What are food allergies?

What are food allergies?

Written by

Lauren Dobischok
6 January, 2023

Medically checked article All HOMED-IQ content is reviewed by medical specialists

Food allergies are a reaction of your body’s immune system after eating certain foods (NHS, 2019). Even a small amount of a certain food can trigger an allergic reaction, causing symptoms that can range from annoying to life threatening. Food allergies are mediated by the immune system, and differ from other food-related conditions like sensitivities or intolerances. 

What is a food allergy?

Food allergies occur when the immune system mistakes a food as a threat or invader, triggering an immune response in an effort to protect the body (Mayo Clinic, 2021). These foods can also be called allergens. During this response, cells are triggered to release immunoglobulin E (IgE) antibodies to neutralize the allergen. When the body is exposed to an allergen, IgE antibodies trigger chemicals such as histamine to be released into the bloodstream. This causes the recognizable symptoms of an allergic reaction, such as itching, hives, or swelling. 

Allergic reactions do not occur the first time that you encounter an allergen. During the first exposure, the immune system recognizes the allergen as a threat and produces specific IgE antibodies against it. This process is called sensitization (More, 2022). The next time you are exposed to the allergen, the immune system will produce IgE antibodies against it, triggering the allergic reaction. 

Symptoms of food allergies

Food allergies usually develop within minutes or a few hours of eating a certain food. Symptoms can range from mild to life-threatening anaphylaxis. Symptoms of food allergies can include:

  • Itching, hives, redness, rash, or eczema
  • Swelling of the lips, eyes, face, tongue, or throat
  • Shortness of breath, wheezing, or difficulty breathing
  • Nausea, vomiting, and abdominal pain
  • Constipation
  • Diarrhea
  • Fainting or dizziness
  • Fatigue
  • Headache

Symptoms of anaphylaxis include:

  • Swelling and constriction of the airways
  • Drop in blood pressure and shock
  • Rapid pulse
  • Dizziness, lightheadedness, or fainting

Source: Mayo Clinic, 2021

Common food allergies

Common food allergies include peanuts or tree nuts, as well as shellfish, wheat, milk, egg, fish, sesame, and soy (FDA, 2023). Many countries require food packaging to highlight common allergens on their ingredients list to make it easier for people with allergies to avoid them. 

Difference between a food intolerance and allergy

Food intolerances can sometimes cause similar symptoms to food allergies, which is why they are often confused. The biggest difference between a food allergy and intolerance is that allergies are mediated by the immune system. Food intolerances do not cause any IgE reaction and may be caused by a lack of certain digestive enzymes (such as lactose intolerance), irritable bowel syndrome, or sensitivity to food additives (Li, 2022). Symptoms from food intolerances are often milder than allergies, and in some cases the individual can consume small amounts of the trigger food without a reaction.

Causes of food allergies

The exact cause of food allergies is not known. Several risk factors have been identified that increase an individual’s risk of developing food allergies.

Risk factors for food allergies

  • Having a sibling or parent that has allergies, asthma, hay fever, hives, or eczema
  • Other allergies, such as to pollen 
  • Age: children are more likely to develop allergies than adults. Some children outgrow their allergies over time
  • Eczema

Source: Mayo Clinic, 2021

Testing for food allergies

Diagnosing a food allergy can be challenging as there is no single test for food allergies available. Most often a combination of allergy tests, symptoms after eating the food, and family history of allergies are needed to make a diagnosis. Testing methods include:

  • Skin prick test: during this test, small amounts of suspected allergens are placed on the skin, usually the forearm or back. Then skin is then pricked with a needle, and areas where a reaction or bump occurs indicate a possible allergy.
  • Blood test: a blood test for allergies measures the level of food-specific IgE antibodies in the blood. This blood is usually taken in a doctor’s office and sent to a laboratory for analysis.
  • Oral food challenge: this test is often performed if it is suspected that someone has outgrown their allergies. Under the supervision of an allergist, small amounts of the allergen food are given at specific time intervals. If there is no reaction, the person may be able to eat the food again. If there is an allergic reaction, it can be managed in a medical setting. 

Source: Mayo Clinic, 2021

Consequences of a food allergy

The consequences of eating a food when you have an allergy are the symptoms that arise shortly after. These symptoms can range from unpleasant (hives, itching, abdominal pain) to life-threatening (anaphylaxis).

What can I do about a food allergy?

If you are diagnosed with a food allergy it is advised to avoid the allergen food completely. If the allergy causes anaphylaxis, this is especially important. This often means checking food labels or speaking to restaurant staff in order to ensure the food you eat does not contain a potential allergen. 


Center for Food Safety and Applied Nutrition. (2023, January 3). Food Allergies. U.S. Food And Drug Administration. https://www.fda.gov/food/food-labeling-nutrition/food-allergies

Food allergy – Symptoms and causes. (2021, December 31). Mayo Clinic. https://www.mayoclinic.org/diseases-conditions/food-allergy/symptoms-causes/syc-20355095

Li, J. (2022, April 21). Food allergy vs. food intolerance: What’s the difference? Mayo Clinic. https://www.mayoclinic.org/diseases-conditions/food-allergy/expert-answers/food-allergy/faq-20058538

More, D. (2022, June 3). Learn Everything You Should Know About Sensitization and True Allergy. Verywell Health. https://www.verywellhealth.com/what-is-sensitization-82988

NHS website. (2021, November 18). Food allergy. nhs.uk. https://www.nhs.uk/conditions/food-allergy/

About the author

Lauren Dobischok

Lauren is a health scientist and science communicator currently living in the Netherlands. Originally from Canada, she completed a Research Master’s in Health Sciences at the Netherlands Institute of Health Sciences at Erasmus University Rotterdam (NIHES) with a specialisation in epidemiology. Prior to her master’s degree, she completed a Bachelor’s degree in Health Sciences at Simon Fraser University. With a background in public health, her goal is to create accurate scientific content that is easy to understand and empowers people to make informed decisions. Within Homed-IQ, Lauren works as a Product Developer and Content Lead, working closely with physicians and scientists on medical devices for Homed-IQ’s new products and written communications.