CMPA Symptoms: How to spot the signs of milk allergy

By Hannah Whittaker RD, PGDip | Aug 16, 2023

CMPA or cow’s milk protein allergy is one of the most common food allergies in children, estimated to affect around  2-3% of babies before 6 months old. But, CMPA Symptoms can be tricky to diagnose so here I’ll help you with my guide on CMPA Symptoms: How to spot the signs of milk allergy.

Milk allergy occurs when the immune system reacts to proteins in cow’s milk. However, to add to the confusion for parents (me included when my daughters were younger) there are two different types of cows milk protein allergynon IgE and IgE, both which produce some of the same and different symptoms which also vary in severity. Little extra info IgE allergy isn’t always worse than non IgE

It can also be very confusing to know whether the symptoms that your baby shows are due to a cow’s milk allergy or just typical of a baby in their first few months of life. 

In this blog, I will discuss the symptoms of CMPA and how we go about diagnosis, and when to speak to a healthcare professional.

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Milk Allergy Symptoms Blog

IgE vs non IgE mediated allergy.

There are two different types of CMPA

There is IgE (immunoglobulin E) mediated, and non IgE (non immunoglobulin) mediated.  

Immunoglobulins are another word for antibodies. 

Mediated means to cause. 

So an IgE reaction involves antibody production, and in non-IgE reactions, there is no antibody involvement. However, both IgE and non-IgE are food allergies, not intolerances (I hear other health professionals saying this so often and it really gets my back up!)

Non-IgE milk allergy symptoms are often mistakenly diagnosed as lactose intolerance.

What are the symptoms of CMPA?

There are many different symptoms of milk allergy including;

  • Gastrointestinal symptoms (tummy) – stool changes –  mucous and/or blood in stool/constipation/loose stools/abdominal pain/usual baby poop colour – green/yellow/orange
  • Respiratory symptoms – snuffly baby/runny nose/changes in breathing/congestion/in more severe cases analylaxis
  • Skin reaction – rash/reddening/itchy/atopic dermatitis

However symptoms can vary from baby to baby and from mild to moderate to severe symptoms. 

It is important that if you suspect that your baby has a milk allergy you provide a full history to a qualified Milk Allergy Dietitian (like myself). 

When you speak with a health professional they should discuss your baby’s symptoms in detail including the speed at which they happen (are they immediate symptoms or delayed) and also how long they last. This can support the diagnosis of IgE or non-IgE milk allergy. My MILK ALLERGY symptom checker will also help you to log your symptoms before your appointment.

    Symptoms in more detail

    The table below shows you what are the symptoms of CMPA in more detail.

    The key difference I highlight to parents is that IgE reactions are immediate, while non-IgE reactions have delayed symptoms. You will also find that in IgE CMPA that swelling is a symptom, whereas in non-IgE milk allergy swelling does not typically occur. 

    IgE vs Non IgE Milk Allergy Symptoms

    IgE Milk Allergy SymptomsNon IgE Milk Allergy Symptoms
    An immediate reaction within minutes and up to 2 hours after having milk protein. A delayed reaction which happens between 2-72 hours after having milk protein.
    Swelling to lips, face or eyes/
    Skin reaction – hives, raised, itchy rash (urticaria), reddening. Skin reaction – Itchy skin, reddening ‘erythema’, atopic eczema.  
    Gastrointestinal upset – nausea, vomiting, diarrhoea, tummy pain or discomfort,  Gastrointestinal upset – Reflux, vomiting, diarrhoea, blood and/or mucous in stools, constipation, tummy pain or discomfort, irritability. 
    Respiratory – cough, chest tightness, wheezing and shortness of breath. Nasal itching, sneezing, congestion, conjunctivitis. Respiratory – Cough, chest tightness, wheezing and shortness of breath. 
    CMPA Symptoms

    CMPA Rash

    Both IgE and non-IgE milk allergies can cause skin reactions, so it’s crucial to note how soon the symptoms occur.

    CMPA Poo

    In both IgE and non IgE CMPA baby’s there may be changes in stools (poop). Symptoms can range from constipation to very loose stools (some babies can poo up to 20 times per day). Stools may also have mucous or blood present and may change colour.

    Remember, constipation does not typically happen in a baby with an IgE allergy.

    CMPA Poo

    CMPA Respiratory

    Coughing is a symptom of both IgE and non-IgE milk allergy. But if your baby is congested, is always sneezing, or has repeated conjunctivitis then it may be that they have an IgE milk allergy. 

    In a more severe allergic reaction of IgE milk allergy, breathing difficulties can occur; also known commonly as anaphylaxis. Anaphylaxis is a narrowing of the airways and can be life-threatening. If you find your baby showing swelling and breathing difficulty then this requires immediate medical attention. 

    At what age does milk allergy start?

    CMPA symptoms usually can start within the first few weeks after birth, but can be a little delayed and could start anytime up to 2-3 months old. While breastfeeding may not cause any symptoms in some babies, introducing milk products through solid foods (around 6 months) or switching them to formula may trigger symptoms.

    What triggers CMPA?

    CMPA is a condition that is caused by the body reacting to the proteins found in cows’ milk. Depending on the method of feeding (formula fed or breast fed) can depend on the mechanism of a reaction. 

    Formula-fed babies – when a baby with milk allergy has formula milk with cows milk protein contained their body goes into a defense mode recognising the milk protein as an invader. This causes symptoms to occur.

    Breastfed babies – with breastfed babies it can be a little trickier to diagnose as we don’t completely know how much milk protein from the dairy products mum eats gets through her breast milk to the baby.

    This can vary between mum to mum, and baby to baby, however breast milk is thought to contain it is thought to be around 100,000 less milk protein than if a baby was to drink the milk themselves. 

    This reaction will also cause a trigger of your baby’s immune system as it again recognises the milk protein as an invader.  

    However, as mentioned, there are two types of milk allergy. The diagnosis of your baby’s milk allergy will depend on their symptoms’ speed, severity, and duration.

    How to diagnose milk allergy

    Testing for Non IgE CMPA Symptoms

    There is no clinical test for non IgE food allergy. Diagnosis is made via the elimination of the allergen (milk) and then the reintroduction. This helps us check if symptoms disappear when the food is removed and return when the food is reintroduced.

    You don’t always need medical supervision for this; it can be done at home. Depending on whether your baby is breast or formula-fed will depend on how you complete the elimination and reintroduction. 

    Formula fed baby

    In babies that are formula fed, they will likely be trialled on an extensively hydrolysed infant formula. This will need to be given for at least 2 weeks to see if it relieves symptoms. If it does not relieve symptoms and they are more severe an amino acid formula may be trialled. See my blog on Dairy Free formula for more info. 

    After 2-4 weeks a milk challenge should be completed. This is the gold standard for diagnosis and is when cows milk contained formula is reintroduced into your baby’s diet 1oz at a time. 

    Breastfed baby

    When it comes to breastfeeding this works a little differently and the milk will be removed and reintroduced via the maternal diet – you can read more about CMPA Milk Challenge here

    It is important to speak with your Milk Allergy Dietitian or Allergy team if your baby has severe reactions as you may be advised that you cannot complete the milk challenge at home and it should be completed in a hospital setting. 

    Diagnosing milk allergy in formula fed baby
    Imaging showing baby drinking formula milk

    Diagnosing IgE allergy

    Based on the allergy focussed history taken by your doctor or Milk Allergy Dietitian it will have been suspected that your baby has a IgE Milk Allergy. This means that your baby’s body is suspected to be producing IgE antibodies to milk protein.  

    There are two types of tests that are generally completed to diagnose IgE Milk Allergy. 

    These are; 

    1. Skin Prick Testing

    2. IgE blood test

    Skin Prick Testing

    Skin prick testing will take place in the hospital. 

    This is where a small amount of the allergen is placed on the skin to see if a reaction occurs. A lancet pricks the skin painlessly, a solution is placed on the forearm, and the reaction is monitored.

    Again these results should be interpreted alongside a full allergy focussed history. 

    IgE Blood Test

    IgE blood tests (also known as RAST tests in the past), measure the levels of IgE antibodies to milk in the blood. This should be used alongside a full allergy-focused history.

    There is more information on the different types of testing for milk allergy.

    Milk Allergy vs Lactose Intolerance 

    Let’s clear this up, these are two completely different things! Lactose intolerance is the body’s reaction to the natural sugar lactose in the milk. It generally causes tummy trouble and does not involve the body’s immune system (no skin problems or changes in the respiratory tract). Lactose intolerance is also very rare in babies.

    CMPA is an allergic reaction to the protein in cows’ milk. 

    These are two completely different diagnoses. 

    The confusion with diagnosis of milk allergy

    Many symptoms indicate CMPA with varied diagnoses; however, seeking medical advice and taking an allergy-focused history is crucial. That’s where an expert milk allergy dietitian like me comes in. 

    To diagnose your baby with a milk allergy they should show one or more of the symptoms in the table above.

    You may have noticed that a lot of these symptoms are common in young children. This can make diagnosis of a true milk allergy a little tricky. Especially for non IgE dairy allergy. 

    Examples of when it may not be CMPA

    • Reflux – If your baby has reflux, and advised techniques or prescribed medication have relieved it, then it’s unlikely to be due to milk allergy.
    • Constipation – If your baby is constipated and tummy massage, warm baths, or medication have relieved it, then it’s unlikely to be due to milk allergy

    If you have tried all the remedies and symptoms are still continuing then YES it may be that your baby has CMPA. 

    Remember to check out my MILK ALLERGY SYMPTOMS CHECKER and download for FREE Here

    I hope this helps to support you to spot the signs and symptoms of cow milk protein allergy. If you are concerned that your baby has a milk allergy then get in touch. I can help you out with the correct diagnosis.

    Remember that a non-IgE allergy cannot be diagnosed with a blood or skin prick test. This is only for an IgE allergy.

    A non-IgE allergy will need to be diagnosed via elimination diet and reintroduction of milk protein, either via infant formula or when mum is breastfeeding. 

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    CMPA Symptoms


    Hannah Whittaker Dietitian Bump2baby Nutrition
    Expert Pregnancy & Paediatric Dietitian at  | | Website

    Hannah is an Expert Registered Dietitian specialising in Vegan Family Nutrition and Cows Milk Protein Allergy. 

    She is a respected figure in the field of nutrition and a captivating speaker and sought after media spokesperson being featured in esteemed publications including the Sunday Times, Independent and Huffington Post.


    Registered Dietitian
    First Class Degree in Nutrition


    Over 15 years experience working in the field of nutrition
    Respected Media Spokesperson both in the UK & USA; quoted online, TV and in local and international news
    Writer & Researcher, supporting the BDA and PEN Nutrition



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