Food Allergy or Intolerance: What's the Difference and How to Tell Them Apart

Food allergy and food intolerance are different conditions with different mechanisms, although in everyday speech they are referred to by the same word. An allergy is an immune system reaction, while intolerance is a digestive problem. Both the testing and how dangerous the condition may be depend on this difference.

An immune reaction and a reaction without immunity

Food allergy is a state of heightened sensitivity to foods in which adverse reactions are caused by the involvement of immune mechanisms. Most often the allergen is a food protein: the immune system mistakenly identifies it as harmful, and on repeated consumption histamine and other compounds are released that produce symptoms. Intolerance has a different nature: the body cannot break down a certain substance, the immune system is not involved here, so a serious allergic reaction cannot occur. A distinction is made between food hypersensitivity (an altered reaction to foods), food allergy with an immunological mechanism, and non-allergic hypersensitivity.

Most common allergens

Allergy is most often caused by cow's milk, eggs, peanuts, soy, peas and chickpeas, nuts — walnut, almond, hazelnut, pecan, cashew, pistachio, Brazil nut — crustaceans and molluscs, as well as wheat. Allergy is possible to any food, including celery, mustard, sesame and lupin flour in baked goods. The chance is higher if the person or their close relatives have other allergies, asthma or eczema. Carbohydrates, fats and trace elements more often cause pseudoallergic reactions than a true allergy.

Symptoms of allergy and intolerance

Allergy can affect different parts of the body at the same time: itchy skin or rash, swelling of the lips, face and eyes, cough, wheezing, shortness of breath or a hoarse voice, sneezing and a runny nose, nausea, vomiting, abdominal pain, diarrhoea, dizziness. Symptoms appear immediately after eating or after days. Intolerance usually makes itself felt after a few hours: diarrhoea, bloating, gas, abdominal pain; headache, fatigue, nausea, constipation, joint pain, rash are possible. This lasts from a few hours to a few days.

Lactose and gluten

The most common intolerance is lactose intolerance: the body is unable to digest lactose, the sugar in milk and dairy products. Intolerance also occurs to gluten from wheat, rye and barley, as well as to histamine, caffeine, alcohol, sulphites, salicylates, monosodium glutamate, benzoates.

How it is actually diagnosed

The start is a conversation with a doctor and a food and symptom diary. Then the family doctor may refer to an allergist or to a nutrition specialist. The examination includes the following methods (some of them relate to suspected allergy, some to suspected intolerance):

• a skin prick test with a liquid containing the suspected allergen, if allergy is suspected;
• a blood test;
• an elimination diet followed by reintroduction of the food;
• a breath test if lactose intolerance is suspected.

An allergy is most reliably proven by a challenge test; it is carried out by doctors in a hospital setting because of the risk of an anaphylactic reaction. The double-blind challenge test is considered the gold standard.

Tests that give no answers

Home tests that promise to detect food intolerance are not recommended: there is little evidence of their accuracy, and they may also advise eliminating many foods at once, which harms health. Eliminating a food from the diet without the advice of a doctor or dietitian is dangerous: one may not get enough vitamins and minerals, especially those needed by a child for growth.

The lips, mouth, throat or tongue have suddenly swollen; breathing is very fast or difficult; the skin, tongue or lips have turned blue or pale; the person has suddenly become very confused or drowsy; someone has fainted and cannot be woken. Call 103 or 112 immediately.

You should see a family doctor routinely if symptoms of allergy or intolerance recur. This material is for reference and does not replace a doctor's consultation.

This content is for reference and does not replace a doctor's consultation. Medical disclaimer