How milk production works

Mothers have successfully breastfed their children for thousands of years of human history without understanding how it works. It’s a bit like driving a car – as long as it’s working well, you don’t need to know what’s going on under the bonnet!

If you are having breastfeeding problems, such as low milk supply or too much milk, or are wondering why your baby’s feeding pattern is different from what you expected, it can help to understand more about the science of lactation (producing milk).

Most of the research that has ever been done on breastfeeding has been done in the last few years. It’s a very exciting time! Lots of things that experienced mothers have always known turn out to have a clear basis in the anatomy of the breast and the science of milk production, for example:

• each baby and mother pair is different,
• healthy, full term babies are the best judges of when and how long to feed, and
• to make more milk, remove more milk.

Getting ready – the developing breast

Your breasts start preparing for milk production from puberty. From then on, they grow a little with each menstrual cycle. Inside the breast, the branches and buds that will become milk ducts and alveoli (milk storage sacs) start to develop. Radiation or trauma to the chest at this stage can have an impact on later breast development. (1)

Lactation begins – pregnancy

Breast tenderness is common in early pregnancy – a sign that the breast is completing its development. Milk production begins in the middle trimester, so if a pregnancy ends after about 15-16 weeks, colostrum (early milk) will be present. Some people choose to express colostrum in the last few weeks of pregnancy. 

Find out about our free Beginning Breastfeeding online course.

Lactation takes off! The first few days

During pregnancy, milk production is held in check by the hormone progesterone, produced by the placenta. Once the baby is born and the placenta leaves your body, levels of progesterone drop quickly. This drop in progesterone, combined with high levels of the milk-making hormone prolactin, allows lactation to begin fully a few days after birth.

In the first few days after birth, your breasts are still producing colostrum. It’s sometimes called ‘liquid gold’, for its rich colour and its unique importance for your baby’s health. Colostrum acts like a protective shield for your baby. It lines their gut to help keep germs out, boosts their immature immune system, and gives them a unique mix of growth factors, hormones, and live immune cells that no formula can match. (2) Ask any farmer – they’ll tell you that baby animals thrive when they get their mother’s colostrum!

The supply of colostrum is controlled by hormones, not demand. The amount increases each day, but it remains limited in quantity. If you’re still nursing an older child when your new baby is born (tandem feeding), it’s a good idea to make sure your newborn feeds first during these early days. The small quantity and thick texture of colostrum give your baby a chance to practise feeding before they have to manage larger volumes. You can read about how to make sure your baby is deeply and comfortably attached at the breast and feeding effectively here.

You can read more about quantities of colostrum in ‘How much milk?’ below.

As your milk increases rapidly, by three to five days after birth you might notice:

• breast tenderness
• warmth
• discomfort
• swelling
• increase in breast size, 
• and maybe a mild fever.

This increase can happen a bit later for first-time mothers, or after caesarean birth. (3)

Engorged (swollen) breasts?

The discomfort you feel is mostly due to extra fluid and blood flow triggered by the increase in milk volumes. Don’t panic – your breasts won’t feel like this for long! As your breasts adjust to making the amount of milk your baby needs, the swelling will settle down. If nursing your baby or expressing some milk doesn’t quickly help you feel more comfortable, there are other steps you can take.

Milk slow to increase?

Retained placental fragments can reduce or even stop milk production. If you have unexplained low milk production and are still bleeding heavily or irregularly after you would expect to have stopped, check with your midwifery team or doctor. Removal of the last fragments of placenta will usually allow milk production to resume normally.

You may have heard that overweight or obesity (a higher BMI, especially over 30) can lead to breastfeeding problems. It is not clear whether having a higher BMI, by itself, is a problem for breastfeeding – many larger women breastfeed easily. Some conditions associated with obesity, such as diabetes and insulin resistance, may delay your milk ‘coming in’ (increasing in volume) in the early days after birth. (4)

Supply and demand (day 3-5 onwards)

Until day 3-5, milk production is controlled entirely by hormones and will happen automatically, whether or not you go on to breastfeed. Around day 3-5, the system switches to a different mode. Milk will only continue to be made if milk is removed from your breasts. The more milk that is removed, the more milk will be made. This enables your body to adapt to the number of babies you have. With enough milk removal, it is possible to exclusively breastfeed twins or triplets! If you don’t breastfeed or express milk at all, your milk production will gradually shut down over about two weeks.

Remove milk early

The amount of milk that is removed in the early days and weeks after birth is important for later milk production. (5, 6) This is the ideal time to build your milk supply, by breastfeeding or expressing.

Remove milk often

After their first feed and a few hours of sleep, full-term, healthy newborn babies feed frequently, around the clock. Most babies need to feed at least 8-12 times in 24 hours in the early weeks. (7) If your baby is not feeding as often as this yet, or is not feeding efficiently, it is important to express your milk, if your goal is a full milk supply.

Breasts that are well drained make milk quickly. As milk builds up in the breast, milk production begins to slow down. If you are trying to maximise milk production, it’s important not to wait until your breasts feel full before nursing or expressing. Over time, this will reduce milk production. (8)

Milk supply challenges

Most of us can make more than enough milk for our babies. But some things can make it harder.

If your baby has any risk factors for not being able to feed effectively, such as being:

• premature,
• small for gestational age,
• unwell
• jaundiced,
• very sleepy, or
• separated from you

then early, frequent milk expression will help to ensure plenty of milk to meet their needs, now and later. You can see a useful video here about how to get started.

If you have any risk factors for low milk supply, you can give your milk production the best possible start by removing milk early and often in the hours and days after birth.

Risk factors include:

• previous history of low milk production
• previous breast radiation or surgery
• polycystic ovary syndrome (PCOS)
• thyroid problems (hypo- or hyper-)
• a history of infertility with hormonal cause
• unevenly sized, widely spaced breasts, with little or no changes during or after pregnancy,
• obesity (BMI over 30). (9, 10)

Even if you have one or more of these risk factors, you may still be able to make a full milk supply – you never know what you can do until you try! If you are not able to produce all the milk your baby needs, you can still enjoy a close, happy feeding relationship with your baby. You can read about how to use donor breastmilk or formula to support breastfeeding here.

Mothers who need to supplement with donor milk or formula early on are often able to cut back – or stop altogether – once their baby is eating family foods (solids). Many continue to breastfeed for months or years.

Getting back on track after a difficult start

Milk production settles to a stable level by about a month after birth, with most of the increase in the first two weeks. After that, it can be harder to boost supply. That’s why it’s important to get feeding support early if there are signs your baby isn’t getting enough milk, such as if your baby:

• does not poo every day (in the first 4-6 weeks)
• has pink crystals (urates) in their nappy after the third day
• is not doing yellow poo by the fifth day
• loses more than 7-10% of their birth weight by the fifth day
• loses weight after the fifth day, or
• does not regain their birth weight by 10-14 days.

An LLL Leader or breastfeeding specialist can help you understand what might be causing the issue, make sure your baby is fed safely, and support you in protecting your milk supply. If enough milk isn’t being removed, your production may not increase to meet your baby’s needs. Expressing can help maintain your supply while you work on any feeding challenges. If the problem is with milk production, your breastfeeding supporter can help you make a plan to maximise your milk supply. You’ll need to stay in close contact with your baby’s healthcare providers to monitor their growth and wellbeing.

You can read more about what to do if you’ve had a difficult start in Getting back on track – the ‘3 Keeps.

Common questions 

My breasts feel much softer, or my baby is pooing less – has my milk disappeared?

We often hear this around a month or so after birth. There’s no need to panic – milk can’t suddenly vanish, unless you take certain medications (including some contraceptives and decongestants), or become pregnant again. Breast ‘deflation’ – which can happen very suddenly! – is a sign that your breasts are getting used to making milk. The swelling that made your breasts feel full, tender, and uncomfortable in the early days and weeks has settled down now. From now on your breasts will probably feel normal most of the time, unless for some reason you have a longer gap between feeds. If your baby has been growing well on your milk up to now, softer breasts are no reason to worry. 

Maybe your breasts never really felt full, or still feel full a lot of the time? That’s normal too, as long as your baby is growing well. If uncomfortable breasts are a problem, talk to a breastfeeding helper.

Many babies start to poo less often after the first 4 – 6 weeks, and that’s normal, as long as everything else is okay. It’s a sign that their digestive system is maturing. Some babies continue to poo several times a day well beyond six weeks, while others may only poo once a day, or even less. Every baby is different. 

Lack of poo can sometimes be a sign that something else is going on, such as inefficient breastfeeding, low milk production, or problems with digesting milk. Keep an eye on your baby’s weight gain, at least until they’ve got a solid track record of steady growth. Your health visiting team can advise on how often to weigh your baby. If your baby often seems uncomfortable, or nursing feels difficult for either of you, seek help from a breastfeeding supporter. If you have any concerns about your baby’s health, talk to your health visiting team or GP.

Why is my baby feeding so often (or feeding less often)?

Most new parents are surprised by how often and intensely their newborn wants to breastfeed. They need to feed frequently to fuel their growth and bring in plenty of milk for the months to come. Nursing also calms and comforts them while they get used to being in the world. As long as it’s comfortable for both of you and your baby is growing well, you can be confident that your baby is just doing what they need to do. You can read more about the intense early weeks here.

 After the first month or so, when most babies need to breastfeed at least 8–12 times in 24 hours, your baby will start to settle into their own rhythm. This might be similar to the early weeks, or very different. Their pattern may also be unlike other babies the same age. Perhaps your friend’s baby nurses for half an hour at a time with long breaks in between, while yours still prefers frequent feeds throughout the day and night. Why such a difference? Should your baby be more like hers?

Part of it may be your baby’s ‘style’ – some people like to linger over their food! But the biggest reason comes down to how your breasts work.

The idea of breast storage capacity is a relatively new finding from breastfeeding research. Your storage capacity is the amount of milk that your breasts can hold between feeds, which can vary a lot between individuals. (11) It helps explain why a ‘one-size-fits-all’ approach to breastfeeding doesn’t work.

To understand storage capacity, let’s assume that:

Alisha and Beth both have three month old babies and well established milk supplies.

Alisha’s breasts can hold 75ml of milk and Beth’s breasts can hold 150ml of milk.

Both their babies need about 750ml of milk per day (this is an average amount – some babies take less, and some take more than this).

Alisha’s baby needs to feed at least 10 times in 24 hours to get 750ml of milk.

Beth’s baby could get the same amount of milk in only five or six feeds. (Feeding only five or six times in 24 hours is not common – it’s at one end of a wide range of feeding patterns!)

Both babies are getting as much milk as they need and are growing well, but they have very different feeding patterns. 

What happens if Alisha and Beth are told that their babies ‘should’ both be feeding eight times in 24 hours?

Alisha’s baby is hungry and miserable. She is no longer getting enough milk, so her growth slows down. If this continues, Alisha’s milk production will also slow down, because her full, uncomfortable breasts act like a brake on her milk production. If this goes on for a long time, it might be hard for Alisha to increase her milk production again later.

Beth’s baby is irritable because his mother keeps trying to feed him again when he doesn’t want any more milk! 

Both babies can grow well and enjoy breastfeeding – as long as their mother follows their lead and lets them find their own feeding pattern.

Alisha has less flexibility in her feeding patterns because if she doesn’t feed often enough, her breasts become overfull and she doesn’t have room to make more milk. To grow well, her baby needs to feed frequently day and night, and needs to nurse on both breasts at most feeds.

Beth, with her larger storage capacity, has more flexibility in her feeding patterns. Her baby is likely to have fewer feeds per day than Alisha’s, and is more likely only to take one breast per feed. Beth can also choose to feed more often, if her baby wants to, or if her breasts are uncomfortable.

It is important to ensure frequent feeding during the early weeks, when milk production is becoming established. Most newborns need to feed at least 8-12 times in 24 hours. After the early weeks, most babies start to spend less total time feeding, as they become more efficient. Some babies will also choose to have fewer feeds. 

Most mothers never need to worry or even think about their breast storage capacity, because their babies are brilliant at working it out! Full-term, healthy babies are able to choose their own feeding pattern that works with their mother’s breasts and their own needs as they grow. (12) If your baby is growing well and seems content, their feeding pattern is just right – even if it’s different from other babies their age.

How much milk do I need to make?

In the first three days after birth, volumes of colostrum are small, but just right for a baby who is able to nurse frequently around the clock. (13, 14) 

The amount of colostrum increases quickly, more or less doubling every day in the first few days. If you need to express in the first 24 hours after birth, you might use a syringe or teaspoon to catch drops. A day or two later, a syringe or teaspoon won’t hold enough milk. By the fourth day after birth, a baby may take around 60ml (2oz, or about four tablespoons) or more at each feed. 

If you are expressing your milk, for example, because your baby was born early, it can help to know how much to aim for. Researchers have come up with slightly different figures, but a reasonable goal is 650 – 750ml in 24 hours by 2-3 weeks after birth (15, 16)

A premature or small-for-dates baby might not need this much milk yet, but aiming for a full supply now means you will have enough to satisfy them for the rest of their breastfeeding time.

Milk production remains stable from one to six months, with little increase after one month. (17) After the baby starts eating family foods (solids) around six months of age, milk production starts to reduce, as milk is gradually replaced by other foods in the baby’s diet. If you are making as much milk as your baby needs at one month, you will keep on doing so, as long as:

• your baby keeps on removing enough milk,
• you don’t get pregnant, and
• you avoid medications that can affect milk production. Birth control methods that contain progesterone may reduce milk production in some women. (18)

How does milk production work if I’m feeding two (or more)?

Most of us are capable of producing enough milk for twins or more, as long as the babies feed effectively and we respond to their cues about how often and how long they need to nurse. Because multiples are more likely to arrive early, you may need to express milk at first until they’re strong enough to manage all their feeding themselves.

See our articles on premature and late preterm babies for more information.

How about if you’re nursing two children of different ages (‘tandem nursing’)? If your toddler or preschooler nurses a lot one day and not at all the next, your supply may feel unpredictable. This can be especially tricky if you have a fast milk flow that sometimes overwhelms your baby! You can find tips for helping babies manage a fast flow here — and LLL Leaders are always available to offer support.

What do I need to know about fat in milk (‘foremilk’ and ‘hindmilk’)?

Have you been told to feed for a certain number of minutes per breast, or only on one breast, to ensure your baby ‘gets the hindmilk’? This advice is common – but it’s based on misunderstandings about how breastfeeding works. Here’s what you need to know:

• The breast makes milk fat at a stable level. The types of fat in your milk are somewhat related to the types of fat in your diet, (19) but the amount of fat in your milk is not related to your diet.

• The milk your baby gets at the start of a feed (sometimes called ‘foremilk’) has a lower level of fat than the milk at the end of the feed (‘hindmilk’). 
• As the breast is drained, fat levels in milk increase because more fat droplets are ‘squeezed’ to the front of the breast and out through the nipple.
• The level of the fat at the start of one feed depends on how long it has been since the last feed. The longer the gap between feeds, the lower the level of fat at the start of the next feed. 

The varying amount of fat in milk is not a problem – all the milk is good! Research shows that full-term, healthy babies are experts at balancing their own diets. They will stop feeding when they have had enough calories, adjusting their feeding patterns to the composition of the milk. (20) For most babies, all you need to do is follow their lead. 

The balance of fat in milk can be a problem if:

• the baby is often taken off the breast before they’ve had as much milk as they need – this can happen if you’re trying to feed to a schedule, or
• you have an overwhelming amount of milk (oversupply). In this case, the baby may be growing very fast – their growth curve crosses centiles upwards on the growth chart – and may struggle with the speed of milk flow, coming off the breast gagging, spluttering, and upset. 

In these scenarios, the baby may not get enough fat to slow the milk’s journey through their digestive system. As a result, the milk can pass through too quickly for them to fully digest the lactose (milk sugar). The sugar ferments in the gut, producing green, frothy, explosive poo (or, less commonly, constipation), flatulence (farting) and severe discomfort. If this describes your baby, an LLL Leader can help. A baby who does yellow poo and is comfortable does not have any problem with the balance of milk in their diet. 

A baby who isn’t growing well because of a breastfeeding problem needs more milk overall, not just more fat. As well as getting help with breastfeeding, if your baby is growing slowly it’s important to get them checked by a doctor to rule out underlying health problems.

You can read more about fat levels in milk here.

How milk changes over time

If you are expressing your milk, you will be able to see the change from sticky, transparent, yellow or orange colostrum to thinner, white or blue-ish ‘mature milk’ by about the fourth day after birth. The composition of your milk is changing to adapt to your baby’s need for more energy. The milk of mothers who give birth prematurely is initially different from the milk of mothers who give birth at full term, to meet the extra needs of their babies. (21)

If you’re nursing two children of different ages (‘tandem nursing’), your milk will be geared to the stage of your younger child, because your breasts ‘reset’ with each new pregnancy. Your older child might have loose stools in the second half of your pregnancy and for a few days after the birth of their sibling – colostrum has laxative properties, to help clear out the new baby’s bowels! 

Your milk changes from hour to hour, day to day, week to week for as long as you breastfeed or express. It responds to your baby’s stage of development, any illnesses you or your baby (and any older children you’re also breastfeeding) are in contact with, and even the time of day or night it was made. (22, 23, 24, 25) 

Beyond the early months

Have you been told that your milk is no longer important for your baby after six months, or 12 months? This is simply not true! Milk is your baby’s main source of protein and calories until about a year of age, and continues to contribute to the child’s health and nutrition through the second year and beyond. The World Health Organization and other health authorities recognise this by recommending at least two years of breastfeeding, if possible. (26, 27)

Your milk adapts to meet your baby’s needs as they grow. For example:

• over time, levels of the antibacterial enzyme lysozyme increase in milk, protecting your baby as they put foods and other objects in their mouth. (28)
• as the total amount of milk begins to decrease gradually, from about six months, levels of key immune factors such as immunoglobulins increase, so that the child receives about the same amount each day, even though they take less milk. (29)
• Levels of fat, protein and energy in milk are higher in the second year than in the first year of breastfeeding. (30, 31)

Lactation ends – involution

Milk production is at its most vulnerable in the early days after birth – your body quickly shuts it down if milk removal stops. As the weeks and months go by, milk production becomes much more settled and robust. Milk will continue to be made for as long as milk is removed. Mothers returning to work after six months, for example, can be confident that their milk supply will adapt to variations in their daily and weekly schedules, even if they work shifts or need to travel away overnight. By this stage, it’s much easier to breastfeed ‘part time’, if necessary. Your milk won’t decrease in a hurry, even if it’s used less than usual for a few days. Many breastfeeding toddlers and older children spend time away overnight with a non-resident parent, or grandparents, and continue breastfeeding when they are with their mother. You just need to keep your breasts comfortable during this time – unlike in the early days of breastfeeding, you don’t need to keep your supply high by expressing as much as the child would have drunk. Toddlers, preschoolers, or older children may nurse just once a day, or every few days, as breastfeeding winds down.

It’s reckoned to take around 40 days for the breast to reach complete ‘involution’ (a non-lactating state) after the end of breastfeeding or milk expression. Some mothers find that they leak or can express drops of milk months or even years after their last feed. If the amount of milk is large, or you start making milk again after a gap even though you are not pregnant, check with your doctor. Spontaneous milk secretion (galactorrhoea) can be a side effect of some medications, or a sign of hormonal dysfunction.

When children are able to wean from the breast at their own pace, weaning often takes place over months and years. The most common time for children to choose to stop breastfeeding is between their second and third birthdays. (32) Milk production reduces gradually and, by the time the child has their final feed, may have dwindled to almost nothing. 

Summary

• From puberty onwards, your breasts are getting ready to feed a baby.
• Milk production starts by the middle of pregnancy, driven by hormones.
• From day 3-5 after birth, milk production is driven by milk removal.
• Healthy, full term babies are the best judges of when and how long to feed.
• Each baby and mother pair is different.
• To make more milk, remove more milk. 
• If you have any problems with milk production, work with a breastfeeding helper – the earlier the better. 
• Milk changes day to day, month to month, and year to year to meet your child’s needs.
• Milk production becomes more settled and robust over time. It becomes easier to breastfeed part-time if you need to be away from your child.
• Your milk continues to benefit your child for as long as you breastfeed.

Written by Jayne Joyce, LLL Oxfordshire and Karla Napier, LLL Edinburgh, 2021.

Updated October 2025. 

Review date: October 2027.

Further reading

References

1.  Lo, Andrea C et al. “Breast Hypoplasia and Decreased Lactation From Radiation Therapy in Survivors of Pediatric Malignancy: A PENTEC Comprehensive Review.” International journal of radiation oncology, biology, physics vol. 119,2 (2024): 549-559. doi:10.1016/j.ijrobp.2021.08.032 

Available at https://www.redjournal.org/article/S0360-3016(21)02725-5/abstract (accessed 13 October 2025).

2. Garofoli, Francesca et al. “Anti-Inflammatory and Anti-Allergic Properties of Colostrum from Mothers of Full-Term and Preterm Babies: The Importance of Maternal Lactation in the First Days.” Nutrients vol. 15,19 4249. 2 Oct. 2023, doi:10.3390/nu15194249 Avauilable at https://www.mdpi.com/2072-6643/15/19/4249 (accessed 13 October 2025).

3. Li, Sen et al. “Factors Influencing Delayed Onset of Lactogenesis: A Scoping Review.” International journal of general medicine vol. 17 2311-2326. 21 May. 2024, doi:10.2147/IJGM.S452108

Available at https://pmc.ncbi.nlm.nih.gov/articles/PMC11127660/ (accessed 13 October 2025).

4. Peng, Yijuan et al. “Incidence and factors influencing delayed onset of lactation: a systematic review and meta-analysis.” International breastfeeding journal vol. 19,1 59. 22 Aug. 2024, doi:10.1186/s13006-024-00666-5 

Available at https://internationalbreastfeedingjournal.biomedcentral.com/articles/10.1186/s13006-024-00666-5 (accessed 13 October 2025).

5. Kent, Jacqueline C et al. “Breastmilk Production in the First 4 Weeks after Birth of Term Infants.” Nutrients vol. 8,12 756. 25 Nov. 2016, doi:10.3390/nu8120756

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6. Levene, Ilana et al. “The relationship of early expressed milk quantity and later full breastmilk feeding after very preterm birth: A cohort study.” Maternal & child nutrition vol. 21,1 (2025): e13719. doi:10.1111/mcn.13719

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