How do I know if it's cow's milk allergy or lactose intolerance?

green ribbon cmaCow’s milk allergy and lactose intolerance are often confused with each other, but they are not the same. Find out in this section what the difference is – this will help you to discuss your baby’s health with your doctor who can then decide how best to provide a solution to the problem.



CMA Questionnaire

What is CMA triggered by?

Cow’s milk is made up of lots of different components, for example proteins (such as casein and whey), milk sugar (called lactose) and fat.

Milk Lactose Diagram

The allergic reaction happens because the immune system mistakes the proteins in cow’s milk to be a threat, when in fact they should be harmless. It then releases chemicals such as histamines and others – it’s these chemicals that trigger the signs and symptoms of an allergic reaction.

Lactose intolerance is triggered by the lactose sugar in cow’s milk. In people with lactose intolerance, the digestive system can’t fully digest this milk sugar, because it doesn’t make enough of the lactase enzyme. So instead of being digested and absorbed, the lactose stays in the gut and feeds the gut bacteria, which release acids and gases that cause the symptoms of lactose intolerance.

Who gets it?

Cow’s milk allergy tends to affect younger children under the age of 3 years. Most will grow out of this food allergy as they get older, often by the time they start school.

Good to know

In some cases, people can develop lactose intolerance when their gut becomes damaged through illness, surgery or certain medications (this is called secondary lactase deficiency). In these cases, the lactose intolerance can be temporary or permanent. It can sometimes develop after an episode of gastroenteritis.

Only in very rare cases does lactose intolerance affect babies from birth (called congenital lactase deficiency). In this case, the person remains lactose intolerant for life.

What are the symptoms?

Cow’s milk allergy and lactose intolerance can share some of the same signs and symptoms, including feeding and bowel problems such as:

  • Wind
  • Diarrhoea
  • Bloated tummy
  • Tummy aches and cramps
  • Tummy rumbling
  • Feeling sick

However, since cow’s milk allergy involves the immune system, babies who are allergic to cow’s milk protein will also show allergy symptoms like an itchy rash, wheezing, or runny noses and coughs. These aren’t seen in lactose intolerance, as this condition doesn’t involve the immune system.

Another difference is that with cow’s milk allergy, even a small amount of cow’s milk protein could give your baby an allergic reaction. In contrast, many people with lactose intolerance can often eat small amounts of milk products without noticing any symptoms.

Symptoms diary

How is it diagnosed?

There are different tests for cow’s milk allergy and lactose intolerance, so it’s important that you discuss your child’s symptoms in detail with your doctor, who will decide which tests are most appropriate to get the right diagnosis.

If cow’s milk allergy is suspected, your doctor may request an allergy test such as a skin prick test or blood test, and/or advise you to put your baby on an elimination diet followed by a food challenge.

If your doctor thinks it may be lactose intolerance, he or she may request a hydrogen breath test, lactose tolerance test, milk tolerance test or stool sample. You can find out more about these different tests from NHS Choices.

How is the condition managed?

Since cow’s milk allergy and lactose intolerance are caused by two different problems, there are slightly different ways of managing the conditions.

Cow’s milk allergy is managed by completely eliminating cow’s milk protein from your baby’s diet, as even a small amount of cow’s milk protein could potentially trigger an allergic reaction.

Initially, lactose intolerance may be managed by completely eliminating cow’s milk protein from the diet too. However, an entirely dairy-free diet is rarely needed in the long term. Most people with lactose intolerance are able to digest some lactose, as they still have a low level of the enzyme, lactase. This means that some dairy products can be carefully reintroduced into the diet – how much depends on the individual, so it’s important to follow the guidance of a dietitian when doing this. Some babies will benefit from having a lactose-free infant formula.

In either case, it’s important that you don’t make any changes to your child’s diet without the supervision of a healthcare professional. Be sure to speak to your doctor if you’re concerned that your infant might have cow’s milk allergy or lactose intolerance.

If your baby is diagnosed with cow’s milk allergy, find out more about how to look after your baby in the long term.