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What is a cow’s milk allergy?

Cow’s milk allergy (also known as cow’s milk protein allergy or CMPA) is an abnormal response by the body’s immune (defence) system in which proteins in a food (in this case cow’s milk) are recognised as a potential threat. This can cause the immune system to be ‘sensitised’. When this happens, there is the potential that when cow’s milk is consumed the immune system remembers this protein and may react to it by producing allergic symptoms.

Whilst cow’s milk allergy is one of the most common food allergies to affect babies and young children in the United Kingdom it is still rare. Formula fed babies, although very rarely, breastfed babies can also be affected. Allergic symptoms to CMPA can happen immediately after feeding or they can be delayed. In the case of immediate symptoms such as swelling of the lips or the tongue or breathing difficulties, immediate medical help must be sought.

Types of cow’s milk allergy

There are two types of cow’s milk allergy depending on how the immune system reacts. Symptoms that are ‘immediate’ (quick to appear) are caused by the immunoglobulin E antibody (called IgE). Typically these allergic symptoms happen within minutes of consuming cow’s milk or up to two hours afterwards. This type of reaction is described as IgE mediated food allergy.

The other type of milk allergy happens when symptoms are ‘delayed’ (slow to appear) and are caused by a different part of the immune system reacting in a different way. This type of reaction is described as Non-IgE mediated food allergy and is the most common type. The symptoms typically develop from two hours after consumption but can take up to 72 hours. If cow’s milk continues to be consumed in the diet, the immune system will continue to produce such symptoms over days or even weeks.

Symptoms of cow’s milk allergy

Symptoms of CMPA often start in the early weeks and months of life. There are many possible symptoms which may suggest your baby has a cow’s milk allergy. Allergic symptoms can affect one or more of the body’s systems, including the skin, digestive and, less commonly, breathing or blood circulation. Allergic symptoms may be called mild, moderate or severe. However, it is important to note that some of these symptoms, such as reflux, colic and constipation are commonly seen in this young age group.

The immediate symptoms (see table below) occur quickly after consuming cow’s milk. They are most likely to be seen when weaning starts from breast feeding or when a change is made from breast feeding to formula feeding. The symptoms will usually be mild-to-moderate and often only affect your baby’s skin. It is very rare to see severe symptoms which can affect your baby’s breathing or how alert they appear. However, if you recognise such worrying severe symptoms, you should call an ambulance immediately as they could be potentially life threatening. This form of allergic reaction is called Anaphylaxis. Tell the emergency call handler that you suspect that it is an anaphylactic (pronounced ana-fi-lac-tic) reaction.

The delayed symptoms appear much more slowly and are also more likely to be mild-to-moderate. They are more difficult to relate to being caused by cow’s milk as they happen several hours after cow’s milk is consumed.

Key Message: Remember that many of the symptoms of delayed allergies, such as eczema, colic, reflux and diarrhoea are common in infants and milk allergy is only one of a number of possible causes. In most cases of cow’s milk allergy, your baby will show several symptoms in a pattern that will suggest either the delayed or immediate type of food allergy. Some of the symptoms can appear in both immediate and delayed allergic reactions. However, how quickly symptoms are seen usually gives the indication for the type of reaction.

Are there other types of reactions to cow’s milk?

Cow’s milk is made up of three main ingredients – protein, sugar, and fat. In cow’s milk allergy, it is the proteins called casein and whey that usually cause the problem. However, the sugar (lactose) in milk can also cause symptoms in some. This is referred to as Lactose Intolerance. It is important to understand the difference between lactose intolerance and cow’s milk allergy and to be aware that the management of lactose intolerance is very different from that of cow’s milk allergy. There are two types of lactose intolerance.

Primary Lactose Intolerance is the more common form and happens where there are reduced levels of the enzyme lactase in the digestive system. This enzyme is needed to break down lactose sugar found in milk, which the body can then absorb and use. As young children grow up and drink less milk, the amount of this enzyme gradually and naturally decreases. For some children, especially those from Asian or African ethnic backgrounds, this may mean that over time not all the lactose in the diet is broken down. Very gradually tummy symptoms begin to develop when lactose in milk is consumed. These symptoms may include bloating, tummy pains, wind and very loose poos (diarrhoea) – all of which can also be seen in milk allergy. However, this does not usually happen until later in childhood and is very unlikely to occur in young babies, which is the group most likely to show symptoms of cow’s milk allergy.

Secondary Lactose Intolerance occurs in some babies and older children who have been unwell with a gastroenteritis infection or who have been diagnosed with other digestive system related conditions such as coeliac disease. These conditions may cause temporary damage to the digestive system and reduce lactase enzyme levels, resulting in lactose intolerance symptoms. This is usually temporary and can be expected to resolve after a short period of time once the main cause has settled.

Key Message: The symptoms of both types of lactose intolerance can also be seen in milk allergy. This can lead to confusion with the mistaken conclusion that symptoms are due to lactose intolerance when the real reason is cow’s milk allergy.

Play video

Kate and Eben's Story

Kate found out that her firstborn, Eben, had a cow's milk allergy, after he suffered from a reaction following a few spoonful's of yoghurt. The experience was terrifying for new mum Kate.

What should I do if I suspect that my child has symptoms of Cow’s Milk Allergy?

The key message: Do not delay in seeking advice from your GP or Health Visitor. They will be able to assess whether the symptoms may be due to milk allergy or there is another cause.

They will listen to your concerns and take an allergy focused history (a series of questions to help decide if allergy is a possible cause of the symptoms). It may be necessary for the doctor to carry out a physical examination. To get the best from your appointment, it may be useful to write down the answers to the questions below before attending and take them with you for discussion.

  • What signs and symptoms have you noticed and are concerned about?
  • When did the symptoms first start?
  • How long do they last?
  • Have you started weaning yet? Any other food eaten, amount and form (for example as a drink, added as an ingredient in a food, cooked, baked).
  • How has your baby been fed: breast milk, formula, or mixed fed (breast and formula feeds)?
  • Do you know or suspect a food is triggering the symptoms?
  • How quickly or slowly did the symptoms appear?
  • Do such symptoms appear each time the suspected food is given?
  • How much of the suspected food does your child need to eat for symptoms to appear?
  • Are there any existing allergic conditions (asthma, eczema, hay fever, food allergy) or family history of such allergy? (This can increase the likelihood of your baby having a food allergy).
  • Have you tried any medication or dietary changes?

There are still unacceptable delays in children receiving a diagnosis, with 43 per cent of cases waiting more than three months and 15 per cent visiting their GP ten times before a diagnosis. – Parent Survey Results.

What tests are needed to diagnose each type of Cow’s Milk Allergy?

Testing will only be discussed after a detailed allergy focused history has been taken. It will depend on the suspected type of cow’s milk allergy.

Suspected Immediate (IgE mediated) allergic reaction

If immediate (IgE mediated) cow’s milk allergy is suspected your GP is likely to arrange a referral to a children’s specialist allergy service for allergy testing and further management. The two tests which help diagnose IgE reactions are a skin prick test and a specific IgE antibody blood test (previously referred to as a RAST test). Usually the information from the allergy-focused history and the tests will be enough to confirm the diagnosis. However, if information and/ or results of the tests are not clear, then an oral milk challenge (a supervised and gradual feed under the guidance of a doctor or nurse in a hospital or allergy clinic setting) may be needed to confirm or exclude whether there is an IgE mediated cow’s milk allergy.

The referral process and waiting times to see a specialist will depend on where you live, and the allergy service and resources in your area. Allergy UK’s Helpline on 01322 619 898 can help signpost you to an approved NHS or Private allergy clinic. If you choose not to be seen through the NHS you have the choice to pay to see a private allergy doctor. Whilst waiting for an NHS or private appointment, your GP or Healthcare Professional should advise you on the dietary changes that you will need to start immediately.

Suspected Delayed (Non-IgE mediated) allergic reaction

If delayed (Non-IgE mediated) cow’s milk allergy is suspected, skin prick testing and/or blood tests are not helpful. The diagnosis for delayed allergy needs to be confirmed or excluded by starting a trial elimination of all cow’s milk protein; either from you baby’s diet in the case of a formula fed baby or from your own diet if you are exclusively breast feeding. Those babies who are formula fed need to be prescribed a special low allergy formula (called a hypoallergenic formula).

If it appears that your baby has reacted to cow’s milk protein coming through in your breast milk, you will need to eliminate all cow’s milk and all products containing cow’s milk from your own diet. This trial elimination diet will need to be guided by your GP or healthcare professional. If you are still exclusively breast feeding, your doctor may well wish to refer you to a dietitian to ensure that both your on-going nutritional needs and those of your baby are being met.

In the more common case of the suspected allergy symptoms being considered mild-to moderate, the length of the trial will usually be for two to four weeks (minimum 2 weeks). At the end of this agreed trial, your GP will advise you on how to gradually reintroduce cow’s milk back into your child’s diet at home. This process will show whether any clear improvement seen in the symptoms during the trial elimination was actually due to milk allergy. If allergy is the cause, the symptoms can be expected to return within the first few days of reintroducing cow’s milk. If this happens, it will be necessary to return to the cow’s milk free diet and the symptoms will usually settle again and the diagnosis of cow’s milk allergy is now confirmed. It is very important that the diagnosis is confirmed by this elimination and reintroduction trial as per the NICE Quality Standard for food allergy (QS118). If these guidelines are not followed, delayed onset cow’s milk allergy is likely to be over diagnosed and lead to the inappropriate management of symptoms, as well as an unnecessarily restrictive diet.

In the less common case where the suspected allergy symptoms are considered severe, your doctor will still need to advise starting this elimination diet. However if a clear improvement should be seen in the symptoms your doctor should not be advising any reintroduction of cow’s milk protein at home to confirm the diagnosis. The diet should be continued and the need for early referral to a children’s specialist allergy service for ongoing assessment and care should be discussed and made as soon as possible.

Where there has been no clear improvement in symptoms during any elimination trial, milk allergy is unlikely to be the cause of your baby’s symptoms. Your GP will usually advise returning to a normal diet and should continue to consider other possible causes for the symptoms.

Alternative Tests for Food Allergy

The National Institute for Health and Care Excellence (NICE) recommends that testing should not be sought from unreliable sources such as online or alternative practitioners. Such testing may include kinesiology, hair analysis, Vega testing and other blood tests. These should be avoided as there is no scientific evidence to support their use in diagnosing any food allergy and such testing may result in the unnecessary removal of important food groups from your baby’s or child’s diet.

Choice of alternative cow’s milk substitutes 

A cow’s milk free diet means avoiding the proteins in cow’s milk, which are called whey and casein, and also avoiding milks from many other four legged mammals as their milk proteins are so similar. Therefore, goat and sheep milks are not suitable alternatives for children suffering from cow’s milk allergy.


Breast feeding provides the best source of nutrition for your baby. Breast fed babies can react to milk proteins that are transferred in breast milk from the mother’s diet. If it is suspected that a baby is reacting to cow’s milk protein via breast milk, a mother may be advised to avoid cow’s milk and dairy products in their diet while breastfeeding. This involves a trial of up to six weeks to see if the baby’s symptoms improve. If they do not and the breast-feeding mother had been following a strict cow’s milk free diet, she can then return to her normal diet.  

Hypoallergenic formula:  

In babies who are solely infant formula fed or are given infant formula in addition to breast milk, the formula will need to be changed to a hypoallergenic (low allergy) infant formula. Extensively hydrolysed infant formulas still contain cow’s milk protein, but the proteins have been broken down into smaller pieces so the immune system is less likely to identify them as harmful. Most infants with cow’s milk allergy will be able to tolerate these. For those who still have symptoms on an extensively hydrolysed formula, an amino acid formula is required. This formula is not based on cow’s milk and the protein is completely broken down.’ The GP, health visitor or dietitian may make recommendations about these formulas which are available on prescription from the GP. This will take into account the baby/child’s age, how severe allergic reactions are, other allergic conditions or a family history of allergy and dietary needs. For more information on suitable milk substitutes for your baby, see the BDA factsheet.

Moving onto a hypoallergenic formula:  

It can be difficult to get a baby to accept a different formula and hypoallergenic formulas have a different taste and smell to ordinary infant formula. Most babies under three to four months of age will readily accept the change. For older babies and children who have delayed allergic reactions, it may help to gradually introduce it over a number of days, mixing it with their usual milk until they get used to it or, failing that, adding a drop of vanilla essence/extract (ensuring that this is alcohol free) to the bottle. You may notice during this change that your baby’s poo changes colour (dark green) and they may also poo less often. This is quite normal and is not a cause for concern. 

Once a cow’s milk allergy diagnosis has been made, your baby or child will need regular assessment by a dietitian to make sure that they are still on the most suitable formula or alternative milk substitute. If your baby or child appears to be growing out of their milk allergy, and after starting a supervised gradual re-introduction of cow’s milk, they can tolerate some foods containing cow’s milk, a dietitian can advise on when and how to stop the formula. 

For more information on alternative options to cow’s milk allergy, see our cow’s milk free diet informatinon sheet for babies and children.

Ongoing support for cow’s milk allergy

Your GP is responsible for the diagnosis process and for providing ongoing care, with support from a dietitian for any confirmed mild-to-moderate type of delayed onset Non-IgE mediated cow’s milk allergy. They will usually advise referral of any suspected severe Non-IgE mediated and all suspected immediate onset IgE mediated milk allergy to a children’s specialist allergy service.

Fortunately, most children will grow out of their cow’s milk allergy in early childhood. Until that happens, your GP or allergy specialist will work with you, usually with the supporting help of a dietitian, to ensure that your child remains healthy whilst excluding all forms of cow’s milk from their diet.

Travelling with an allergic infant

Travelling with an infant or child involves a lot of preparation and planning – this can be overwhelming, in addition to thinking about the needs of a food allergic infant or child. There is no one ‘rule that covers all’, and restrictions on quantity and storage of specialist allergy milk products (including milk alternatives, such as soya milk) will vary from one type of transport carrier to another. Individual carriers may have further detailed information on allowances and restrictions, under the ‘family travel’ section of their website.

Breast milk

Breast milk can be carried in hand luggage even if you are not travelling with a baby. Expressed breast milk in containers up to 2,000 ml is allowed, however frozen breast milk is not permitted.

Formula milk

Formula milk, cow’s milk, other types of milk, sterilised water, and baby food are not subject to the100ml hand luggage restrictions that applies to other liquids, gels, and aerosols. However, this is only true if you are travelling with the baby. In addition, baby milk or food does not need to fit into a transparent bag, but will need to be available for inspection by security staff if requested. A concept of a ‘reasonable quantity’ is mentioned on many of the transport carrier’s websites with no formal guidance, and will be at the discretion of the security screening officer at customs.

Allergy UK’s Dietitian Service

We know that being a parent isn’t easy at the best of times, so when you add a poorly baby with suspected allergy into the mix, we understand that family life can become complex and emotionally challenging.

Allergy UK’s Dietitian Service provides specialist allergy advice to help inform and guide parents of children from 0-5 years old who are presenting with symptoms of food allergy.

Find out more here.

Weaning your child

We know that being a parent isn’t easy at the best of times, so when you add a poorly baby with suspected allergy into the mix, we understand that family life can become complex and emotionally challenging. Conflicting advice is also often given through various channels, creating a lot of additional confusion and anxiety.

Allergy UK have developed this Weaning Support Pack together with leading specialists and with the help of parents with food allergic children.

Find out more here.

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