessed 1st January 2018].

Sternlicht MD, Kouros-Mehr H, Lu P, Werb Z. (2006). Hormonal and local control of mammary branching morphogenesis. Differentiation 74(7):365-381. Available from: [Accessed 1st January 2018].

WHO. (2009) Infant and Young Child Feeding: Model Chapter for Textbooks for Medical Students and Allied Health Professionals. Geneva: World Health Organization; 2009. SESSION 2, The physiological basis of breastfeeding. Available from: [Accessed 1st January 2018].

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