Allergy

An allergy is an excessive or hypersensitive response of the immune system. The allergic reaction becomes manifest as a pathological immune reaction induced either by antibodies (immediate hypersensitivity) or by lymphoid cells (delayed type allergy). Instead of fighting off a disease-causing foreign substance, the immune system launches a complex series of actions against an irritating substance, referred to as an allergen. The symptoms of an immediate hypersensitivity begin shortly after contact and decay rapidly, while the delayed type symptoms do not reach their maximum for 24–48 The allergic response. Illustration by Hans & Cassidy. Courtesy of Gale Group. hours and decline slowly over a period of days or weeks. An allergic reaction may be accompanied by a number of stressful symptoms, ranging from mild to severe to life threatening. In rare cases, an allergic reaction can lead to anaphylactic shock—a condition characterized by a sudden drop in blood pressure, difficulty in breathing, skin irritation, collapse, and possible death.

The immune system may produce several chemical agents that cause allergic reactions. The main group of immune system substances responsible for the symptoms of allergy includes the histamines, which are produced after an exposure to an allergen. Along with other treatments and medicines, the use of antihistamines helps to relieve some of the symptoms of allergy by blocking out histamine receptor sites. The study of allergy medicine includes the identification of the different types of allergy, immunology, and the diagnosis and treatment of allergy.