Particular form of severe allergic reaction. If one comes into contact for the first time with a substance to which one is allergic then antibodies are formed against this substance. In an anaphylactic reaction the antibodies are of a particular kind. If one comes into contact with the substance in question again, the IgE antibodies react with the substance within a few minutes, causing an itchy, red skin eruption with lumps (also called hives or urticaria), constriction of the air passages and lowering of the blood pressure. Serious forms af anaphylactic reaction can result in shock. The most common causes are hypersensitivity to penicillin or similar antibiotics and hypersensitivity to insect stings. The best treatment of anaphlaxis is to avoid contact with substances to which one is abnormally sensitive; a doctor should be warned if he is about to prescribe antibiotics. Patients abnormally sensitive to insect stings should carry medicine (antihistamines) with them which can counter an anaphylactic reaction if they are stung.