Anaphylaxis is best defined as

• A. A mild skin reaction to allergens.
• B. A life-threatening hypersensitivity reaction.
• C. A bacterial infection causing fever.
• D. A chronic autoimmune disease.

Answer: (B)

Anaphylaxis is a life-threatening hypersensitivity reaction that occurs rapidly after exposure to an allergen and involves systemic mediator release from mast cells and basophils. This surge causes widespread effects such as dramatic vasodilation and increased vascular permeability leading to a potential drop in blood pressure, along with bronchoconstriction and airway edema that can compromise breathing. Because it often involves multiple organ systems at once—typically skin changes plus respiratory or cardiovascular symptoms—it constitutes a medical emergency requiring immediate treatment with epinephrine and urgent care. This stands in contrast to milder allergic reactions that affect only the skin, infections with fever, or chronic autoimmune diseases, which do not present with the same rapid, systemic danger.