What is histamine?

Histamine is a biogenic amine that plays a crucial role in the body's immune response, particularly during allergic reactions. When the body encounters an allergen, histamine is released from mast cells and basophils. Its release leads to various physiological effects, such as increased blood vessel permeability, which allows immune cells to access affected tissues, and the dilation of blood vessels, resulting in common allergic symptoms like swelling, redness, and itching.

While histamine does have some involvement in neurotransmission within the brain, its primary and most well-understood role is in mediating allergic responses and inflammatory reactions. It acts primarily as a mediator of hypersensitivity and is not classified solely as a neurotransmitter. Additionally, it is neither a protein found in blood nor an enzyme involved in digestion, as these functions belong to different biological substances. Thus, identifying histamine as a hormone-like chemical responsible for responses during allergic reactions accurately captures its primary function within the immune system.