Symptoms can occur within minutes or up to two hours after contact with the allergy-causing substance but, in rare instances, may occur up to four hours later. Anaphylactic reactions can be mild to life-threatening, so medical assistance should be sought immediately.

Who is at risk for having an anaphylactic reaction?

Anyone with a previous history of anaphylactic reactions is at risk for another severe reaction. Individuals with food allergies (particularly allergies to shellfish, peanuts and tree nuts) and asthma may be at increased risk for having a life-threatening anaphylactic reaction. A recent study showed that teenagers with a food allergy and asthma appear to be at highest risk of a reaction because they are more likely to eat away from home, they are less likely to carry medications and they may ignore or not recognise symptoms.

What are the symptoms of an anaphylactic reaction?

An anaphylactic reaction may begin with a tingling sensation, itching or a metallic taste in the mouth. Other symptoms can include hives, a sensation of warmth, asthma symptoms, swelling of the mouth and throat area, difficulty breathing, vomiting, diarrhoea, cramping, a drop in blood pressure and loss of consciousness. These symptoms may begin in as little as five to 15 minutes or up to two hours after exposure to the allergen, but life-threatening reactions may develop progressively over several hours.

Some individuals have a reaction and the symptoms go away only to return two to three hours later. This is called a ‘biphasic reaction’. Often the symptoms occur in the respiratory tract and take the individual by surprise.