AAIQ   The Association of Allergists and Immunologists of Québec

Food Allergy

What is a food allergy?

A food allergy is an adverse reaction to a food that involves the immune system. Because the immune system is implicated in different types of reactions to food, the term "food allergy" has been defined to mean those reactions that occur immediately after eating the food in question and that involve a certain type of antibody, IgE. This is the kind of reaction that we will discuss in this section. Food allergies are more frequent in children than in adults.

Why does one develop a food allergy?

It's not clear why people develop food allergies. They are part of a spectrum of allergic diseases (atopic dermatitis/eczema, allergic rhinitis, asthma). If one member of the family has a food allergy, the other members are at higher risk to develop an allergic disease, but not necessarily the same one. In addition to genetic causes, environmental causes are also suspected but have not yet been well identified.

What are the symptoms of an allergy to food?

The symptoms generally follow rapidly after eating the particular food. They may involve many systems. Some examples of symptoms are as follows:

-Skin: redness, itching, hives (urticaria), swelling
-Respiratory tract: nasal congestion, sneezing, voice changes, cough, difficulty breathing, wheezing
-Digestive system: itching or swelling in the mouth, difficulty swallowing, nausea, vomiting, abdominal pain, diarrhea
-Cardiovascular system: weakness or low blood pressure

When the symptoms are severe and involve 2 systems, this is called anaphylaxis. Sometimes the symptoms are severe enough to cause death.

What are the causes of food allergy?

The foods most commonly responsible include milk, eggs, peanuts, nuts, fish, seafood, soya and wheat. Even though they can be diagnosed during childhood, allergies to peanuts, nuts, fish and seafood are the most common food allergies in adults.

How does one diagnose a food allergy?

The diagnosis rests substantially on the history. In effect, symptoms occurring in direct relation to the ingested food permit the allergist to focus his or her testing. It is important to note all the ingredients consumed before a reaction (and afterwards) as well as the timing of the symptoms. If the reaction occurred outside the home, it is important to question those responsible for preparing the meal. The allergist uses the history to decide which tests to use, because tests performed without a clear history are difficult to interpret.

Once the history is established, skin prick tests are performed on the forearm to different food extracts. Sometimes the allergist decides to perform skin tests with fresh food (especially fruits and vegetables), again on the forearm. Check with your allergist if you need to bring the suspected food to the appointment. According to the skin test results, and sometimes to follow the allergy, the doctor will request a blood test to measure specific IgE levels in the blood. Finally, in order to confirm the absence or the disappearance of an allergy, an oral provocation test (or challenge) may be needed. In this case, you will eat the food in question in several steps under medical supervision.

What is the natural evolution of food allergies?

The majority of children with allergies to milk, eggs, soya and wheat will see a resolution of their allergy, often before school age. In the case of peanuts (and possibly nuts), the chances of resolution are much less, approximately only 20% according to certain studies. Few data exist regarding the resolution of allergies to other foods.

What is the treatment of a food allergy?

The principal and most important treatment is avoidance. You must read all ingredients, inform those around you and don't hesitate to question the possible presence of a food allergen. You must pay attention when cooking so as not to contaminate utensils and food preparation surfaces with the food allergen when an allergic person is sharing a meal with others.

It is recommended to carry an autoinjector of epinephrine (eg: Epipen®) at all times because accidental exposures may occur. In these cases the rapid administration of epinephrine can save a life when symptoms are present. After injecting epinephrine, it is recommended to call for an ambulance or to present rapidly to the emergency room. It is important to know how to use an epinephrine autoinjector and to regularly check the expiry date.

In addition, it is often recommended to wear a medical bracelet informing others of the allergic condition in case of emergency. Many new treatments, among others, treatments involving desensitization, are presently being studied. For more information on food oral desensitization, you may consult this link or speak with your allergist.


Nha Uyen Nguyen-Luu, MD FRCPC
(translation: Andrew Moore, MD FRCPC)