Which term best describes the substance that triggers an allergic reaction?

Which term best describes the substance that triggers an allergic reaction?

• A. Antibody
• B. Allergen
• C. Mediator
• D. Antigen

Answer: (B)

Allergic reactions start when the immune system encounters a substance it mistakes for something harmful. The substance that triggers the reaction is called an allergen. An allergen is a specific type of antigen—the broader category of any substance that can provoke an immune response—but allergens are those that provoke an exaggerated response in susceptible people. Antibodies are the immune proteins made to recognize antigens, and mediators are the chemicals released during the reaction (like histamine) that cause the symptoms. So, the trigger itself in allergies is the allergen.

Allergic reactions start when the immune system encounters a substance it mistakes for something harmful. The substance that triggers the reaction is called an allergen. An allergen is a specific type of antigen—the broader category of any substance that can provoke an immune response—but allergens are those that provoke an exaggerated response in susceptible people. Antibodies are the immune proteins made to recognize antigens, and mediators are the chemicals released during the reaction (like histamine) that cause the symptoms. So, the trigger itself in allergies is the allergen.