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Lactose intolerance versus milk allergy: What’s the difference?

abdominal pain

Not many people know this, but lactose intolerance is not the same as a milk allergy – although they may sound the same. Lactose intolerance is not dangerous, but a milk allergy could be life-threatening. Read on to learn more about this modern-day conundrum.

lactose intolerance
Lactose intolerance and milk allergy are not the same thing.

What is lactose intolerance?

Lactose intolerance is an issue of the digestive system that occurs when an individual’s small intestine does not produce or does not produce enough lactase – an enzyme necessary for the breakdown of lactose. Lactose is a type of sugar specifically found in milk and other dairy products like chocolate, yoghurt, cheese, ice cream, and butter.

Digesting lactose does not pose any problem for most people because lactase breaks down lactose into glucose and glycogen, which are then absorbed into our bloodstream and transported to all body parts to be used as energy.

For people who are lactose intolerant, lactose cannot be broken down, so it travels down to the colon, where it gets fermented by bacteria, resulting in bloating, diarrhoea, and abdominal cramps.

Fortunately, although lactose intolerance is inconvenient and, at times, embarrassing, it is not a life-threatening condition.

What are the causes of lactose intolerance?

We already know that lactose intolerance is caused by insufficient or a complete lack of lactase. But why do some individuals lack this enzyme?

  • Congenital lactase deficiency: some individuals may produce little or no lactase since birth.
  •  Injury: some medical conditions, such as Crohn’s disease or coeliac disease, cause injury or damage to the small intestine, resulting in reduced lactase production.
  • Lactase nonpersistence: this occurs when the small intestine slows down lactase production as time goes by — this is why some people only develop lactose intolerance when they are adults.
  • Premature birth: the small intestines in babies born prematurely may not produce enough lactase initially. This condition is known as transient lactose intolerance as it usually corrects itself as the baby grows older.
premature baby
Premature babies have been found to be more prone to lactose intolerance than full-term babies.

What are the symptoms of lactose intolerance?

Symptoms of lactose intolerance usually appear 30-60 minutes after consuming dairy products; symptoms include:

  • Bloating
  • Diarrhoea
  • Abdominal cramping
  • Gassiness
  • Nausea
  • Vomiting
  • Gurgling or rumbling in the stomach

The severity of symptoms depends on two things:

  • How much dairy was consumed
  • How well your body can tolerate lactose (based on whether your body produces lactase at all or whether your body produces insufficient lactase)

These symptoms are brief and will be alleviated once the dairy products have been removed from your digestive system.

What is a milk allergy?

A milk allergy, like all types of allergies, is an issue of the immune system where the body over-reacts to one or more proteins present in milk and other dairy products. This results in an allergic reaction with symptoms ranging from mild (rashes) to severe/life-threatening (anaphylactic shock).

Milk allergies can affect anyone but are one of the most common allergies in children and babies, affecting approximately 0.5-2.5% of children [1],[2],[3],[4]. Milk allergies usually occur in response to dairy products that contain cow’s milk.

milk allergy
Milk allergy is an allergy to dairy products that contain cow’s milk.

What are the causes of a milk allergy?

For individuals with a milk allergy, their immune system recognises one or more proteins in milk as a foreign invader. As a response, the immune system releases the antibody – immunoglobulin E (IgE), which then signals the body to release histamine and other chemicals responsible for the allergic symptoms.

Two proteins in cow’s milk can trigger an allergic reaction:

  • Whey: the liquid that remains when milk curdles.
  • Caesin: the solid part of milk when it curdles and the most common trigger of milk allergies.

Your likelihood of developing a food allergy such as a milk allergy significantly increases if one or both of your parents have allergies to food or other particles [5].

Types of milk allergies and their symptoms

 lgE-mediatedNon-IgE mediated
What is itIgE is an antibody the immune system produces when it recognises milk protein as a foreign invader. It causes immediate symptoms.Involves other aspects of the immune system other than IgE. Symptoms develop later and are usually confused with the symptoms of lactose intolerance.
SymptomsRashes or hivesWheezingCoughingBreathlessnessItching around the mouthSwelling of the lips, mouth, or tongue VomitingAbdominal crampsRunny noseWatery eyesDiarrhoea (may contain blood)Colic

Do I have lactose intolerance or a milk allergy?

Apart from identifying your symptoms, diagnostic tests must be carried out to confirm if you have lactose intolerance or a milk allergy.

abdominal pain
Testing must be conducted to identify whether your symptoms are due to lactose intolerance or a milk allergy.

Tests for lactose intolerance include:

  • Hydrogen breath test: a hydrogen breath test measures the amount of hydrogen in your breath after consuming dairy products. Elevated hydrogen levels in your breath may suggest digestive issues like lactose intolerance.
  • Lactose intolerance test: your blood sugar level is measured after consuming dairy products. Your blood sugar level will not rise if you have lactose intolerance since your body cannot break down lactose into glucose and glycogen which are then absorbed by the bloodstream.
  • Genetic testing: tests for any genetic causes of lactose intolerance.
  • Stool acidity test: most commonly used for babies where the acidity levels of their stool are tested. A lower pH level (more acidic) signals lactose intolerance.
  • Lactase activity at the jejunal brush border: this is an invasive but accurate test involving a biopsy of the jejunal brush border – part of your small intestine.

Tests for a milk allergy include:

  • Blood test: a blood sample will be taken and sent to a laboratory. Milk proteins are then introduced to your blood sample, and the levels of IgE are measured. High levels of IgE present signals a milk allergy.
  • Skin prick test: a part of your skin will be cleaned and pricked with a small amount of fluid containing milk proteins. After 15 minutes, the test area is examined to check for any skin discolouration, raised skin, or itchy skin. A reaction signals a milk allergy.
  • Graded oral challenge: a small amount of milk is ingested in a controlled environment. Your doctor will examine you for an allergic reaction.


Lactose intolerance and milk allergy are different, even down to the way each one is diagnosed. Lactose intolerance is a digestive system issue, while milk allergy is an immune system issue. The former is not life-threatening, while the latter can be.

Fortunately, both can be treated, and symptoms can be avoided simply by steering clear of dairy products. It is essential to get properly tested so you can live comfortably and healthily.


  1. Julie D Flom, S. H. (2019). Epidemiology of Cow’s Milk Allergy. Nutrients, 1051.
  2. AA Schoemaker, A. S.-P. (2015). Incidence and natural history of challenge-proven cow's milk allergy in European children--EuroPrevall birth cohort. Allergy, 963-972.
  3. Junichiro Tezuka, 1. M. (2021). Possible association between early formula and reduced risk of cow’s milk allergy: The Japan Environment and Children’s Study. Clinical and Experimental Allergy, 99-107.
  4. Rachel L Peters, J. J.-L. (2018). The Prevalence of Food Sensitization Appears Not to Have Changed between 2 Melbourne Cohorts of High-Risk Infants Recruited 15 Years Apart. The Journal of Allergy and Clinical Immunology in Practice, 440-448.
  5. Kanika Kanchan, S. C. (2021). Current insights into the genetics of food allergy. The Journal of Allergy and Clinical Immunology, DOI:https://doi.org/10.1016/j.jaci.2020.10.039.
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