The WellChild Helpline provides information and advice What is anaphylaxis? Anaphylaxis is a severe allergic reaction which can be life-threatening. The whole body - the airway, breathing and circulation - can become affected very quickly (usually within minutes) after the person has come into contact with an allergen. An allergen is any substance that causes an allergy. What causes anaphylaxis? It is not known why some children develop anaphylaxis and others do not. The...