Which statement correctly describes allergic reaction development?

• A. Develops after repeated exposure to the antigen over time
• B. Occurs immediately upon first exposure
• C. Is unrelated to histamine
• D. Always results in severe symptoms

Answer: (A)

Allergic reactions involve sensitization first. The immune system has to encounter the allergen and produce IgE antibodies that bind to mast cells and basophils. On a later exposure, the allergen cross-links those IgE molecules, causing degranulation and release of histamine and other mediators. This release leads to the symptoms of an allergy, which can range from mild to severe. Because sensitization takes time and usually requires repeated exposure, the reaction is not typically immediate on the first encounter. Histamine plays a central role in driving much of the symptoms, so responses that don’t involve histamine aren’t accurate. Reactions vary in intensity, so they aren’t always severe. That two-step process—sensitization with repeated exposure, followed by mediator release on re-exposure—best describes how allergic reactions develop.