Cow's milk allergy in babies: IgE and non-IgE

What cow’s milk allergy is

Cow’s milk allergy happens when a baby’s immune system reacts to the proteins in cow’s milk (casein and whey). It’s one of the most common food allergies in young children: ACAAI estimates that 2% to 3% of children under 3 have it. It often first shows up when a baby starts cow’s milk formula, or when dairy is added during weaning.

It’s not the same as lactose intolerance. Lactose intolerance is trouble digesting the sugar in milk, it doesn’t involve the immune system, and it’s rare in babies.

Doctors talk about two main types. They behave differently, are diagnosed differently, and can be managed differently, so it’s worth knowing which one your baby’s doctor suspects.

The fast type: IgE-mediated

This type involves an antibody called IgE. Symptoms usually start within minutes and up to 2 hours after milk, and can affect several parts of the body:

• hives or a red, itchy rash
• mild puffiness of the face or around the eyes (lips or mouth that suddenly swell are a sign of anaphylaxis, below)
• vomiting
• coughing, wheezing or a runny nose

Rarely, it can cause anaphylaxis, a severe reaction that needs emergency treatment.

Signs of anaphylaxis are trouble breathing, wheezing or a cough that won’t stop, swelling of the tongue or throat, lips or mouth that suddenly swell, a hoarse cry, turning pale or floppy, becoming very sleepy or unresponsive, or signs in more than one part of the body at once. If you see any of these and your baby has an epinephrine (adrenaline) auto-injector, use it right away, then call for an ambulance. Call 911.Call 999.Call your local emergency number (such as 112 in Europe or 000 in Australia). If you don’t have an auto-injector, call straight away. Keep your baby lying down, never standing or walking (on their side if they’re vomiting, head and shoulders a little raised if breathing is hard). See signs of anaphylaxis.

The delayed type: non-IgE-mediated

This type doesn’t involve IgE. Symptoms are delayed, usually by hours, and the NHS says they can take up to 3 days to appear. They mostly affect the gut, and can be easy to confuse with common baby problems like colic or reflux:

• vomiting or reflux
• diarrhea, or constipation
• blood in the poop
• tummy pain, crying and fussiness
• eczema getting worse
• poor weight gain

Most babies with this type have mild to moderate symptoms. At the severe end is FPIES, which causes repeated vomiting a few hours after milk and can make a baby pale and floppy. If your baby vomits once or twice a few hours after milk and is alert and like themselves, call your pediatrician or GP. Call 911 or go to the emergency room if your baby is vomiting again and again, or is pale, floppy, very sleepy or hard to wake.Call 999 or go to A&E if your baby is vomiting again and again, or is pale, floppy, very sleepy or hard to wake.Call your local emergency number (such as 112 in Europe or 000 in Australia) or go to the emergency department if your baby is vomiting again and again, or is pale, floppy, very sleepy or hard to wake. See FPIES.

How it’s diagnosed

Don’t diagnose it yourself, and don’t switch formulas or cut out dairy without talking to your pediatrician or GP first. Many of these symptoms have other causes, and cutting out a major food without advice can leave your baby short of nutrients.

• For the fast type, your doctor or an allergist will ask what happened and may arrange a skin prick test or a blood test for IgE.
• For the delayed type, there’s no reliable skin or blood test. Doctors usually suggest removing cow’s milk for 2 to 4 weeks, then adding it back as they advise. If the symptoms clearly improve without milk and come back when it’s added back, that supports the diagnosis. Your doctor decides when and how to try milk again.

Feeding a baby with cow’s milk allergy

If you’re breastfeeding, keep going. Milk protein passes into breast milk only in small amounts. If your doctor thinks your baby is reacting to it, they may suggest you cut dairy from your own diet. Only do this with medical advice, and get support with calcium and vitamin D.

If your baby has formula, they’ll need a special one:

• An extensively hydrolyzed formula, where the milk proteins are broken down, is usually the first choice. It works for most babies.
• An amino acid formula may be needed if symptoms continue or the reaction is severe.

These formulas don’t work for cow’s milk allergy, so don’t switch to them:

• goat’s or sheep’s milk formula: the proteins are too similar to cow’s milk
• “comfort” or partially hydrolyzed formula: the proteins aren’t broken down enough
• lactose-free formula: it still contains cow’s milk protein

Starting solids with cow’s milk allergy

Babies with cow’s milk allergy can start solids at around 6 months, like other babies. Just leave out dairy:

• no yogurt, cheese, butter or cow’s milk in cooking
• no goat’s or sheep’s milk, cheese or yogurt either, unless your doctor says otherwise: ACAAI notes that people allergic to cow’s milk may also be allergic to milk from other animals
• read labels: milk protein can be listed as milk, casein or whey, and turns up in foods you might not expect, such as some sausages and canned tuna
• give iron-rich foods and a wide variety of other foods

Cow’s milk allergy doesn’t mean holding back other allergens. Introduce egg, peanut and the rest one at a time, as for any baby, unless your doctor advises otherwise: see how to introduce allergens. If your baby also has severe eczema, see eczema and starting solids.

At 12 months, your baby still can’t switch to cow’s milk as a drink. Ask your doctor or a dietitian about the best alternative. Don’t use rice drinks: the NHS says children under 5 shouldn’t have them because of arsenic.

Will my baby outgrow it?

Most children do. A 2023 Canadian review estimates that more than 75% of children with cow’s milk allergy outgrow it by age 3, and more than 90% by age 6. For some it takes longer: ACAAI cites a study in which fewer than 20% had outgrown it by age 4, though about 80% had before age 16.

Some children with milk allergy can eat milk that has been well baked into food, such as a muffin, before they can have it any other way. Milk is usually brought back gradually, but only when your doctor or dietitian says it’s time, and following their plan. For the fast (IgE) type and for FPIES, milk is usually reintroduced under medical supervision, not at home.

Where US and UK advice differs

• Soy formula. The AAP doesn’t recommend soy formula for babies with cow’s milk allergy, because up to half of them also react to soy. The NHS says soy formula can occasionally be used, but only from 6 months and only under medical supervision.
• Getting the formula. In the UK, a GP prescribes the hypoallergenic formula. In the US, ask your pediatrician which formula to buy, since these are more expensive than regular formula.
• The “milk ladder”. The “milk ladder” comes from UK primary care guidance for mild to moderate delayed-type allergy: a step-by-step plan for adding milk back at home, ideally led by a dietitian. That guidance says it shouldn’t be used for the fast (IgE) type or for FPIES.