Histamine is a vital messaging molecule involved in regulating many functions in our body like digestion, sleep, mood, sexual function and our brain. Histamine is found in the mucous membranes in the smooth muscle of the gastrointestinal (GI) tract, uterus, lungs, skin, brain; produced by cells in our body; and present in certain foods. There are four different kinds of receptors in the body and each respond uniquely.