Histamine is an endogenous, short-acting biogenic amine that is synthesized from the amino acid histidine and is widely found throughout the body. Histamine is stored in basophils' and mast cells' granules and is an important mediator of direct allergic reactions. Normally, there is a minimal amount of histamine in the bloodstream. Increased histamine levels in plasma and tissues occur during anaphylaxis and in allergic skin and airway reactions.
Histamine also belongs to a class of neurotransmitters called low molecular weight neurotransmitters. This group includes molecules such as serotonin, epinephrine, and dopamine.
In addition, histamine plays a role in the secretion of gastric acid in the stomach, by inducing its production.