Many people ask us the same question: what’s the difference between an allergy and an intolerance? The terminology for allergies and intolerances is frequently used interchangeably. But this is incorrect, as allergies and intolerances are completely different. This is particularly relevant when discussing a milk allergy, milk intolerance and lactose intolerance.

The Difference Between Allergies and Intolerances

Whilst milk allergies, milk intolerances and lactose intolerance can result in similar symptoms, they are not the same. Milk allergies and intolerances are immune-mediated and can be identified through blood testing, while lactose intolerance is enzyme-mediated. This means that lactose intolerance symptoms occur due to an insufficiency of the digestive enzyme lactase and in this case, a breath test is required.

Immune mediated responses are reactions to a specific substance where the body produces antibodies [1] (IgE & IgG, for example) to fight against proteins in the item it’s reacting to.

An allergy can be life-threatening [2], while an intolerance can be nauseating and consistent. So, if you are suffering from headaches, constant fatigue and are feeling nauseous on a regular basis, then you may have an intolerance to milk or lactose. Allergies can cause much more severe symptoms that usually occur much more rapidly than those cause by an intolerance.

Lactose Intolerance

Lactose intolerance is an inability to break down the sugar element, lactose, in the milk due to an insufficiency of the enzyme lactase [3]. There is an inability within the body to break down and absorb the lactose often results in the production of gases, hydrogen and methane. In turn, these gases are exhaled, so levels can be tested to identify the condition.

With lactose intolerance, it is not always necessary to remove all milk products, this is because certain milk products, such as aged hard cheese, butter or probiotic-rich plain yoghurt have very little lactose in them, but this depends upon the severity of your lactose intolerance.

Symptoms of lactose intolerance include;

  • Excessive gas
  • Diarrhoea
  • Bloating
  • Feeling sick
  • Stomach cramps or pains


Milk Allergy

A milk allergy is where an allergic reaction occurs after consumption of (or contact with) milk or milk products. Unlike an intolerance, this reaction can be life-threatening, especially if not treated quickly. It is recommended that those with a milk allergy eliminate all milk products from your diet on an on-going basis.

A milk allergy can be tested for in various ways, such as skin prick testing or a blood sample test. Blood sample tests check for the antibody ‘IgE’ in response to milk [4]. These samples can conveniently be taken at home and posted to a lab for analysis.

Symptoms of a milk allergy include;

  • Itchy, water eyes (often red)
  • Tight chest
  • Hives
  • Swelling of the lips, tongue, eyes, or face
  • Vomiting
  • Diarrhoea


Milk Intolerance

In the case of milk intolerance, your results may indicate that you are intolerant to certain milk products but not others, for example, milk but not cheddar cheese. This is due to the differing levels of proteins and bacteria in the various milk products. Milk intolerance can be identified through blood sample testing, where the sample is analysed for IgG antibodies in response to milk [5].

An initial period of elimination of 4 weeks is recommended, following this you may be able to successfully reintroduce the items however this is an individual preference. Many people choose to continue abstinence or a reduction in their intake of milk products as they feel better for it.

Symptoms of milk intolerance include;

  • Bloating
  • Constipation
  • Fatigue
  • Headaches or migraines
  • Nausea
  • Skin rashes and eczema
  • Diarrhoea


Differentiating them all

In summary, are some crucial differences between the three conditions. Milk allergy and milk intolerance are Lactose intolerance is an insufficiency of the enzyme lactase resulting in the inability to break down the milk’s sugar and can be tested for using a breath test. If you suspect your symptoms relate to a milk allergy or milk intolerance, then testing may be the only method to accurately determine which, if any, of these conditions you may have.



[1] Justiz, A.A. and Kamleshun Ramphul (2020). Immunoglobulin. [online] Available at: [Accessed 5 Mar. 2020].

[2] (2017). Allergies: Overview. [online] Available at: [Accessed 6 Mar. 2020].

[3] Malik, T.F. and Panuganti, K.K. (2019). Lactose Intolerance. [online] Available at: [Accessed 6 Mar. 2020].

[4] Waserman, S., Bégin, P. and Watson, W. (2018). IgE-mediated food allergy. Allergy, Asthma & Clinical Immunology, [online] 14(S2). Available at: [Accessed 5 Mar. 2020].

[5] Lin, S., Yang, X., Xing, Y., Wang, X. and Li, Y. (2019). The Clinical Application Value of Multiple Combination Food Intolerance Testing. Iranian journal of public health, [online] 48(6), pp.1068–1073. Available at: [Accessed 5 Mar. 2020].