Histamine is a chemical produced by the body that plays a crucial role in the immune response. It is released during allergic reactions and helps to regulate physiological functions, such as gastric acid secretion and neurotransmission. When the body encounters an allergen, histamine causes blood vessels to expand and become more permeable, leading to symptoms like itching, swelling, and redness. In addition to its role in allergies, histamine is also involved in the central nervous system, where it acts as a neurotransmitter. It helps to regulate sleep-wake cycles and cognitive functions. Understanding histamine is important for managing allergies and other related health conditions.