Anaphylaxis is a severe, sudden, often fatal bodily reaction to a foreign substance or antigen.

In humans, anaphylaxis is a rare event usually triggered by an antiserum (to treat snake or insect bites), antibiotics (especially immunoglobulin), or wasp or bee stings. Certain foods can also trigger these severe reactions, including seafood (particularly shellfish), rice, potatoes, peanuts, egg whites, raw milk, and pinto beans.

In systemic or system-wide cases, symptoms occur just minutes (or in rare cases weeks) after introduction of the foreign substance and include flushed skin, itching of the scalp and tongue, breathing difficulties caused by bronchial spasms or swollen tissues, vomiting, diarrhea, a sudden drop in blood pressure, shock, and loss of consciousness. Less severe cases, usually caused by nonimmunologic mechanisms, may produce widespread hives or severe headache. These less severe cases are called anaphylactoid reactions. Any anaphylactic reaction must be considered a medical emergency and...