The difference between food allergy vs. food intolerance.

Are you allergic to something, or is it a food intolerance? Many people experience abnormal reactions after consuming foods that are typically harmless to the human body. These reactions can vary greatly in their severity ranging from mild discomfort and abdominal pain to chronic fatigue, severe rashes, difficulty breathing and in extreme cases anaphylaxis and death.

Clinically, two types of food-related adverse reactions are identified:

  1. Food intolerance
  2. Food allergy

Because of the similarities in some symptoms, the terms ‘food intolerance’ and ‘food allergy’ are often used interchangeably by patients which creates confusion between the two. However, what is clear and non-confusing is the underlying mechanism by which the body reacts to such challenges and the lasting effect on the patient’s health. While food intolerance is due to the body’s inability to properly process or digest the food consumed, food allergy causes the body to generate a very specific immune response to the food in question.

How does food intolerance develop?

Food intolerance relates to trouble digesting foods and is often caused by the lack of certain enzymes needed to digest these foods or some of their components whether naturally occurring or added during processing. A series of symptoms build up in a few hours to several days after the food in question is consumed. If the offending food is consumed for a long period, these symptoms can be aggravated or become chronic.

Typical examples of food intolerance include lactose, fructose, caffeine, salicylates, sulfites, non-celiac gluten intolerance among others.

Known facts about food intolerance

  • Food intolerance can occur in individuals of all ages and may reach as high as 45% of the population with infants and children often showing higher incidence than adults.1
  • Sometimes, the body may be able to accommodate small amounts of the foods that cause intolerance. But when consumption increases dramatically, the body reacts with undesirable symptoms.
  • Food intolerance symptoms are typically felt 30 min after food ingestion and may last up to 48 hours.

How does a food allergy develop?

Food allergy happens when the immune system reacts to a substance in foods, usually a protein. Upon first encounter with the offending food, the immune system detects the presence of the harmful substance(s) and initiates the production of antibodies called immunoglobulins specific to that allergen. Subsequent exposure causes the allergen to bind to the antibodies which in turn triggers a more rapid and aggressive cascade of responses and symptoms ranging from oral inflammation to cramps, nausea, hives, and even respiratory distress. In extreme and rare cases, severe reactions such as anaphylaxis shock can develop which can lead to death.

Commonly known food allergens include cow’s milk, eggs, fish, shellfish, wheat, peanuts, tree nuts, soy, gluten-containing cereals, sesame, lupin, mustard, celery, and sulfur dioxide. From the regulatory standpoint, such components require clear labeling warning the consumer of their presence. Other less known allergens include corn, sesame, dried fruits, mango, and many others.

Known facts about food allergies

  • Typical food allergens are proteins.
  • They affect 5-6% of young children and 3-4% of adults in westernized countries and are estimated to affect 4-8% of the US population.1
  •  Allergy symptoms could appear immediately after ingesting the offending food or several hours later.
  • Food allergies tend to run in families.

Although some food allergies like cow’s milk may be outgrown, those related to nuts and shellfish are lifelong, and people affected should take the necessary precautions to avoid life threatening reactions.

For patients, it is very confusing to self-diagnose whether their food-related unpleasant symptoms are due to food intolerances or allergies. Before going through diet changes, it’s important to seek the advice of an allergist or immunologist. Another good source of reliable information on this subject is to consult organizations such as the American Academy of Allergy, Asthma & Immunology or the American Gastroenterological Association.2,3


  1. Saeed, S.A.; Ali, R.; Ali, S.S.; Ahmad, N.; Basit, A.; Urfy, M.Z. A closer look at food allergy and intolerance. JCPSP 2004, 14 (6), pp. 376–380.
  2. American Academy of Allergy, Asthma & Immunology.
  3. American Gastroenterological Association.

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