Updated 30 October

Author: Kathy Beck, APD, Paediatric Allergy Dietitian

Lactose Intolerance or cow’s milk allergy?

If your child develops symptoms after having milk, it can be confusing to work out why. Lactose intolerance and cow’s milk allergy can both cause tummy troubles, but they are different conditions and need different management.

One common misunderstanding is that lactose-free milk or infant formula is suitable for cow’s milk allergy. Lactose-free cow’s milk products still contain milk proteins, so they can still cause an allergic reaction. Understanding this difference helps families choose appropriate foods and avoid unnecessary restrictions.

What is lactose intolerance

Lactose is the natural sugar found in milk, including breastmilk. An enzyme called lactase breaks it down in the small intestine.

When there is not enough lactase, some lactose passes undigested into the large intestine. This can cause:

• Bloating and wind.
• Tummy pain or cramps.
• Loose stools or diarrhoea.

Lactose intolerance is a digestive condition. It does not involve the immune system and does not cause hives, swelling or anaphylaxis. Symptoms often depend on how much lactose is consumed.

The usual inherited form develops as children get older and is uncommon in babies. However, temporary lactose intolerance can occur after gastroenteritis or another condition that affects the lining of the small intestine. It often improves as the gut recovers. Being born unable to digest lactose is extremely rare.

What is cow’s milk allergy

Cow’s milk allergy occurs when the immune system reacts to milk proteins, such as casein and whey. It is most common in infancy and early childhood.

There are two main types:

Immediate IgE mediated allergy

Symptoms usually develop within minutes to two hours of consuming milk. They may include hives, swelling, vomiting or breathing difficulties. Some reactions can progress to anaphylaxis, which is a medical emergency.

Delayed non IgE mediated allergy

Symptoms develop more slowly, often over hours or days, and mainly affect the gut. Depending on the condition, children may have vomiting, diarrhoea, blood or mucus in their stools, feeding difficulties or poor weight gain.

These symptoms can also have other causes. Reflux, unsettled behaviour or changes in stools alone do not confirm milk allergy. A careful assessment helps avoid removing foods unnecessarily.

Some delayed allergies, such as food protein-induced enterocolitis syndrome (FPIES), can cause severe reactions and need specialist care.

The key differences

	Lactose intolerance	Cow’s milk allergy
Trigger	Lactose, the sugar in milk	Proteins in milk
What happens?	Lactose is not fully digested	The immune system reacts to milk proteins
Typical symptoms	Wind, bloating, cramps and diarrhoea	Immediate skin, gut or breathing symptoms, or delayed gut symptoms
Can it cause anaphylaxis?	No	Yes, in IgE-mediated allergy
Are lactose-free dairy products suitable?	Usually	No, because they still contain milk proteins
Dietary approach	Reduce lactose to the amount tolerated	Avoid milk proteins according to an individual allergy management plan

These differences are important when choosing milk, formula and other dairy products.

How are these conditions diagnosed

For lactose intolerance, your doctor may recommend a short trial of reducing lactose, followed by reintroduction while monitoring symptoms.

For suspected immediate milk allergy, skin prick testing or blood tests for milk-specific IgE may support the diagnosis when considered alongside the reaction history.

Skin prick tests and IgE blood tests do not diagnose non-IgE-mediated milk allergy. Diagnosis usually involves a planned period of milk protein exclusion, followed by reintroduction to check whether symptoms return. Your treating team should advise when and where this is safe. Children with immediate reactions or suspected FPIES should not have a home reintroduction without specialist guidance.

Does my child need to avoid all dairy

For lactose intolerance

Usually, no. Many children tolerate some lactose, particularly in smaller amounts. Hard cheeses are naturally low in lactose, and some children tolerate yoghurt. Lactose-free dairy products can also help maintain calcium and protein intake.

The aim is to manage symptoms while keeping the diet as varied as possible.

For cow’s milk allergy

Children need an individual plan for avoiding milk proteins and choosing suitable alternatives.

Standard lactose-free formula, A2 milk and goat’s milk are not suitable substitutes. Babies who need formula may require a specialised formula selected with their doctor and dietitian. Ordinary plant-based drinks must not replace breastmilk or infant formula before 12 months.

Some children tolerate milk baked into foods, but this should only be explored with guidance from their treating team. Many children outgrow milk allergy, although the timing varies and some remain allergic into later childhood or adulthood.

What if I am breastfeeding

Breastfeeding can usually continue.

Removing dairy from your own diet does not reduce the lactose in breastmilk. If your breastfed baby has suspected cow’s milk allergy, your treating team may recommend a time-limited maternal milk protein exclusion and planned reintroduction. This is not needed for every baby.

If an exclusion diet is recommended, a dietitian can help you meet your own nutritional needs while breastfeeding.

How can a paediatric dietitian help

At ChildD, we work with families and their medical team to make dietary changes practical and nutritionally balanced. We can help you:

• Understand which foods need to be avoided and which can stay.
• Choose suitable milk alternatives or infant formula.
• Read food labels confidently.
• Support your child’s growth and nutrient intake.
• Plan reintroduction when your treating team advises it is appropriate.

If you are concerned about symptoms after milk, start with your GP. Seek prompt medical advice for blood in stools, persistent vomiting, poor feeding or concerns about growth.

If your child develops breathing difficulty, tongue or throat swelling, or becomes pale, floppy or collapses during a suspected allergic reaction, give prescribed adrenaline immediately and call 000. Follow their ASCIA Action Plan if available.

About the author

Kathy Beck is an Accredited Practising Dietitian and paediatric allergy dietitian at ChildD in South East Queensland. She has more than 30 years of dietetic experience, including extensive paediatric practice in Australia and England. Kathy contributes to ASCIA’s dietitian education and training activities and helps families manage food allergies with practical, individualised nutrition advice.