Health conditions

Lactose intolerance in babies

What is lactose intolerance?

Lactose intolerance is a condition when your body can’t break down a carbohydrate (sugar) called lactose which is present in cow’s milk, human breast milk, or any other milk from a mammal. 

What causes lactose intolerance?

Lactose intolerance occurs when the lining of the intestine (bowel and gut) has been damaged. This damage is commonly caused by diarrhoea infected with viruses, such as the rotavirus.

Babies with lactose intolerance cannot digest lactose properly and it remains indigestible in the stomach. The build up of the lactose sugar attracts water which produces watery faeces (poo) causing diarrhoea.

The type of diarrhoea associated with lactose intolerance often causes sore, broken skin around the baby’s bottom. You may also notice your baby’s stomach makes loud noises. Other symptoms include passing wind and crying when passing faeces.

Can breastfed babies be lactose intolerant?

Yes. Babies can be lactose intolerant because they drink human milk and baby formulas containing lactose.

Very young babies often don’t produce enough of the enzyme (lactase) which helps to digest lactose. Your baby may still have lactose intolerance without ever having had infectious diarrhoea.

Breastfed babies often have quite loose faeces so it is important that they are tested and diagnosed before any lactose-free diet is trialled.

Your doctor will discuss a plan for you and your baby and you still may be able to continue breastfeeding. 

If your doctor advises you to stop breastfeeding it is usually only for a very short time, so you will need to take steps to keep up your milk supply.

Signs and symptoms

Symptoms may include:

  • pain and swelling in the tummy
  • crankiness
  • failure to settle at feeding times, coming on and off the breast
  • failure to gain weight
  • diarrhoea
  • bulky, frothy and watery faeces
  • red bottom with skin worn away in places.

How is lactose intolerance diagnosed?

The baby’s faeces will be tested for sugar. While the test is simple it can sometimes be difficult to collect a sample. The samples can be collected at a doctor’s surgery or hospital. 

If your baby has had rotavirus or another type of infectious diarrhoea the recurrence may indicate your baby has lactose intolerance.

If you think your baby is lactose intolerant, see your doctor.

Treatment of lactose intolerance

Your baby will be given lactose-free formula for 1 to 4 weeks prescribed by your doctor.

If your baby is old enough to eat solids it is important they don’t eat food high in milk content, such as ice-cream, yoghurt, soft cheese and custard, or drink sweetened drinks including fruit juice or cordial.


Regrading is the process of reintroducing your baby’s normal milk feeding cycle.

Your baby may take between 5 and 7 days to adjust and return to their normal milk feeding cycle. Sometimes a doctor or a nurse may advise you to regrade in a shorter period of time. When regrading is complete, foods containing milk can be reintroduced.

Regrading guide for young babies

Replace one bottle of lactose-free milk with one bottle of usual milk each day for 5 days, until all lactose-free bottles have been replaced by usual milk bottles, as shown below. If your baby develops diarrhoea, go back one step. If it persists see your doctor.

Day one:

  • 1 x usual milk
  • 4 x lactose-free milk.

Day two:

  • 2 x usual milk
  • 3 x lactose-free milk.

Day three:

  • 3 x usual milk
  • 2 x lactose-free milk.

Day four:

  • 4 x usual milk
  • 1 x lactose-free milk.

Day five:

  • 4 x usual milk.

Where to get help

  • See your doctor.
  • Speak to a child health nurse.
  • Visit a GP after hours.
  • Ring healthdirect Australia on 1800 022 222.


  • Lactose intolerance is the reduced ability to digest milk sugars, due to insufficient amounts of the gut enzyme called lactase.
  • Breastfed babies can be lactose intolerant, because lactose is found in human milk as well as baby formula.
  • Diarrhoea can be a symptom of lactose intolerance in babies.

Child and Adolescent Health Service

This publication is provided for education and information purposes only. It is not a substitute for professional medical care. Information about a therapy, service, product or treatment does not imply endorsement and is not intended to replace advice from your healthcare professional. Readers should note that over time currency and completeness of the information may change. All users should seek advice from a qualified healthcare professional for a diagnosis and answers to their medical questions.

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