Lactose Intolerance in Infants and Children: A Guide for Healthcare Professionals

Summary: Lactose intolerance is an intolerance (not an allergy) to the sugar lactose in milk. Very rare in infants and children as their gut has good amounts of lactase enzyme, it usually occurs secondary to other causes and resolves after a few weeks. It is managed by dietary exclusion and then gradual reintroduction. Lactase drops or capsules with meals may help. Adequate calcium and vitamin D intake is important until the condition improves. 

Lactose is a carbohydrate found in the milk of most mammals. It is a disaccharide sugar and is the main source of calories in milk. It provides 40% of the total energy in breast milk. 

Lactose is important for adequate growth and development of an infant. It also helps with micronutrient absorption like calcium and iron and keeps babies’ guts healthy. (1, 2) It is the main sugar found in human and (most) mammalian milk and requires the presence of lactase for its digestion. 

Lactose is broken down into glucose and galactose by lactase enzyme.

The lactase enzyme breaks down lactose into glucose and galactose. Babies and children have this enzyme in abundance in their small intestinal lining, specifically inside the brush border enterocytes. 

What is Lactose Intolerance? 


Lactose intolerance arises from the absence or insufficiency of lactase enzyme in the lining cells of the small intestine. This leads to inadequate digestion and absorption of lactose in the colon. 

Note lactose intolerance is different from cow’s milk allergy. 


Lactase enzyme production is steeply declining globally. Most adults have low or no lactase enzymes and therefore are lactose intolerant to some extent. (3, 4

According to the World Population Review, lactose intolerance is most common in Asia, and especially in East Asian countries. 80% of Hispanic/ Latino adults and 90% of Asian adults are affected as their lactase levels decrease after weaning. In contrast, only 15-20% of Northwestern Europeans are affected since they produce lactase throughout life. 

The UK has some of the lowest lactose intolerance rates in the world, with only 8% of the population living with this condition. People of Asian or Afro-Caribbean descent make up most of this demographic.

Types of Lactose Intolerance

The main types of lactose intolerance are (5): 

  • Primary Lactose intolerance
  • Secondary lactose intolerance
  • Congenital Lactose intolerance
  • Developmental lactose intolerance

Primary Lactose intolerance

As children grow into adults, lactase enzyme production goes down leading to worsening lactose intolerance over time. This is called primary lactose intolerance.

Secondary Lactose Intolerance

This develops secondary to damage to the lining of the small intestine which can be from injury or conditions like gastroenteritis, coeliac disease, and inflammatory bowel disease. Secondary lactose intolerance is temporary and usually resolves once the underlying condition is managed appropriately. 

Congenital Lactose Intolerance

Babies can be born with congenital lactase deficiency or alactasia. If lactose is not immediately eliminated from their diet, it can lead to severe diarrhoea which, if left untreated, can lead to dehydration and faltering weight. A lactose-free formula should be started as soon as the condition is suspected.  

Developmental Lactose Intolerance

Babies born before the 37th week of gestation can develop lactose intolerance temporarily. As they grow their gut matures and they are able to digest lactose normally.  


Without lactase, lactose cannot be digested and absorbed in the small intestine. The resulting high concentration of lactose pulls fluid into the gut, causing watery diarrhoea. The lactose then moves into the colon, where bacterial fermentation produces gases that cause symptoms like abdominal cramping, bloating, and flatulence. These symptoms often produce urgency to open the bowels half to two hours after lactose ingestion.

Symptoms of lactose intolerance if a child drinks lactose containing cow's milk.

Distinguishing Lactose Intolerance from Cow’s Milk Protein Allergy

Cow’s milk protein allergy (CMPA) can be frequently confused with lactose intolerance. Cow’s milk allergy is an allergic reaction to the proteins found in milk, whereas lactose intolerance is an intolerance to lactose sugars in milk. 

Here is a brief overview of the differences between the two (6):

Cow’s milk allergyLactose intolerance
An allergic reaction to proteins in cow’s milkThe inability to digest the milk sugar lactose
Involves the immune systemDoesn’t involve the immune system
Gastrointestinal, skin and respiratory symptoms may be involvedSymptoms are only gastrointestinal, such as diarrhoea. No skin and respiratory symptoms are involved
The tiniest amount of cow’s milk protein could cause an allergic reactionA small amount of lactose can often be tolerated


Infantile colic is an early sign of difficulty in digesting the large quantities of lactose present in breast and standard formula milk. 

After a thorough assessment, a trial of a lactose-free diet is advised for 2-6 weeks followed by the reintroduction of lactose. If the symptoms settle on exclusion and return on reintroduction, this confirms the diagnosis. If there is no change in symptoms upon exclusion of lactose from the diet, then other possible diagnoses are considered. Lactose intolerance for longer than 6-8 weeks is rare in infants and young children, and other diagnoses should be considered if this seems to be the case. 

Exclusion of lactose from a baby’s diet would mean offering them lactose-free formula milk if under 6 months of age. If exclusively breastfed, mothers should be advised to exclude lactose from their diet until symptoms have resolved. 

If over 12 months old and not breastfed, lactose-free cow’s milk can be trialled and is available over the counter. Parents should be supported by a dietitian in following a lactose-free diet for their child and in managing symptoms. 

It is important to advise parents not to exclude dairy products completely but to go for lactose-free options like Lactofree milk, yoghurt and cheese. This is to avoid confusing cow’s milk protein allergy with lactose intolerance and to ensure adequate calcium intake. 

Infants should not be kept on low or lactose- free formulas for longer periods of time. If the diagnosis is unclear, their GP can arrange for a hydrogen breath test. (7)  

Some diagnostic tests used internationally are (8):

  1. Lactose intolerance test: the patient is asked to consume a lactose-containing drink after fasting. Stool lactose content is then examined. 
  2. Hydrogen breath test: ingestion of a lactose-containing drink is followed by measurements of breath hydrogen. High levels after consumption confirm the diagnosis. 
  3. Stool acidity test: levels of lactic acid in the stool can be directly measured. 


Formula or breastfed infants

If there are no symptoms suggestive of cow’s milk allergy, Coleif can help. As Coleif contains lactase enzymes, it can be given for the first few months of life until the gut matures enough to be able to digest lactose. Some comfort formula milks are also available with low lactose content. 

Note soy formula is not suitable for infants under 6 months of age. 

If an infant develops lactose intolerance following gastroenteritis, they can be trialled on a lactose-free formula milk. If breastfed, lactose can be excluded from the maternal diet for 6-8 weeks. Parents should be referred to a dietitian for support regarding lactose-free diet and food labelling

Over 12 months

Infants over 12 months of age with lactose intolerance do not require lactose-free formula milk. They can be offered Lactofree cow’s milk, yoghurts, cheese and butter. They can also be offered plant-based milks like oat, soya, and coconut. Parents should be advised to opt for full-fat, fortified and unsweetened alternatives. 

Rice milk should be avoided until the child is 5 years old; rice milk is high in arsenic that will not be metabolised quickly enough in younger children. It is also low in protein so the child will require supplementation from other sources. 

Lactose Reintroduction 

Lactose should be reintroduced once symptoms have resolved. This should be done gradually starting with low-lactose foods like hard cheese, butter and yoghurt. (9)

Evidence suggests that children and adults with lactose intolerance are able to tolerate 5g of lactose per dose which is equal to about 100ml of whole milk. (10) Up to 12 g of lactose per day can be tolerated if distributed throughout the day and consumed with other foods. Parents should be advised by dietitians to carefully read food and drink labels as some processed foods or other non-dairy foods might contain lactose. There is a list of lactose-rich and low-lactose-containing foods and drinks on the Allergy UK website.

Some medications also contain lactose.   

Lactase Enzyme

Lactase enzymes are available in the market and can be given with foods and drinks containing lactose to help avoid GI symptoms. However, there has not been much research done on the dosage suitable for infants and children. 

Important Nutrient Considerations

Paediatric patients on a lactose-free or low-lactose diet might not be getting enough calcium to meet their requirements. Food diaries can help estimate calcium intake which can be supplemented by other sources if required. 

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Disclaimer: The information provided in these blog posts is intended to support and assist healthcare professionals in expanding their knowledge base and staying informed about the latest advancements in paediatric nutrition. However, this information should not be used as a substitute for your professional clinical judgement. While every effort is made to ensure the accuracy of the information, healthcare professionals should continue to use their discretion in diagnosing and treating health conditions. Always adhere to your local and national clinical guidelines and protocols when providing care. The author is not responsible for any actions taken based on the content of these blog posts.

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