histamine

Histamine is a chemical involved in the body's immune response and regulation of physiological functions. It is stored in certain cells, like those in your immune system, and is released during allergic reactions or tissue injury. Once released, histamine causes blood vessels to expand and become more permeable, leading to symptoms like redness, swelling, and itchiness. It also helps regulate stomach acid production and acts as a neurotransmitter in the brain, affecting alertness and mood. Medications like antihistamines work by blocking histamine's effects to relieve allergy symptoms or reduce stomach acid.