Lactose intolerance in babies is often misunderstood. Here’s what you need to know.
There are many myths about lactose intolerance and babies, which can make feeding decisions confusing. Most babies can digest lactose, the natural sugar in breastmilk, without any trouble. Understanding how lactose works and what signs to look for can help you feel confident about feeding your baby.
Key points about lactose
- Lactose is the sugar found in all mammal milks. It’s made in the breast and the amount in your breastmilk doesn’t change based on what you eat.
- Lactose levels stay the same throughout a feed. The milk your baby gets at the start and end of a breastfeed has about the same amount of lactose. However, the milk at the end of a feed contains more fat, which helps keep your baby satisfied.
- Lactase is the enzyme needed to digest lactose. If a person doesn’t produce enough lactase, they can’t digest lactose properly. This is when lactose intolerance occurs.
Types of lactose intolerance in babies
Primary (Congenital) Lactose Intolerance
This is an extremely rare genetic condition. Babies are born without any lactase enzymes, so they can’t digest lactose at all. From birth, these babies don’t gain weight and show clear signs of malabsorption and dehydration. This is a medical emergency, and they need a special diet and urgent care straight away.
Secondary Lactose Intolerance
Secondary lactose intolerance happens when something damages the lining of your baby’s gut, such as a tummy bug, food allergy, or another illness. rotavirus gastroenteritis, parasitic disease (Giardia lamblia), intestinal disease due to cow’s milk protein allergy, celiac disease, Crohn’s disease, AIDS, malnutrition or lack of absorption surface, as in the case of short bowel syndrome
The damage reduces the amount of lactase enzyme, making it harder for your baby to digest lactose for a while.
Symptoms can include loose, frothy stools and irritability. The good news is that secondary lactose intolerance is temporary. Once your baby’s gut heals, your baby can digest lactose normally again, and breastfeeding can usually continue throughout recovery.
Recovery and feeding during secondary lactose intolerance
Secondary lactose intolerance is temporary, as long as your baby’s gut has a chance to heal. If the cause of the gut damage, such as a food allergy, is found and managed (for example, by removing a problem food from your diet), your baby’s gut can recover even while breastfeeding continues.
If your doctor diagnoses lactose intolerance, you can keep breastfeeding as long as your baby is otherwise well and growing normally. In fact, lactose plays an important role in your baby’s development. Human milk contains a high concentration of lactose compared to animal milks because lactose is used to produce human milk oligosaccharides (HMOs), which support gut health and immunity. Lactose also provides galactose, a sugar needed to build components of nerve cell membranes, which are essential for brain growth and development.
Don’t remove lactose from your baby’s diet for more than a short time unless a doctor advises it and is supervising.
What about lactose-free formula?
If your baby has symptoms of lactose intolerance, you may be told to alternate breastfeeding with feeds of lactose-free formula or even take your baby off the breast. But lactose-free formula is only needed for formula-fed babies who are very malnourished or losing weight. Breastmilk is the best food for your baby and will help your baby’s gut heal.
It’s also important to know that some babies are sensitive to cow’s milk or soy protein, which are found in both regular and lactose-free formulas. In some cases, these formulas can make symptoms worse. You should seek professional advice on the need for hypoallergenic formula.
If your baby keeps having symptoms or isn’t growing well, see your doctor for support and guidance.
Common questions and useful information
No. The amount of lactose in your breastmilk isn’t affected by what you eat. Changing your diet won’t change the lactose level in your milk.
It’s rare for a baby to need to stop breastfeeding due to lactose intolerance. Human milk supports gut healing and is the best choice for most babies. If your baby has ongoing symptoms or isn’t thriving, see your doctor for advice.
Doctors may order a ‘hydrogen breath test’ or stool tests. If your baby is lactose intolerant, positive results would be expected. But they are also positive in most normal breastfed babies under three months, so these tests may not be useful.
You may have heard about giving drops containing the enzyme lactase to babies who show symptoms of lactose intolerance. There isn’t much evidence that giving the drops directly to babies is very effective, though some parents report that larger doses might help in certain cases.
Lactase products are mainly designed to be added to expressed breastmilk (or other milk) and left for several hours or overnight, so the enzyme can break down the lactose before feeding. In practice, this method seems to be occasionally useful for some babies. While lactase drops may help reduce symptoms, they do not address the underlying cause of what is damaging your baby’s gut.
No. Lactose intolerance in adults is different from what babies experience. Most babies can keep breastfeeding even if they show symptoms.
Lactase enzyme levels normally change over a person's life span. After birth, babies quickly start making more lactase, but from about 3 to 5 years old, the amount starts to drop, and it falls even more in later childhood. This means many adults make much less lactase and can have trouble digesting lactose.
Cows’ milk is often drunk by adults in some parts of the world, especially by people with northern European backgrounds. In about 70% of people worldwide, including many Australians, the amount of lactase drops so much in adulthood that they become lactose intolerant. This is mostly due to genetics. People with Asian, African, Australian Aboriginal, or Hispanic backgrounds are more likely to be lactose intolerant as adults. People with European backgrounds are more likely to keep making lactase and can often drink milk as adults.
Even adults with very low lactase can sometimes handle small amounts of lactose because the normal bacteria in their gut help break it down. Still, they may get loose stools and wind after having dairy foods.
Human milk has a lot of lactose – more than cow’s milk or milk from other animals. This is because babies need it for their rapid growth and development. Removing lactose from a baby’s diet for more than a short time should only be done with medical advice and supervision.
Other conditions with similar symptoms
If your baby has symptoms like liquid, green, frothy stools and irritability, it’s important to know that these can be caused by several different conditions—not just lactose intolerance.
Lactose overload can look very similar to lactose intolerance and is often mistaken for it. You might want to check information on lactose overload to see if it matches what you’re seeing in your baby. Many mums find that addressing lactose overload first helps relieve their baby’s symptoms. Lactose overload in babies
Food allergies and intolerances can also make babies unsettled. Foods your baby is allergic or intolerant to can pass through your breastmilk. Sometimes, removing a specific food (like cows’ milk protein) from your diet can help, but it’s important to get advice from a dietitian to identify the problem foods and make sure your diet stays healthy for both you and your baby. Breastfeeding your baby with food sensitivities
Cows' milk protein allergy or intolerance is often confused with lactose intolerance, but they are not the same thing. The confusion happens because both lactose and cows’ milk protein are found in dairy products. In some cases, allergy or intolerance to a food protein can cause secondary lactose intolerance, so a baby may have both at the same time.
If you’re unsure what’s causing your baby’s symptoms, talk to your health professional for guidance.
It’s rare for a baby to have to stop breastfeeding
As explained above, there are several types of lactose intolerance, but it's very rare for a baby to have to stop breastfeeding because of this condition. Except for the extremely rare primary type, there is always a cause behind lactose intolerance in babies. Getting to the cause and fixing that is the key to resolving your baby's symptoms.
Based on original article by Joy Anderson AM BSc(Nutrition), PostgradDipDiet, IBCLC (retired), ABA Breastfeeding Counsellor
© Australian Breastfeeding Association December 2025
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