It might seem odd that something in your baby’s milk could end up blocking their nose or making them wheeze. But CMA is not just about the tummy, it’s an immune system reaction that can affect the whole body, including the airways.

Here's what happens in simple terms: your baby’s immune system wrongly identifies the proteins in cow’s milk as a threat. This triggers an allergic reaction, causing the release of chemicals such as histamine, which can lead to symptoms like coughing, wheezing, and rashes.² In the nose and airways, this means swelling, irritation, and too much mucus being produced. The airways can also narrow, which is what causes that wheezy, high-pitched sound especially when your baby is sleeping.

There are two types of CMA reactions, and it's helpful to know the difference:

These happen quickly, usually within minutes to two hours of having milk. Symptoms tend to be more obvious and can include sudden wheezing, hives, or vomiting.³

These reactions build up over hours or even days after a feed.³ Babies with this type are often just described as 'always congested', they snuffle constantly, have a runny or blocked nose all the time, and may breathe noisily, especially at night. Because the reaction is delayed, it can be really hard to connect it back to a feed.

This delay is one of the main reasons CMA respiratory symptoms get missed. By the time your baby starts coughing or wheezing, the bottle or breastfeed/chestfeed that triggered it may have been many hours ago.

CMA can cause a range of respiratory symptoms.⁴  Here’s what they might look like:

Your baby might have seemed congested almost since birth. Saline drops from the pharmacy may help a little, but they don't fix the root cause, which may be ongoing irritation from the milk protein.

Especially one that seems worse after feeds. CMA can be suspected in babies who regularly cough after being given cow's milk/ dairy-based formula.^1,5

This is a high-pitched, whistling sound when your baby breathes out. It's similar to asthma, but in this case, it's caused by an allergic reaction to milk, not by asthma itself. It's often more noticeable at night.

Your baby may seem to always be trying to clear their nose, and their breathing may sound 'noisy' even when they're resting or asleep.

Some babies may present mainly with respiratory symptoms, although CMA usually involves more than one body system.⁴

This is where things can get confusing, because a blocked nose and a cough can have lots of causes. Here are the most common things CMA gets mistaken for:

If your baby has older siblings, or regularly mixes with other babies, coughs and colds are common. Infections usually cause a fever and improve within 1–2 weeks. CMA symptoms are more likely to persist, occur without a temperature, and not improve on their own.

This is a common condition in babies and a common cause of noisy breathing in newborns,^6,7 and can sound similar to CMA-related wheeze. The important difference: with laryngomalacia, the sound is mainly when breathing in,⁶ and it is usually present from the very first days of life.^6,7

A very common condition in infancy (i.e. before 1 year of age), specially in winters. It’s usually caused by a respiratory virus like RSV of Influenza virus and is a self-limiting condition and usually gets better in 5-7 days. 

Asthma is rare in babies but some older infants (usually after 3 months) may get a similar illness called Viral Induced wheeze which is triggered by a virus and causes the constriction of airways leading to breathing difficulty and whistling sound.

If you're not sure which it is that's completely normal. That's exactly what your GP or specialist is there to help with.

Usually, babies with CMA also have other symptoms as well as respiratory symptoms, like persistent eczema, reflux (bringing up milk) or excessive colicky discomfort, loose poos and in later stages can pass blood and/or mucous in the stool. Not all symptoms need to be present for a diagnosis but when present together, it helps in making a diagnosis of CMA.

If you think CMA might be behind your baby's breathing symptoms, book an appointment with your GP. Describe exactly what you see, especially if symptoms seem worse after feeds. They may try an elimination diet, or refer you to a paediatric allergy specialist. It’s important that you do not ‘self-diagnose’ as eliminating milk from your diet may not be a good idea, if it’s not required. Also, there might be some alternative diagnosis which will get missed and there will be a delay in diagnosis if not seen by a specialist in time.

But some symptoms need immediate help. Call 999 or go straight to A&E if your baby:

• Is struggling to breathe or getting worse quickly
• Has their chest sucking inwards with each breath
• Goes blue around the lips or face
• Suddenly develops swelling of the face, lips, or throat, or breaks out in widespread hives
• Becomes floppy, very drowsy, or unresponsive

These can be signs of anaphylaxis; a severe allergic reaction that is a medical emergency.⁸ Don't wait and see. Call 999 straight away.

Once CMA has been confirmed, the next step is usually to remove cow’s milk protein from your baby’s diet under the guidance of a healthcare professional. Many babies experience an improvement in their symptoms within a few weeks.

• If your baby is exclusively breastfed/chestfed and having symptoms: the mother/feeding parent will need to follow a completely dairy-free diet as the proteins from dairy (milk proteins) pass into breastmilk (human milk) and can still cause a reaction.
• If your baby is mixed or formula-fed: Your GP can prescribe a special formula. Most babies are given an Extensively Hydrolysed Formula (EHF), where the milk proteins are broken down so the body no longer reacts to them. For more severe cases, an Amino Acid-based Formula (AAF), which is a formula containing individual amino acids, which is the most basic form of proteins may be prescribed. All of these hypoallergenic formulas are available on prescription only.

If your gut is telling you something isn't right about your baby's breathing, trust it. You know your baby better than anyone. Speak to your GP, describe what you've noticed, and suggest whether CMA could be playing a role.

Nutricia offers a range of additional resources that you may find helpful. These can be accessed via the Nutricia website, where you'll find dedicated sections providing further practical information and support. If you'd like any additional guidance, the Nutricia Resource Centre team is always happy to help on 03457 623653.

Written by Dr Ramnik Mathur

Dr Ramnik Mathur is a Consultant Paediatrician with an MSc in Allergy and a special interest in Cow's Milk Allergy (CMA). He has more than 25 years of experience in paediatrics and over a decade of experience managing allergic conditions. He regularly cares for babies and children with CMA in both NHS and private healthcare settings across London.