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What are food allergies?

According to the National Institute of Allergy and Infectious Diseases (NIAID), a food allergy is “an adverse health effect arising from a specific immune response that occurs reproducibly on exposure to a given food.”1 A food allergy can affect the body’s respiratory, skin, and gastrointestinal systems, and cause inflammation, itching, diarrhea, and vomiting. In some cases, food allergies can trigger anaphylaxis, a severe allergic reaction characterized by tightening of the airways, difficulty breathing, and loss of consciousness. Without prompt treatment, anaphylaxis can cause death. The most common food allergy triggers are eggs, milk, peanuts, tree nuts, wheat, shellfish, and soy.1,2

Food allergies can be mistaken for food intolerances. Unlike allergies, food intolerances do not involve an immune system response. Instead, a food intolerance involves difficulty digesting or metabolizing a particular food. Most of these symptoms take place in the gastrointestinal tract and include gas, bloating, abdominal pain, and diarrhea.1

Food allergies have increased in the last 2-3 decades, affect mostly industrialized countries, and are more common in children than adults. In 2014, 8% of children and 5% of adults in the US had a food allergy.2

What are common symptoms?

Food allergies are split into two categories – Immunoglobulin E (IgE) mediated allergies and non-IgE-mediated allergies – depending on how quickly the immune system responds to the allergen.3

IgE-mediated allergies have an immediate (less than 2 hours) reaction to an allergen and only require a small quantity of food for a reaction. Possible reactions include3:

  • Skin rashes and hives
  • Oropharyngeal symptoms: itchiness, irritation, and mild swelling of the lips, tongue, palate, and throat
  • Respiratory tract symptoms: coughing, nasal discharge, and impaired breathing
  • Gastrointestinal symptoms: nausea, abdominal pain, abdominal cramping, vomiting, and/or diarrhea
  • Anaphylaxis: severe and rapid allergic reaction that can cause death if not immediately treated

Non-IgE-mediated (or cell mediated) allergies take about 4-6 hours and require more of the food allergen for a reaction. While the allergy does involve an immune reaction, it doesn’t involve IgE antibodies and is generally limited to the gastrointestinal tract. These reactions are mostly subacute and/or chronic, and include3:

  • Food protein-induced inflammation in the entire gastrointestinal tract, or in certain sections (small bowel, rectum, or colon)
  • Food-induced pulmonary hemosiderosis (also known as Heiner syndrome)
is an antibody found in mammals that has an essential role in allergic reactions, including asthma, rhinitis, and dermatitis.
is the overaccumulation of iron in the form of hemosiderin (iron storage in cells) in the lungs.

What are the causes?

IgE-mediated allergies are the more common type of food allergy. When an individual with a food allergy ingests the allergen, IgE activates the immune response and triggers an intense inflammatory (allergic) reaction in cells that are in the presence of the allergen. The mechanisms of a non-IgE-mediated allergic reaction, however, are still not clearly understood. Non-IgE-mediated sensitization to food allergens can occur in the gastrointestinal tract, skin, and the respiratory tract.2,4

Risk factors for food allergies can be genetic and environmental. Genetic factors associated with increased food allergy risk are2:

  • Male sex
  • Asian and African genetic ancestry
  • Family history
  • Specific genes

Environmental risk factors during early life have the greatest impact on food allergies and suggest that a lack of microbial exposure drives allergic diseases. The factors that lower food allergy risk include (in order of relevancy)5,6:

  • Natural birth
  • Breastfeeding
  • Having older siblings
  • Attending daycare in early life
  • Exposure to furry animals

Other environmental factors associated with increased food allergy risk include2:

  • Atopic diseases (asthma, dermatitis, rhinitis)
  • Increased hygiene
  • Obesity
  • Poor diet
  • Vitamin D insufficiency

How does this topic relate to my microbiome?

Most environmental risk factors for food allergies are related to the composition of the intestinal microbiome. Several studies suggest that a dysbiotic gut microbiota increases the production of IgE, leading to a heightened immune response.5 The microbiota may also influence a person’s susceptibility to certain food triggers by producing proteins that can strengthen the intestinal barrier and supporting protective mechanisms in the body’s immune response. However, there is no conclusive data suggesting a strong relationship between the microbiota and food allergies.5,7,8

Which diseases/topics are related to food allergies?

Food allergies can trigger and aggravate the following diseases1:

  • Asthma
  • Atopic dermatitis
  • Eosinophilic gastrointestinal disorders
  • Exercise-induced anaphylaxis
are a group of disorders that affect the gastrointestinal tract. They occur when a type of white blood cell called an ‘eosinophil’ accumulates in the GI tract, triggering inflammation and tissue damage.

How can I take action?

The first step in managing a food allergy is to avoid consuming the food that’s causing the allergy. This includes being aware of situations in which the food you’re eating may have come in contact with a food you are allergic to. Sometimes, ingredients can be hidden in foods, so you should always read the ingredient list of packaged foods and ask before ordering in restaurants. If you are breastfeeding and your child is allergic to a certain food, you should also avoid eating that food.3

For more details about how to manage allergic reactions, particularly in an emergency, consult your healthcare provider. They may suggest taking antihistamines to lessen your symptoms. Always carry an allergy shot (EpiPen) in case of emergencies, depending on the severity of your allergic reaction and your age.3,5


1. Boyce, J. A., Assa’ad, A., Burks, A. W., Jones, S. M., Sampson, H. A., Wood, R. A., … Schwaninger, J. M. (2010). Guidelines for the Diagnosis and Management of Food Allergy in the United States: Summary of the NIAID-Sponsored Expert Panel Report. Journal of Allergy and Clinical Immunology, 126(6), 1105–1118.

2. Sicherer, S. H., & Sampson, H. A. (2018). Food allergy: A review and update on epidemiology, pathogenesis, diagnosis, prevention, and management. Journal of Allergy and Clinical Immunology, 141(1), 41–58.

3. National Academies of Sciences, Engineering and Medicine (2017). Finding a Path to Safety in Food Allergy. (V. A. Stallings & M. P. Oria, Eds.). Washington, D.C.: National Academies Press.

4. Vighi, G., Marcucci, F., Sensi, L., Di Cara, G., & Frati, F. (2008). Allergy and the gastrointestinal system. Clinical and Experimental Immunology, 153(SUPPL. 1), 3–6.

5. Blázquez, A. B., & Berin, M. C. (2017). Microbiome and food allergy. Translational Research, 179(1), 199–203.

6. Marrs, T., Bruce, K. D., Logan, K., Rivett, D. W., Perkin, M. R., Lack, G., & Flohr, C. (2013). Is there an association between microbial exposure and food allergy? A systematic review. Pediatric Allergy and Immunology, 24(4), 311–320.e8.

7. Molloy, J., Allen, K., Collier, F., Tang, M. L. K., Ward, A. C., & Vuillermin, P. (2013). The potential link between gut microbiota and IgE-mediated food allergy in early life. International Journal of Environmental Research and Public Health, 10(12), 7235–7256.

8. Prince, B. T., Mandel, M. J., Nadeau, K., & Singh, A. M. (2015). Gut Microbiome and the Development of Food Allergy and Allergic Disease. Pediatric Clinics of North America, 62(6), 1479–1492.