December 13

What is the Difference between Milk Allergy and Lactose Intolerance?


Why do lactose intolerance and cow’s milk allergy often get mixed up with each other?

Lactose intolerance and cow’s milk protein allergy are often discussed together, and the two often get confused. This could be because both conditions involve milk and because children may have to avoid normal dairy products as well as the fact that some individuals may share some symptoms such as tummy pain and diarrhoea.  However, the conditions are very different in many ways and the two should be clearly differentiated from each other. This is to ensure that children with these conditions and their parents/caretakers get the correct guidance and advice on what products their child should avoid, how to prevent possible nutrient deficiencies from developing, and how to handle a possible adverse reaction.

In this blog, I’ll discuss them first separately and then together to hopefully give you a better understanding of how these conditions differ from each other and why it is important to understand the difference.

Lactose intolerance

To gain a better understanding of lactose intolerance we need to first understand what lactose actually is. Lactose is a sugar that occurs naturally in dairy products which accounts for most of the calories in milk.  It’s not only found in cows’ milk but also in other mammal’s milk such as the milk of goats and sheep. Foods that contain lactose include milk, yoghurt, cream, cheese, and ice cream. However, it is important to note that lactose may often be used as an additive in processed foods such as ready-made sauces, baked goods, and cereals, and therefore it is important to check food labels.

Now that we understand what lactose is and what foods commonly contain it, we can begin to understand what lactose intolerance is and why it develops.  In children who are not intolerant, lactose is broken down in the small intestine by an enzyme called lactase, before it gets absorbed into the bloodstream and used for energy by the cells in the body.  If the body for any reason isn’t able to break down or absorb lactose, the child will have something called lactose malabsorption. One of the most common reasons for malabsorption is the lack or insufficient amount of the enzyme lactase in the gut, which limits proper digestion and absorption of lactase.  Some children may have lactose malabsorption but not experience any symptoms.  However, if a child experiences symptoms from lactose malabsorption they can be diagnosed as lactose intolerant (Misselwitz et al., 2019).

Symptoms of lactose intolerance can include any of the following:

  • Bloating (abdominal distention)
  • Diarrhoea (which may be explosive)
  • Flatulence
  • Discomfort and tummy pain
  • Nausea and vomiting
  • Perianal excoriation (sore bottom)

(Clinical Paediatric Dietetics 2020)

How is lactose intolerance diagnosed in children? You may be asked to exclude all lactose-containing foods from your child’s diet for around 2 weeks to see if the symptoms your child is experiencing disappear.  After this, you may slowly start to reintroduce lactose-containing foods back into their diet to see if the symptoms return (Allergy UK National Charity, n.d.).  This should be done under the guidance and support of a dietitian to make sure your child will still be getting enough of the  vital nutrients such as calcium and vitamin D during this period, both of which are important for your child’s development.  In some cases, your child may need clinical testing.

Children who are diagnosed with lactose intolerance will need to avoid lactose-containing products and use lactose-free or low lactose dairy instead. For babies who are lactose intolerant and formula-fed, there are lactose-free formulas available.  These formulas are not suitable for cows’ milk allergy.

It is worth mentioning that lactose intolerance in the newborn is very rare, it is more commonin babies for lactose-intolerance to follow a bout of gastroenteritis and resolves relatively quickly in around 6-8 weeks.


Cows’ Milk Protein Allergy (CMPA)

As milk allergy is something that affects between two to three babies per 100 population in the UK (Anaphylaxis UK, n.d.) it is commonly mentioned but how does it differ from lactose intolerance?

A child has a cows’ milk protein allergy (also known as CMPA) when the body’s immune system attacks against a protein found in milk because it mistakes it as a threat.  (This is different to lactose intolerance where the body struggles to break down and absorb lactose in the gut.)

Symptoms of CMPA can vary from a mild rash to anaphylactic shock in the most severe cases which will require the use of an epinephrine injection.  Each child with CMPA will have an individual allergic reaction to milk and therefore different children will need different treatment responses in the case of an allergic reaction.

Milk protein allergy is divided into two categories which are immediate cow’s milk allergy known as IgE mediated  and delayed cow’s milk allergy known as non-IgE mediated. The former will present symptoms between a few minutes up to two hours and symptoms vary from mild to severe.   A delayed or non-IgE mediated reaction will present symptoms between four to 48 hours after consuming milk (Anaphylaxis UK, n.d.).

Cows mill Allergy symptoms include:

IgE Mediated (usually within minutes and up to 2 hours after ingestion):

  • Urticaria/hives
  • Wheezing
  • Itching or a tingling feeling around the mouth or lips
  • Swelling of the lips, tongue, or throat
  • Coughing or shortness of breath
  • Vomiting
  • Anaphylaxis

   (Edwards and Younus, 2020)

Non IgE mediated (2-72 hours after ingestion):

  • Loose stools which can be green and smelly
  • Tummy pain
  • Bloating
  • Vomiting
  • Eczema
  • Blood and/or mucus in stools
  • Constipation

 (MAP Guideline update 2019)


How is cow’s milk protein allergy diagnosed?  There are multiple ways the possibility of a child having CMPA can be assessed.  If your child is suspected of having a delayed allergy (non IgE) to milk, you may be asked to eliminate all products containing milk from your child’s diet to see if any of their symptoms disappear and then slowly reintroduce them to investigate if the symptoms return.  If an immediate (IgE mediated) allergy is suspected, your child may need a skin prick test or blood test to confirm the diagnosis (, n.d.).   A detailed allergy-focussed history should also be taken and includes questions around severity and timing of symptoms and family history of allergic disease.

Whilst cow’s milk protein allergy is rare it is still the most prevalent food allergy in the UK that affects very young children and babies (Allergy UK, 2022). However, the good news is that around 75% of children will outgrow their allergy to cow’s milk before the age of 6 (Flom and Sicherer, 2019).

If a child is diagnosed with CMPA they will need to avoid all products containing cows’ milk for as long as they have this allergy. Milk is an allergen which is required by law to be written in bold letters in the ingredients list of any food product that contains it.

It is important to consider that milk is often used in products that may not be expected to contain it as an ingredient and therefore it is important to always read the label before giving a child any particular food.  Fortunately, there are a great number of milk-free dairy alternatives nowadays such as soy, almond, oat and pea “milk” which can be made into products such as ice cream, yoghurt, cream so that your child can still enjoy these types of foods safely.

Lactose intolerance and cows’ milk protein allergy differences summarised.

  • As discussed, milk allergy and lactose intolerance are very different conditions with different physiological reasons behind what causes their symptoms.
  • Lactose intolerance is an intolerance to lactose (milk sugar) and doesn’t involve the immune system, whereas, cows’ milk protein allergy is an immune response to the protein in cows’ milk.
  • Children with either condition will need to avoid normal dairy products such as fresh cows’ milk. However, a child with lactose intolerance can consume milk products that are free from or contain small amounts of lactose, whilst a child with milk allergy may need to avoid all dairy products completely if their allergy is severe.
  • Some symptoms for the conditions may be similar like vomiting, diarrhoea, and tummy pain while some symptoms will differ for example a child with lactose intolerance won’t have an anaphylactic shock reaction of hives after drinking milk like a child with CMPA might.

When a child is suspected of having either condition, they will often be asked to go on an elimination diet. However, if they require further clinical testing these methods will differ.



Allergy UK (2022). Cow’s Milk Allergy | Allergy UK | National Charity. [online] Allergy UK | National Charity. Available at:

An update to the Milk Allergy in Primary Care guideline (2019) Adam Fox, Trevor Brown, Joanne Walsh, Carina Venter, Rosan Meyer, Anna Nowak‑Wegrzyn, Michael Levin, Hannah Spawls, Jolene Beatson, Marie‑Therese Lovis, Mario C. Vieira10, and David Fleischer.  Clinical and Translational Allergy

Flom, J.D. and Sicherer, S.H. (2019). Epidemiology of Cow’s Milk Allergy. Nutrients, 11(5), p.1051. doi:

Clinical Paediatric dietetics, (2020) Chapter 15 by Rosan Meyer and Carina Venter, P 317-318 Edited by Vanessa Shaw

Misselwitz, B., Butter, M., Verbeke, K. and Fox, M.R. (2019). Update on lactose malabsorption and intolerance: pathogenesis, diagnosis and clinical management. Gut, [online] 68(11), pp.2080–2091. doi:

Allergy UK | National Charity. (n.d.). Lactose Intolerance. [online] Available at: (n.d.). default – Stanford Children’s Health. [online] Available at:

Anaphylaxis UK. (n.d.). Milk Allergy. [online] Available at:

‌Edwards, C.W. and Younus, M.A. (2020). Cow Milk Allergy. [online] PubMed. Available at:

Medical Disclaimer: The information provided in these blogs are for general informational purposes only. They are not intended to be a substitute for professional/medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health providers with any questions you may have regarding your child’s medical condition.


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