ANAPHYLACTIC SHOCK

Anaphylaxis is an acute systemic (multi-system) and severe Type I Hypersensitivity allergic reaction in humans and other mammals. The term comes from the Greek words ana (against) and phylaxis (protection). Anaphylaxis occurs when a person or animal is exposed to a trigger substance, called an allergen, to which they have already become sensitized. Minute amounts of allergens may cause a life-threatening anaphylactic reaction. Anaphylaxis may occur after ingestion, skin contact, injection of an allergen or, in rare cases, inhalation.
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Anaphylactic shock n. A severe, sometimes fatal allergic reaction characterized by a sharp drop in blood pressure, urticaria, and breathing [more]Anaphylactic shock - Community and Resources

Noun
1. a severe and rapid and sometimes fatal hypersensitivity reaction to a substance (especially a vaccine or penicillin or shellfish or insect venom) to which the organism has become sensitized by previous exposure
(hypernym) anaphylaxis

noun
sudden allergic reaction to an allergen such as an injection, which can be fatal

A severe and sometimes life-threatening immune system reaction to an antigen that a person has been previously exposed to. The reaction may include itchy skin, edema, collapsed blood vessels, fainting, and difficulty in breathing.