Which statement best defines an allergic reaction?

• A. Severe immune response to an allergen with airway compromise
• B. Mild immune response to an allergen with hives or local swelling/itching
• C. Autoimmune reaction to an allergen
• D. Delayed hypersensitivity causing systemic reaction

Answer: (B)

Allergic reactions are immune responses to an external substance (an allergen) that are usually IgE-mediated and involve histamine release, producing symptoms that can range from mild to life-threatening. The statement describing a mild immune response with hives, local swelling, and itching captures the common, early presentation of an allergic reaction, making it the best fit for a general definition.

A severe immune response with airway compromise represents a more serious end of the spectrum—anaphylaxis—rather than the basic definition of an allergic reaction. An autoimmune reaction involves the immune system attacking the body's own tissues, which is not how allergies are defined. Delayed hypersensitivity refers to cell-mediated, often slower reactions (like contact dermatitis), not the immediate IgE-mediated responses typical of allergic reactions.