Chemical released in allergic reaction

• A. Epinephrine
• B. Histamine
• C. Leukotrienes
• D. Sepsis

Answer: (B)

When an allergic reaction happens, mast cells release histamine in response to allergen exposure. Histamine acts quickly to widen blood vessels and increase their permeability, which leads to redness, swelling, and warmth. It also stimulates nerve endings, causing itch, and can cause bronchoconstriction, contributing to breathing difficulties. This rapid release explains many of the classic immediate symptoms of allergies.

Leukotrienes are produced as well and contribute to ongoing inflammation and later-stage bronchoconstriction, but they’re not the first or primary mediator released. Epinephrine isn’t released by immune cells during the reaction; it’s a hormone that the body may release in severe reactions or is given as a treatment to counteract allergy symptoms by relaxing airway smooth muscle and stabilizing blood pressure. Sepsis is unrelated to an allergic response, as it involves infection-driven systemic inflammation rather than allergen-triggered mast cell degranulation.

So the chemical most characteristically released in an allergic reaction is histamine.