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