Which term describes an exaggerated histamine and immune system response to a foreign substance?

• A. Hypersensitivity and allergic reactions
• B. Immunodeficiency diseases
• C. Pernicious anemia
• D. Hay fever

Answer: (A)

An exaggerated immune response to a harmless foreign substance is called hypersensitivity. In allergic reactions, exposure to an allergen triggers mast cells to release histamine, which causes symptoms like itching, swelling, runny nose, and sometimes bronchoconstriction. This broad category—hypersensitivity—describes the overreaction of the immune system to allergens. Immunodeficiency means the immune system is weakened, not overactive. Pernicious anemia is a vitamin B12 deficiency related issue, not about an overreactive immune response. Hay fever is a common example of an allergic reaction, but the term that covers the overall concept of an exaggerated immune response is hypersensitivity (allergic reactions).