Signs & symptoms

Signs and symptoms of a severe allergic reaction can occur within minutes of exposure to an allergen.

In rarer cases, the time frame can vary up to several hours after exposure.

The way these symptoms can vary from person to person and even from episode to episode in the same person.

An anaphylactic reaction can involve any of the following symptoms, which may appear alone or in any combination, regardless of the triggering 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

Because of the unpredictability of reactions, early symptoms should never be ignored, especially if the person has suffered an anaphylactic reaction in the past.

It is important to note that anaphylaxis can occur without hives.
If an allergic person expresses any concern that a reaction might be starting, the person should always be taken seriously. When a reaction begins, it is important to respond immediately, following instructions in the person’s Anaphylaxis Emergency Plan. The cause of the reaction can be investigated later.

The most dangerous symptoms of an allergic reaction involve breathing difficulties caused by swelling of the airways (including a severe asthma attack in those who have asthma) or a drop in blood pressure indicated by dizziness, lightheadedness, feeling faint or weak, or passing out. Both can lead to death if untreated.

For a description of how young children might describe the signs and symptoms of anaphylaxis, see

Updated March 01, 2010
Association qubcoise des allergies alimentaires The Canadian Allergy, Asthma and Immunology Foundation Anaphylaxis Canada CSACI Allergy/Asthma Information Association 2011 Guidelines Anaphylaxis Emergency Plan