Which term denotes an extreme hypersensitivity reaction to a previously encountered antigen?

• A. Anaphylaxis
• B. Allergy
• C. Systemic Effect
• D. Toxicity

Answer: (A)

Extreme hypersensitivity reaction to a previously encountered antigen is called anaphylaxis. It happens when the immune system overreacts to something it has seen before—such as certain foods, insect venom, or medications—and releases mediators like histamine all over the body. This leads to rapid, widespread symptoms such as swelling of the airways, trouble breathing, hives, dizziness or faintness, and low blood pressure, potentially progressing to shock. Because of its severity and speed, it’s the specific term that fits this description and it requires urgent treatment with epinephrine and medical care. By contrast, an allergy is a broader term for immune reactions to a substance (which can be mild or local), a systemic effect is not a precise medical term for this concept, and toxicity refers to damage from poisons, not an immune-mediated reaction to an antigen.