Anaphylaxis (pronounced anna-fill-axis) is the most serious type of allergic reaction. It can progress very quickly and may cause death without proper medical attention.

An allergen is a substance which can cause an allergic reaction. While food is one of the most common allergens, medicine, insect stings, latex and exercise can also cause a reaction.

For a full list of allergy terms and definitions see our glossary.

Signs & Symptoms

An allergic reaction usually happens within minutes after being exposed to an allergen, but sometimes it can take place several hours after exposure. A reaction can involve any of these symptoms, and a person could have one or more of these symptoms regardless of the allergen:  

• Skin system: hives, swelling, itching, warmth, redness, rash
• Respiratory system (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
• Gastrointestinal system (stomach): nausea, pain/cramps, vomiting, diarrhea
• Cardiovascular system (heart): pale/blue colour, weak pulse, passing out, dizzy/lightheaded, shock
• Other: anxiety, feeling of "impending doom", headache, uterine cramps, metallic taste

The most dangerous symptoms of an allergic reaction are:

• Trouble breathing caused by swelling of the airways (including a severe asthma attack for people who have asthma)
• A drop in blood pressure causing dizziness, light-headedness, feeling faint or weak, or passing out.

  Both can lead to death if untreated

Some Important Things to Keep in Mind 

• Do not ignore early symptoms, especially if you have had a reaction in the past. Always take a possible reaction seriously and act quickly.
• Not every reaction will always look the same; a person can have different symptoms each time.
• Anaphylaxis can occur without skin symptoms or hives.

The 5 Emergency Steps

1. Give epinephrine (e.g. EpiPen®/Twinject®) at the first signs of an allergic reaction.
2. Call 9-1-1 or your local emergency medical services and tell them that someone is having an anaphylactic reaction.
3. Give a second dose of epinephrine in 5-15 minutes IF the reaction continues or gets worse.
4. Go to the nearest hospital right away (ideally by ambulance), even if symptoms are mild or have stopped. The reaction could get worse or come back after using epinephrine. You should stay in the hospital to be observed (generally about 4 hours).
5. Call the emergency contact person (e.g., parent, guardian, spouse).

Anaphylaxis Emergency Plan

Everyone at risk for anaphylaxis should have an anaphylaxis emergency plan with clear instructions on how to treat symptoms and strategies to reduce risks. The plan is usually two pages. The first page is a form with a person's photo and allergy information and the second page has instructions on how to use an auto-injector.

See Anaphylaxis Emergency Plan for a sample form.

Source:  Some information in the Anaphylaxis 101 section are taken from Anaphylaxis in Schools & Other Settings. Copyright © 2005-2011 Canadian Society of Allergy and Clinical Immunology