AAIQ   The Association of Allergists and Immunologists of Québec


There is no universal definition for anaphylaxis, but it may be defined as a serious allergic reaction that has a rapid onset and is potentially fatal. It is generally characterized by the appearance of several signs and symptoms involving one or multiple bodily systems.

What is the mechanism of an anaphylactic reaction?

In most cases of anaphylaxis, the reaction occurs when antibodies called IgE antibodies recognize a particular allergen. When these antibodies are in the presence of this allergen, there is an activation of certain cell types (mastocytes, basophils), which leads to the liberation of different inflammatory products that can affect all the organs and systems in the body. This is the reason for the variety of signs and symptoms that may be observed during an allergic reaction.

It is also possible to observe the phenomenon known as a biphasic reaction in the context of anaphylaxis. A second reaction can follow the initial reaction several hours later.

What are the causes of an anaphylactic reaction?

There are many possible triggers for allergic reactions that can lead to anaphylaxis:

* Foods : 8 foods are responsible for 93% of food reactions in children: eggs, peanuts, milk, soy, nuts, fish, shellfish, wheat. The most common causes in older children and adults are: peanuts, shellfish, nuts and fish.
* Medications
* Stinging, venomous insects: wasps and bees
* Latex
* Immunotherapy
* Physical causes: exercise and cold
* Idiopathic: the cause cannot be identified

Foods cause the majority of anaphylactic reactions.

What are the signs and symptoms of an allergic reaction?

A variety of signs and symptoms may be present during an allergic reaction, and these may occur individually or in association with one another. It is important for people known to have dangerous allergic reactions to become familiar with the first signs of a reaction:

* Skin: urticaria, swelling, itching, heat, redness, skin eruptions;
* It is important to note that it is possible to have an allergic reaction in the absence of skin manifestations.
* Respiratory system: wheezing, shortness of breath, suffocation, cough, hoarse voice, pain or pressure in the chest, runny nose, nasal congestion.
* Gastrointestinal system: nausea, vomiting, diarrhea, abdominal pain.
* Cardiovascular system: changing color (pale or blue), decrease in arterial blood pressure, loss of consciousness, state of shock
* Other: sensation of imminent death, anxiety, headache, uterine cramps

Diagnostic criteria help us determine if the reaction is anaphylactic in nature or is a minor allergic reaction. Anyone who has been diagnosed with anaphylaxis should be evaluated by an allergist in order to review the history of the reaction, and to confirm if indeed it matches the description of anaphylaxis, since there are other conditions that may have manifestations similar to those of anaphylaxis. It is also important to see an allergist, since he or she will attempt to identify the possible cause of the reaction and to discuss ways of preventing these reactions in the future. The allergist will also discuss with you the necessary treatment in case of future allergic reactions.

What is the treatment of an anaphylactic reaction?

It is important to discuss this with your allergist, who will go over the steps to follow in case of an allergic reaction.

The number one treatment of an anaphylactic reaction is epinephrine, which must be administered intramuscularly on the external side of the mid-thigh using an auto-injector (Epipen® or AllerjectTM) or with a syringe in the appropriate medical setting. It is possible to give another dose in the 5 to 20 minutes following the initial dose if the situation worsens. If it is an anaphylactic reaction, it is important not to delay the administration of epinephrine.

You must also call 9-1-1 to be taken to the closest hospital. Other medication might be administered after epinephrine: antihistamines, corticosteroids, asthma inhalers...

What risk factors are associated with a more severe reaction?

* Previous history of severe reactions to foods
* Allergy to nuts, peanuts, fish and seafood
* The concomitant presence of asthma (especially if the asthma is not well controlled)
* A delay in the administration of epinephrine after an acute reaction: the patient does not have an auto-injector in his possession or instead treats the reaction only with antihistamines
* Denial of symptoms
* The patient does not check all possible ingredients
* Friends and family members that have not been well versed regarding the reaction and treatment
* Patients taking B-blockers

What measures need to be taken when there is a risk of an allergic reaction?

* Know the triggering factors, their origins, and how to avoid them
* Use epinephrine rapidly when treating a reaction
* The person at risk for anaphylaxis should always carry an epinephrine autoinjector
* Sometimes it is preferable to have on hand more than one dose of epinephrine. This should be discussed with your allergist.
* Review the expiry dates, the indications, and the technique for using your epinephrine autoinjector on a regular basis.
* Wear a medical bracelet that clearly identifies your allergies.
* Call 9-1-1 and go straight to the hospital in case of an allergic reaction.


Simon Hotte, MD FRCPC
(translation: Andrew Moore, MD FRCPC)