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Understanding the difference between lactose intolerance and cow’s milk allergy

Due to several similarities in their symptoms, lactose intolerance is often confused with cows’ milk allergy (CMA). This can lead to incorrect diagnosis and therefore treatment, which ultimately means continued discomfort and distress for the child and their parents.

This article explains the key differences between these two conditions to help you recognise one from the other.

Understanding intolerance vs. allergy

Food intolerance and allergy are both examples of ‘food hypersensitivity’. This is the umbrella term for non-toxic adverse reactions to foods1.
Food allergy occurs when a food protein interacts with the immune system to cause an allergic response, whereas food intolerance does not involve food proteins and is a non-immune reaction2.

Food intolerance can be caused by either an enzyme deficiency or a pharmacological reaction2.

• Enzyme deficiency
This is when someone does not produce enough of an enzyme that breaks a particular food down, leaving them unable to digest that food properly.

• Pharmacological reaction
Some substances found in foods can cause a pharmacological reaction, e.g. vasoactive amines, caffeine and alcohol.

The causes of lactose intolerance and CMA

Lactose intolerance is caused by the inability to completely digest lactose, the sugar found in all mammalian milk, due to the absence or deficiency of the enzyme lactase in the gut3,4.

The cause of CMA is an immunologic hypersensitivity to one or more of the proteins found in milk5. This means CMA is an allergic reaction, involving the body’s immune system; lactose intolerance does not involve the immune system3,4.

In addition, unlike CMA, where just a tiny amount of milk protein can trigger a reaction, most people with primary lactose intolerance are able to tolerate small amounts of lactose6,7.

The similarities and differences in symptoms

It can be difficult to differentiate between delayed CMA and lactose intolerance, as some symptoms overlap and the terminology used in the literature and in relation to products is inconsistent.

So it is important to be aware that there are other symptoms which can occur with CMA but not with lactose intolerance.

With lactose intolerance, the symptoms are purely gastrointestinal, e.g. abdominal pain, diarrhoea and bloating2,7. But with CMA, symptoms can be gastrointestinal, or they can be respiratory (e.g., wheezing, rhinitis), or skin-related (urticaria) and, in some cases, can lead to anaphylaxis8. Therefore, symptoms from two or more of these organ systems is suggestive of CMA rather than lactose intolerance9.


Although lactose intolerance and CMA can share some similar symptoms, their actual causes are very different. By understanding the differences between food intolerance and allergy, and being aware of CMA-specific symptoms, healthcare professionals can be better prepared to diagnose and treat these conditions more accurately.

The MAP (Milk Allergy in Primary Care) Guideline is the UK’s first, evidence-based guideline focusing on the diagnosis and management of cow’ milk allergy in primary care. Visit cowsmilkallergyguidelines.co.uk to find out more. Alternatively, download a PDF version of the MAP Guideline algorithm.

A Clinical Knowledge Summary on cows’ milk protein allergy in children was also revised in 2015 and gives diagnosis and management information for healthcare professionals10. Visit https://cks.nice.org.uk/cows-milk-protein-allergy-in-children for more information

  1. Johansson S et al. J Allergy Clin Immunol 2004; 113(5):832-36.
  2. Skypala I, Venter C (eds). Food Hypersensitivity. Oxford: Wiley-Blackwell, 2009.
  3. Wright T, Meyer R. Milk and eggs. In: Skypala I, Venter C (eds). Food Hypersensitivity. Oxford: Wiley-Blackwell, 2009. P.117-35.
  4. Heyman MB. Pediatrics 2006;118(3):1279-86.
  5. Hill DJ et al. J Pediatr 1986;109:270-6.
  6. European Food Safety Authority Panel on Dietetic Products, Nutrition and Allergies. EFSA Journal 2010;8(9):1777.
  7. NHS Choices. Lactose intolerance [Online]. 2011. Available at: http://www.nhs.uk/conditions/Lactose-intolerance/Pages/Introduction.aspx [Accessed: April 2013].
  8. Bahna SL. Ann Allergy Asthma Immunol 2002;89(Suppl):56-60.
  9. NICE. CG116 Food allergy in children and young people: full guideline. London: NICE, 2011.
  10. NICE. Clinical Knowledge Summary. Cows’ Milk Protein Allergy in Children. 2015. Available from https://cks.nice.org.uk/cows-milk-protein-allergy-in-children#!topicsummary (accessed Nov 2016)