A rapid allergic reaction that can be life-threatening. Anaphylaxis is an acute systemic type of allergic reaction that affects the entire body. During an anaphylactic reaction, the immune system releases antibodies and the tissues release substances such as histamine, which causes the airways to narrow, resulting in wheezing and labored breathing. Histamine also causes the blood vessels to dilate, or widen, which leads to a drop in blood pressure, resulting in shock. Hives often occur, and irregular heartbeats (arrhythmias) can occur during prolonged reactions.
The response that takes place during anaphylactic shock.