Food allergy FAQs

1. What is a food allergy?

The immune system normally protects a person from germs and disease. It helps them to fight off bacteria, viruses, and other tiny organisms that can make them sick. If someone has a food allergy, their immune system mistakenly treats something in a particular food (most often, the protein) as if it’s dangerous to them. Their body reacts to the food by having an allergic reaction.

2. How does a food allergy differ from a food intolerance?

A food allergy involves the immune system and symptoms can be life-threatening. A food intolerance is the inability to digest or absorb certain foods. For example, someone with lactose intolerance doesn’t have enough of the enzyme lactase to break down the sugar (lactose) in dairy products. The symptoms of food intolerance affect the gastrointestinal tract and can cause discomfort but are generally not life-threatening.

3. What are the priority food allergens in Canada?

Health Canada defines the priority food allergens as: peanut, tree nuts, sesame, milk, egg, fish, crustaceans (e.g., lobster, shrimp) and molluscs (e.g., scallops, clams), soy, wheat and triticale, and mustard. A person can be allergic to any food, but these are the most common. Health Canada’s food labelling regulations require the inclusion of the common name of these priority allergens as well as gluten sources and added sulphites on a food label. Read more about the priority food allergens.

4. What is anaphylaxis?

Anaphylaxis (pronounced anna-fill-axis) is a serious allergic reaction that is rapid in onset and may cause death. Individuals who have IgE mediated food allergy and are at risk of anaphylaxis should carry an epinephrine auto-injector (e.g. EpiPen^®) which contains life-saving medication to treat an allergic reaction. At present, tests cannot tell us how severe a person’s reaction will be.

5. What are the symptoms of anaphylaxis?

Symptoms of anaphylaxis generally include two or more of these body systems: skin, respiratory, gastrointestinal, cardiovascular.

• Skin: hives, swelling (face, lips, tongue), itching, warmth, redness
• Respiratory (breathing): coughing, wheezing, shortness of breath, chest pain/tightness, throat tightness, hoarse voice, nasal congestion or hay fever-like symptoms (runny, itchy nose and watery eyes, sneezing), trouble swallowing, choking feeling
• Gastrointestinal (stomach): nausea, pain/cramps, vomiting, diarrhea
• Cardiovascular (heart): paler than normal skin colour/blue colour, weak pulse, passing out, dizziness or lightheadedness
• Other: anxiety, sense of doom (the feeling that something bad is about to happen), headache, uterine cramps, metallic taste

Breathing or heart symptoms alone can be anaphylaxis. Keep in mind that hives don’t always appear during anaphylactic reactions.

6. What causes anaphylaxis?

Food is one of the most common causes of anaphylaxis, but insect stings, medications, latex, and exercise can also cause reactions. Learn more about the non-food allergens.

7. How fast can a reaction to a food occur?

Most allergic reactions happen within minutes, but some can occur a few hours after exposure.

8. How much of a food allergen does it take to cause a reaction?

Even a small amount of an allergen transferred to a serving utensil has the potential to cause a severe allergic reaction. It’s important to know how to avoid cross-contamination.

9. Can someone have a reaction without ingesting their allergen?

For most people, accidentally eating a food containing their allergen poses the greatest risk. Allergic reactions to foods are caused by specific food proteins. Since food odours do not contain protein, they cannot cause reactions. People can have reactions when they inhale food proteins to which they are allergic, such as in the steam produced while cooking certain foods, like fish.

10. Can someone who is allergic to a food have an allergic reaction after kissing someone who has eaten that food?

Yes. People at risk need to tell their friends and partners about their food allergies to avoid accidental exposure, as small amounts of food can be transferred from one person to another through kissing.

11. How are allergic reactions avoided?

Reading ingredient labels on foods, taking special precautions in food preparation and ensuring proper hand washing and cleaning go a long way toward reducing the risk of an accidental exposure. Learn more about how to avoid reactions.

12. How is anaphylaxis treated?

Epinephrine is first-line treatment for anaphylaxis, and epinephrine auto-injectors (e.g. EpiPen^®) contain a pre-measured dose of the medication. Antihistamines and asthma medications shouldn’t be used instead of epinephrine for treating anaphylaxis, but can be given as secondary medications. After receiving epinephrine, a person should go to hospital, ideally by ambulance, for observation and/or further treatment. Learn more about emergency treatment.

13. Why do so many people seem to have food allergy these days?

There is no easy explanation to explain the prevalence of food allergy. One theory, known as the “dual-allergen exposure hypothesis” suggests that initial exposure to food allergens through the skin, especially in babies with eczema, can lead to allergy while oral exposure (eating the food) can lead to tolerance. Another theory, the “hygiene hypothesis”, suggests that people in Western countries are living in cleaner and more sanitized environments, and their immune systems are shifting toward developing allergic responses to certain foods and away from fighting germs or infections.

The risk factors for food allergy include:

• Age: Food allergy is more common in young children than in older children or adults.
• Family history: You’re more likely to have a food allergy if your parent or sibling has one.
• Another food allergy: If you have a food allergy, you’re at greater risk for developing another.
• Related medical conditions: Your risk is increased if you have an allergic disease such as asthma, eczema, or hay fever.

14. Can food allergy be prevented?

There is evidence that the early introduction of some allergenic foods and maintaining regular ingestion
can prevent the development of allergy in most high-risk children. In 2019, the Canadian Paediatric Society (CPS) released updated recommendations on the specific timing of early introduction of allergenic
foods for high-risk infants. The new guidance is to actively offer non-choking forms of foods containing
common allergens (e.g. peanut, egg) around 6 months of age, but not before 4 months. In 2021, the CPS and CSACI strengthened these recommendations in an updated position statement, including recommending introduction at around 6 months of age for low risk infants. In 2023, the CSACI additionally reinforced the importance of regular ingestion as a means of food allergy prevention.

Learn more about preventing food allergy and early introduction of allergens.

15. Can a food allergy be outgrown?

Allergies to peanut, tree nuts, and shellfish (crustaceans and molluscs) tend to be lifelong. Some allergies, such as milk and egg, can be outgrown by school age.

16. How is food allergy treated?

Currently treatments exist that can desensitize an individual to their allergen which means it increases the amount of allergen tolerated and therefore reducing their risk of reactions. There are different methods of delivery including oral immunotherapy (OIT), epicutaneous immunotherapy (EPIT) and sublingual immunotherapy (SLIT) with mainly OIT having access in Canada at this time. Additionally, the FDA has approved omalizumab, a biologic, to reduce the risk of reactions, but this has not yet been approved in Canada. These therapies are potential treatments for some patients with food allergy. Learn more about these therapies.