What is anaphylaxis?

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Anaphylaxis is a severe, rapid-onset systemic hypersensitivity reaction driven by IgE-mediated activation of mast cells and basophils. When a previously sensitized person encounters the triggering antigen, IgE antibodies on mast cells cross-link and trigger degranulation, releasing mediators such as histamine, leukotrienes, and prostaglandins. This causes widespread vasodilation and increased vascular permeability (leading to a drop in blood pressure and swelling), plus bronchoconstriction and airway edema that can make breathing very difficult. Because it can involve multiple organ systems at once and progress quickly to shock, it is a medical emergency requiring prompt epinephrine administration and supportive care. The other descriptions don’t fit the rapid, systemic IgE-mediated mechanism: a mild local reaction is limited to one area, a delayed type hypersensitivity is T-cell–mediated and slower, and IgG autoantibodies point to autoimmune processes rather than acute anaphylaxis.