food allergies: do you know the signs?

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a food intolerance can be unpleasant, but a food allergy is much more serious.

by dave yasvinski

published oct 13, 2022

last updated feb 19, 2025

4 minute read

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4 minute read

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eggs, milk, peanuts and crustaceans are among the most common allergens. getty

a food allergy is a medical condition that occurs when the body’s immune system perceives certain foods as a threat and responds to them by triggering an allergic reaction.

certain substances are considered priority allergens by health canada as they account for around 90 per cent of food allergies in the country and are the ones most likely to induce a severe reaction. this group consists of eggs, milk, mustard, peanuts, crustaceans and mollusks, fish, sesame seeds, soy, sulphites, tree nuts and wheat.

there are two main categories of food allergy, according to food allergy canada: immunoglobulin e (ige) mediated and non-ige mediated. the most commonly encountered food allergens are ige-mediated and occur when symptoms arise from the way in which the immune system’s ige antibodies interact with certain foods. ingesting even small amounts of foods that produce such a response can trigger a life-threatening allergic reaction known as anaphylaxis.

non-ige mediated reactions occur when other parts of the immune system respond to certain foods (and not the ige antibody). this form of allergy usually involves the gastrointestinal tract and results in symptoms that are unpleasant (such as vomiting and diarrhea) but not life-threatening. it is possible to experience both forms of food allergy at the same time.

food allergies are often confused with food intolerance but intolerance is a less serious condition that does not involve a response from the immune system. the best way to handle a food allergy is to avoid trigger foods and seek medical help if you experience an extreme reaction.

symptoms of a food allergy

an allergic reaction to food usually occurs within minutes but can take up to a few hours following exposure. symptoms can range from mild to severe and may differ each time a specific allergen is encountered. symptoms can include:

a skin rash or hives
swelling of the face, lips or tongue
coughing, wheezing or shortness of breath
chest pain or tightness
nausea or vomiting
pain, cramps or diarrhea
pale skin or weak pulse
feeling lightheaded, dizzy or passing out

for some people, certain allergens can trigger a severe reaction known as anaphylaxis that is capable of sending the body into shock or making it difficult to breathe. anaphylaxis can quickly induce life-threatening symptoms, including:

shock and a quick drop in blood pressure
tightening of the airways, a swollen throat or trouble breathing
rapid heartbeat
dizziness or a loss of consciousness

diagnosing a food allergy

doctors consider a number of factors when investigating a food allergy, including a patient’s symptoms and any family history of allergies. a physical examination may be performed to rule out any other conditions. other tests, according to the mayo clinic, can include:

skin prick test: tests the body’s response to certain foods by allowing a small amount of allergen beneath the surface of the skin and looking for a reaction, such as a raised bump.
blood test: measures the levels of the allergen-related antibody ige in the blood.
elimination diet: suspected foods are removed from a patient’s diet one by one and re-added later. this test, which cannot distinguish between true allergies and food sensitivities, can help link symptoms to allergens.
oral food challenge: small but increasing amounts of suspected foods are given to a patient under the supervision of a doctor. foods that do not prompt a reaction may be safely re-added to a patient’s diet.

treating a food allergy

it may not be possible for a patient to completely avoid foods that induce an allergic reaction — even when they are aware of the issue. for minor reactions, antihistamines (prescribed or over the counter) can alleviate some symptoms, such as itching or hives. for severe reactions, however, patients may need to carry an epinephrine auto-injector that contains the medication needed to reverse life-threatening symptoms. it is important for these patients to have two doses on them at all times as allergic reactions may reoccur.

preventing an allergic reaction

the only sure way to prevent an allergic reaction to food is to carefully avoid the allergens that induce the reaction. this can be a difficult process that requires patients to constantly study food labels to ensure they do not come into contact with a problematic ingredient. because many people do not understand the severity of the issue, it will likely be necessary to inform family, friends and caregivers of any special considerations that must be taken when providing food to you or anyone else at risk.

prevalence of food allergies

more than three million canadians report having at least one food allergy, a rate that impacts one in every two households in the country. roughly 500,000 children have a food allergy, with peanut allergies — one of the most common allergens — affecting around 1 in 50 children.

support for food allergies

for more information about food allergies, including steps you can take to reduce the risk of a reaction in you or someone you know, visit food allergy canada.

dave yasvinski is a writer with  healthing.ca

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