What Causes Low Milk Supply? The Most Common Reasons and What Can Be Done

Advice
Written By Bobbi Daly

In the first post in this series, I looked at the difference between perceived low milk supply and actual low milk supply, and explained that the only two reliable indicators are weight gain and nappy output. If you have not read that post yet, it is worth starting there.

This post is for mothers where supply genuinely is low. Understanding why is not just interesting — it is essential. The cause determines the approach. A supply problem rooted in latch and feeding management needs a completely different response to one rooted in hormonal factors or breast anatomy. Getting the right support means getting the right assessment first.

Two Types of Low Milk Supply

Low milk supply is generally divided into two categories:

Demand-side causes — things that reduce the signal to make milk. These are by far the most common. They include problems with latch, feeding frequency, milk transfer, and feeding management. In most cases, when supply is low, this is where the problem lies — and these causes are often addressable with the right support.

Supply-side causes — things that affect the breast's underlying capacity to produce milk, regardless of how often or how well the baby feeds. These are less common but real, and they include hormonal conditions, breast anatomy, previous surgery, and certain medications.

Many mothers have a combination of both. And in some cases, what begins as a demand-side problem — a poor latch that is never properly assessed — gradually becomes a supply-side problem as the breast receives insufficient stimulation over weeks or months.

Demand-Side Causes — The Most Common Reasons Supply Is Low

Latch and Milk Transfer Problems

This is the most common cause of low milk supply. A baby who is not latching deeply and effectively is not draining the breast well. When the breast is not drained, the body reads this as a signal to make less milk.

A baby can appear to be feeding — attached to the breast, feeding for long stretches — and still not be transferring milk efficiently. Position and latch matter, but what ultimately matters is whether milk is being removed. Signs that transfer may be poor include slow weight gain, infrequent dirty nappies in the early weeks, a baby who feeds very frequently without ever seeming settled, and a mother whose breasts never feel drained.

Getting a full feeding assessment — not just a quick latch check — is essential when supply is a concern.

Infrequent Feeding or Missed Feeds

Milk production works on a supply and demand basis. The more frequently and effectively milk is removed from the breast, the more milk the body produces. Conversely, when feeds are missed, delayed, or replaced — by formula top-ups, a dummy, or long stretches between feeds — the breast receives fewer signals to produce milk and output falls.

In the early weeks in particular, feeding frequency is one of the most important drivers of supply. Newborns need to feed at least eight to twelve times in twenty-four hours. Any practice that reduces this — scheduled feeding, long gaps overnight, or supplementing without expressing to compensate — can affect supply.

Formula Top-Ups Without Expressing

When formula is added without expressing to replace the missed breast stimulation, supply falls. This is one of the most common ways a downward spiral begins — supply drops, more formula is needed, supply drops further. It does not mean formula should never be used, but when it is used alongside breastfeeding, expressing to maintain supply is important unless you are intentionally moving towards combination feeding.

Tongue Tie

A tongue tie that affects function — not just one that is visible — can significantly affect a baby's ability to drain the breast effectively. The result is poor milk transfer and, over time, reduced supply. Tongue tie is not always identified at newborn checks, and not every tongue tie causes feeding problems. But when latch is consistently poor despite good positioning and support, tongue function is always worth assessing.

A Sleepy or Unwell Baby

A baby who is very sleepy — whether due to jaundice, illness, medications used during birth, or prematurity — may not feed frequently or effectively enough to maintain supply in the early days. This is a recognised cause of supply difficulties in the newborn period and one that benefits from early, proactive support.

Nipple Shields Used Without Support

Nipple shields can be a useful tool in certain situations, but when used without proper guidance they can reduce the stimulation the breast receives and affect supply over time. If you are using nipple shields, it is worth getting a full assessment to ensure they are being used appropriately and that supply is being maintained.

Supply-Side Causes — Less Common but Important to Know About

Insufficient Glandular Tissue

Some mothers have breasts that did not develop enough milk-producing glandular tissue during puberty or pregnancy. This is sometimes called hypoplastic breast tissue or insufficient glandular tissue (IGT). It does not always correlate with breast size — some mothers with small breasts have plenty of glandular tissue, and some with larger breasts have less than expected.

Signs that may suggest IGT include breasts that did not change much during pregnancy, widely spaced breasts, or tubular breast shape — though none of these is diagnostic on its own. Mothers with IGT can often breastfeed partially, and even a small amount of breast milk is valuable. Getting support from an IBCLC who understands this condition is important.

Hormonal Conditions

Several hormonal conditions can affect milk production:

Thyroid disorders — both underactive and overactive thyroid can affect supply. If you have a known thyroid condition, it is worth ensuring it is well managed during the breastfeeding period.

Polycystic ovary syndrome (PCOS) — associated with insulin resistance, which can affect prolactin levels and delay the onset of full milk production. Some mothers with PCOS breastfeed without difficulty; others find supply is affected.

Retained placenta — a fragment of retained placenta after birth can maintain high progesterone levels, which suppresses milk production. If milk is very slow to come in after birth, this is one cause worth ruling out with your GP or obstetrician.

Insulin resistance and type 2 diabetes — both are associated with delayed onset of milk production and lower supply. This is an area of growing research interest.

Previous Breast Surgery

Breast reduction surgery carries the highest risk of affecting milk supply, as it may involve removal of glandular tissue and division of milk ducts. Breast augmentation carries a lower risk, though it depends on the surgical approach. Biopsy or other breast surgery may also affect supply depending on the location and extent of the procedure.

Many mothers who have had breast surgery breastfeed successfully, often with support. It is worth discussing your surgical history with an IBCLC antenatally so that you can plan appropriately and monitor supply closely in the early days.

Certain Medications

Some medications can reduce milk supply. These include combined hormonal contraceptives (the combined pill, the contraceptive patch, and some hormonal coils), some decongestants containing pseudoephedrine, and medications that lower prolactin. If you are concerned about a medication you are taking, speak to your GP — and always check with a reliable source such as the Breastfeeding Network's Drugs in Breastmilk service before stopping any prescribed medication.

Previous Breast Irradiation

Radiotherapy to the chest or breast area can affect glandular tissue and milk production. If you have a history of chest radiotherapy, it is worth discussing this with your GP and an IBCLC before or after your baby is born.

Why Getting the Right Assessment Matters

The most important thing to take from this post is that low milk supply is not one problem with one solution. It is a range of different problems with different causes — and the right response depends entirely on understanding what is actually happening.

A mother whose supply is low because of a latch problem and infrequent feeding needs skilled breastfeeding support. A mother whose supply is low because of IGT or a hormonal condition needs a different kind of assessment and realistic, honest information about what is achievable. Both deserve proper support — not generic advice to feed more often, and not premature reassurance that everything is fine.

If supply is genuinely a concern, getting a full assessment from an IBCLC — not just a quick check — is the right first step.

In the next post in this series, I will look at what actually helps to increase milk supply, what the evidence says, and why most of what you will find online is not supported by good research.

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Bobbi Daly
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How to Increase Milk Supply: What Actually Works and What Doesn't
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Do I Have Low Milk Supply? How to Tell the Difference Between Real and Perceived Low Supply