Lactose Intolerance in Babies

Lactose is the main sugar found in breast milk. It is produced in the breast, it doesn’t come from a mother’s diet. Lactose is very important for the normal health and development of human babies. It provides about 40% of a baby’s energy needs, helps with calcium and iron absorption, promotes friendly bacteria Lactobacillus bifidus, keeps pathogenic bacteria in the gut at bay, and is important for development of the large and complex human brain and central nervous system.1

Lactose intolerance in babies

Lactose intolerance is the inability to digest lactose. True lactose intolerance is very rare in babies because breast milk, the biologically normal food, is full of lactose and babies are usually very well adapted to digest it. This article looks at types of lactose intolerance in babies, causes and symptoms of lactose overload and ways to avoid it.

Types of lactose intolerance in babies

Babies are either born with lactose intolerance due to a metabolic disorder (a rare but serious risk to health) or they can get a temporary form of it with several possible causes (much less serious). Different names are used for the different types of lactose intolerance and these vary slightly between authors.

#1 True lactose intolerance

(also called primary or congenital lactose intolerance)

A specific enzyme called lactase breaks lactose down into glucose and galactose (more sugars). It is produced in tiny folds (called brush borders) in the lining of a baby’s intestine. There are a few rare metabolic disorders that mean a baby doesn’t produce enough of this enzyme. True lactose intolerance is very rare, but when present it will be diagnosed within a few days of birth due to the severe and serious symptoms like vomiting, diarrhoea, jaundice and failure to thrive.2 Your health professionals will advise on a special diet for your baby.

#2 Lactose overload

(also called secondary or temporary lactose intolerance.)

If there is too much lactose in the gut for the enzyme (lactase) to break down; symptoms of wind (gas), tummy ache and copious frothy green or watery stools may be seen. Linda Palmer explains:

Lactose may come in faster than baby’s available amounts of lactose digesting enzyme, lactase, can respond. In this case, some of the lactose can sit undigested in the bowel, causing water to rush in to dilute the sugar, leading to loose stools, and allowing bacteria to ferment it, which causes smelly gas. Over time this situation can keep the intestines irritated and cause a little bleeding. Such chronic irritation can cause a drop in lactase enzyme production. This can create a vicious cycle.

Lactose overload is much more common than “true” lactose intolerance. The rest of this article discusses causes, symptoms and remedies for this type of temporary lactose intolerance in babies.

Is lactose intolerance the same as cows’ milk allergy?

No. Having a reaction to traces of cows’ milk protein that enter breast milk via the mother’s diet is not the same as lactose intolerance or lactose overload. However an ongoing food allergy can damage the lining of the gut where the enzyme needed to digest lactose is produced, causing symptoms of lactose overload. Lactose overload and cows’ milk allergy can therefore both be present at the same time.

Eliminating lactose from a mother’s diet won’t help a baby’s symptoms of lactose overload because lactose is added to breast milk in the breast. However, if the real issue is sensitivity to cows’ milk protein; avoiding foods with lactose probably will help the symptoms because cows’ milk proteins and lactose tend to be found in the same foods.

What causes lactose overload?

Anything that prevents lactose being digested properly in the intestines can cause lactose overload. Possibilities include (1) damage to the special cells that produce the enzyme in the intestine, (2) if the volume of low fat breast milk passing through the intestines overwhelms the available enzyme or (3) immaturity.

#1 Damage to the intestinal lining

If there is any damage to the intestinal lining it can affect the production of the enzyme lactase which is produced in the delicate brush borders of the baby’s intestines. Types of damage include inflammation (e.g. irritation from cows’ milk allergy or gluten), bacterial or viral infection (e.g. gastroenteritis) or antibiotic use. Other possible causes of damage include partially digested formula, parasites, and some mothers notice a connection with live vaccines such as rotavirus.3 If there is not enough enzyme, large amounts of lactose can pass undigested to the lower bowel. Here it will be fermented by bacteria giving the familiar symptoms of gas, discomfort and lots of green watery stools.

Damage to the brush borders may take some time to heal. Pharmacist and breastfeeding specialist Wendy Jones says:

Average recovery time for the gut of a baby with severe gastroenteritis is 4 weeks, but may be up to 8 weeks for a baby under 3 months. For older babies, over about 18 months, recovery may be as rapid as 1 week. Medical advice should be sought for any baby with long-term symptoms and/or who is failing to thrive.

#2 High volume of lower fat milk

A big breast milk feed with a normal lactose content but low fat content can pass through to the lower bowel too quickly for the lactose to be digested properly. This can lead to colic type symptoms of wind (gas), tummy ache and green or watery stools. When breast milk has a higher fat content, it slows the transit time in the bowel, giving time for proper digestion.4 Possible causes for an excess of low fat milk tend to be connected to breast storage capacity and how often a baby changes breasts while breastfeeding. A lactose overload is more likely for a mother who has excess breast milk or who tends to stop a feed before a baby has finished draining one breast. An IBCLC lactation consultant can help you identify how to avoid this type of lactose overload, and see:

#3 Immaturity

Some premature babies might not produce enough lactase until they mature. This is known as developmental lactase deficiency.5

What causes lactose intolerance in adults? In many cultures across the world, levels of the enzyme lactase start to fall after three to seven years of age (to correspond with weaning). They often fall so low (particularly in non-Caucasian groups) that an individual may become lactose intolerant (unable to digest lactose). This may not happen until adulthood and will affect consumption of cows’ milk products with lactose.  This is not the same as lactose intolerance in babies.6. Author Nancy Mohrbacher reserves the name primary lactose intolerance for this adult type (Mohrbacher. 2020. p 301)


baby looking uncomfortable on mother's shoulder
Lactose overload may give symptoms of wind (gas), tummy ache and copious frothy green or watery stools

Symptoms of lactose overload in babies

Good weight gain but windy, unsettled, lots of poop

A baby with lactose overload might typically gain weight very well but show several of the following colic type symptoms:

  • Flatulence. Note that swallowing of air during a feed is not thought to be a cause of a baby’s flatulence or colic symptoms as excess air is burped out through the mouth.78
  • Loads of explosive green or yellow frothy, foamy or watery poop. Note: there can be several other causes of green poop too.
  • Tummy ache or “colic”
  • Unhappy, unsettled baby
  • Nappy rash
  • Mucousy poop

Where milk allergy is the underlying cause other symptoms may be present as well see Milk Allergy in Babies.

Poor weight gain is possible

Not all babies continue to gain weight well and some may even fail to thrive as the milk is passing through the gut too quickly to be digested and absorbed;

Some babies lose so much weight from the rapid passage of all food that they fail to thrive, although the mother often has a booming milk supply from all the stimulation, needing breast pads to mop up leakage.

Blood in the stools?

Constant irritation to the intestines may also give rise to small amounts of bleeding in the stools (Palmer, 2015).

Evening colic

Some breastfed babies seem to have colic type symptoms every evening at a set time but are quite cheerful the rest of the day or night. Author Maureen Minchin hypothesises that this could be due to  “lactose overload” from the first feed in the morning i.e. when there is a lot of low fat, lactose rich breast milk on a relatively empty tummy (Milk Matters, 2015).

Mother reclining and looking at her baby feeding
Lactose is the main sugar in breast milk, it is made in the breast and does not come from the mother’s diet

How to avoid lactose overload

Finding the reason for lactose overload and knowing what to do about it will usually improve the symptoms without needing to stop breastfeeding. A breastfeeding specialist such as an IBCLC lactation consultant will be able to review breastfeeding factors that can affect lactose overload such as a baby’s positioning (how they are held at the breast), latch (how your baby is attached to the breast) and breastfeeding management. Additional tips to consider include:

Finish the first breast, offer the second

The fat content of breast milk increases during a feed and also increases the closer together the feeds are. If a mother is shortening feeds (perhaps because of painful nipples) or feeding on a schedule this could lower the fat content in breast milk. Less fat reduces the time spent in the stomach (gastric clearance time) resulting in the lactose passing through the stomach and bowel without being properly digested (Noble & Bovey, 1998). Finishing the first breast before offering the second side will help your baby to get the proportion of higher fat milk he needs.

Stay on one breast per feed if needed

If a mother has a very large storage capacity she may only need to feed from one breast per feed so that her baby can get a good balance of higher fat milk. Jack Newman explains (with a caution!):

In some situations where the baby is colicky from getting too much milk too quickly, and fixing the latch and finishing one side before offering the other breast does not work, it may be worthwhile to try giving one breast at a feeding or even two feedings in a row. The mother needs to be aware that this may cause her milk production to decrease, and that the baby may fuss because he’s not getting as much milk as he wants—even if he is still gaining weight well.

Breast compressions

Some authors suggest trying breast compressions and breast massage to help to mix the fat content of breast milk and release more higher fat milk.910

Be flexible

Feeding plans such as block feeding (staying on one breast per feed or for a set period of time) need to be flexible and not “rules”. Just because a baby wants one breast in a morning may not be the case by the evening when he might need both breasts per feed. Similarly what works at two months of age to cure fussy behaviour may need changing in a few weeks time or during a growth spurt. See One Breast or Two per Feed? for more information.

Is food allergy the cause?

The underlying cause of difficulty digesting lactose could be an allergy or intolerance to cows’ milk protein. Even if your baby is not eating solids they might be sensitive to cows’ milk proteins present in breast milk via your diet. Over time a sensitivity may cause inflammation and irritation to baby’s gastrointestinal tract causing the symptoms of lactose overload. For further information see Milk Allergy in Babies and Elimination Diet for further reading.

Not enough milk?

An unhappy baby with scant green nappies may not be getting enough milk rather than the problem being milk allergy or lactose overload. Sometimes a fussy baby who seems to want to feed a lot is just “hanging out” at the breast but not getting enough milk. Advice to stay on one breast per feed or for several feeds is not appropriate here. Your IBCLC can help you decide what is going on and see How to Make More Breast Milk for lots of ideas to increase your milk supply. Jack Newman points out on his Facebook page:

Many babies diagnosed with “allergy” to something in the milk get better when put on special formulas. Why? Not because they are no longer exposed to the mother’s milk, but rather because now the baby gets more milk.

Mother’s diet

Lactose is produced in the breast, and the amount of lactose containing foods a mother eats won’t make any difference to the lactose content in breast milk. However maternal diet can be important:

  • If there is inadequate fat in the mother’s diet this can make lactose overload worse for baby ( Noble and Bovey, 1998). See Best Breastfeeding Diet and Foods to Avoid for more information about fats in a nursing mother’s diet.
  • If a baby is sensitive to cows’ milk protein (in breast milk via mother’s diet) this may cause inflammation and irritation to baby’s gastrointestinal tract which can then cause symptoms of lactose overload. See Elimination Diet for more information.

Lactase drops

Author Linda Palmer says that drops containing the enzyme lactase can be used to predigest lactose in expressed milk (Palmer, 2015 p142).

Continue to breastfeed

A baby with an irritated intestine will really benefit from the anti inflammatory effects of breast milk so it’s important to continue breastfeeding whenever possible (Palmer, 2015, p 141).

My doctor said I should stop breastfeeding

Some doctors are confused about temporary lactose intolerance, milk allergy and colic. They may recommend lactose-free formula or newer “special” formulas instead of breast milk. However the answer to most cases of temporary lactose intolerance is to get help with breastfeeding rather than switch to industrial formulas. A baby with an irritated intestine needs the anti inflammatory effects of breast milk and a breastfeeding specialist can help suggest changes to feeding management11.

it is sinister that artificial baby milks, however specialised are promoted as being superior milks for allergic babies. It is even more insidious to hear such messages reiterated by paediatric specialists working with these children and their families. p46

…formulas are

  • concentrated sources of the problem proteins
  • without the advantage of having been processed by maternal digestion
  • utterly devoid of the other benefits bestowed by her milk. p47
Mother breastfeeding on a sofa looking at her baby
A breastfeeding specialist can help to identify causes of lactose overload

My doctor says tests confirm my baby has lactose intolerance

Some doctors might diagnose lactose intolerance if they measure excess acid (reducing sugars) in a baby’s poop or hydrogen gas in a baby’s breath due to temporary lactose intolerance (Palmer, 2015, p 141). Noble and Bovey state that the presence of reducing sugars in a baby’s poop can be quite normal for breastfed babies particularly under six weeks of age12 while the Australian Breastfeeding Association says both a hydrogen breath test and a test for reducing sugars in the stool are often positive in normal breastfed babies under three months of age13. James Akre explains:

It is usual to find reducing substances such as sugars in the stools of healthy breast-fed infants; they contribute to maintaining the acid environment that retards the growth of pathogens. In contrast, the delayed gut transit time of industrially prepared milks permits almost total metabolism of these sugars.


Lactose is the main sugar in breast milk. It is made in the breast and does not come from the mother’s diet. It is very rare for a baby to be truly intolerant to lactose. However there can be times when there is so much lactose it is difficult for the baby to digest. This is often called a lactose overload and, when undigested in the gut, lactose gets broken down or fermented by bacteria to give gas, discomfort and lots of frothy or foamy watery poop. A food allergy can be a cause of symptoms of lactose overload as can certain breastfeeding management regimes. An IBCLC lactation consultant can help identify causes and work with you to help avoid a baby getting symptoms of lactose overload.