Baby milk allergy and intolerance symptoms

Babies can either be allergic or intolerant to milk. Because some of the symptoms of milk allergy and milk intolerance are similar, they can be difficult to diagnose.

A milk allergy involves an immune reaction to one or more of the proteins present in milk, whereas an intolerance does not involve the immune system. An intolerance is caused by an inability to deal with certain substances in milk, such as lactose. One example which is often talked about is lactose intolerance, where some individuals don't produce any or enough of the enzyme lactase which breaks down lactose. Undigested lactose causes uncomfortable symptoms like diarrhoea, bloating and wind.

Watch our video to understand the difference between allergy and intolerance, and how to recognise the associated symptoms.

If your baby is allergic to milk, they will react to infant formula which is based on cows’ milk and sometimes, but very rarely, your breast milk if you’ve recently consumed dairy products. Symptoms to look out for include stomach cramps, vomiting, diarrhoea, rashes, hives, eczema, and difficulty breathing. Individual symptoms can sometimes be related to a bug, but if your baby is affected in two separate areas of the body – for example, the stomach (vomiting) and skin (hives) – you should ask your health visitor or doctor for advice.  

It’s common for babies who are allergic to cows’ milk to be allergic to goats’ milk and sheep’s milk too, as they contain similar proteins. Unfortunately, there is no single diagnostic test for cows’ milk allergy and a combination of tests and a series of elimination and reintroduction diets are often necessary. These tests usually happen once your baby has been referred to a specialist by your doctor. It's very important that you seek advice from your doctor if you suspect that your baby has an allergy so that they can be properly diagnosed and treated.

Giving your doctor as much detail about your baby’s symptoms as possible can help speed up the diagnosis process. By keeping a diary of their symptoms, including when they occur and how long they last for, you can help your doctor identify or rule out CMA. Taking photos of any skin reactions, such as a rash, can be helpful too. You should also let your doctor know if there is a history of allergy in your family. For more detailed information, read our article on how to get a diagnosis for CMA.

Managing a cows’ milk allergy involves removing all cows’ milk from your baby’s diet, so you'll need to get familiar with reading food labels and ingredients, as milk can occur in unlikely places. Food labelling laws are there to help you, and common allergens, like milk, have to be declared on pre-packaged foods.

If your baby is being formula fed and has been diagnosed with cows’ milk allergy, your doctor may prescribe an extensively hydrolysed formula. The protein in these formulae has been broken down into smaller pieces so that the baby’s immune system does not recognise it as an allergen – a process which does not affect the nutritional value of the formula.

Soya formulae are not recommended before 6 months as they contain phytoestrogens (plant-based compounds with oestrogen-like properties), and infants who react to cows’ milk-based formulae often also react to soya-based formulae.

In rare cases your baby may be reacting to the milk proteins passing from your diet into your breast milk. If your baby is diagnosed with cows’ milk allergy and you’re breastfeeding, you may have to change your diet – but this should only ever be done after consulting your healthcare professional, as it is quite rare.

Managing a cows’ milk allergy involves removing all cows’ milk from your baby’s diet.

When introducing solid foods to a baby with a milk protein allergy, you'll need to get familiar with reading food labels and ingredients, as milk can be found in unlikely places. Whilst this might seem overwhelming at first, keep in mind that food labelling laws are there to help you, and common allergens, like milk, must be declared on pre-packaged foods.

Only around 2–7.5% of babies under 1 year old are allergic to cows’ milk¹. By the age of three most children will have grown out of cows’ milk allergies, but for a few it may last until they're 6–8 years old. Occasionally, it can continue into adulthood – especially if there is a family history of allergies².

A baby with a lactose intolerance usually experiences less severe reactions than one with an allergy. As with a milk allergy, symptoms of lactose intolerance can include diarrhoea, vomiting, and stomach cramps but not usually hives or breathing difficulties. Another difference is that a lactose intolerance won’t show up in a blood or skin-prick test. Still, your baby’s reaction will be noticeable, if not as severe as that of an allergy. 

There are two main types of lactose intolerance. The first is primary lactose intolerance, and is caused by a deficiency in the enzyme lactase. It normally affects Hispanic, Asian and American Indian populations, but is uncommon in Europeans – also, the condition doesn’t often cause symptoms in the first year of life. But it doesn’t mean that lactose has to be removed from the diet entirely: depending on the individual, those with primary lactose intolerance can often tolerate a certain amount of lactose.

Secondary lactose intolerance is usually caused by damage to the gut, after a severe stomach bug, for example. But this form of the condition is usually temporary, until the gut heals. In very severe cases, lactose may need to be removed from the diet for a few weeks, but should only be done so on the advice of a healthcare professional.

Before you worry too much about milk allergies and intolerances, it’s worth remembering that babies and small children often pick up common bugs when they come into contact with other children, which can have similar unpleasant effects. But if your baby’s symptoms persist or you notice a pattern occurring, you should seek advice from your doctor.