Which condition occurs when the immune system overreacts to a foreign substance, causing inflammation and organ dysfunction?

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

Answer: (B)

When the immune system overreacts to a harmless foreign substance, it triggers hypersensitivity reactions. In these responses, immune cells release mediators such as histamine and cytokines that cause inflammation, redness, swelling, and sometimes damage to organs. Allergic reactions are a common form of hypersensitivity, where exposure to things like pollen, pet dander, or certain foods leads to symptoms ranging from itching and runny nose to more severe responses. Hay fever is a specific example of this process, illustrating an allergic reaction. In contrast, immunodeficiency means the immune system is underactive, not overactive, and autoimmune hemolytic anemia involves the immune system attacking the body’s own red blood cells rather than reacting to a foreign substance.