Histamine is produced as part of the local immune response to invading bodies and triggers inflammation, vasodilation, and increased capillary permeability. The increased permeability of the capillaries causes fluid to move into the extracellular space, giving rise to the classic symptoms of allergy such as a runny nose and watery eyes.

Further, sensory neural stimulation associated with the histamine release leads to sneezing, and nasal congestion occurs due to the vascular engorgement caused by increased vasodilation.

These are the classic symptoms of seasonal allergies, and for many patients these symptoms are temporary and self-limiting. For some patients, however, histamine-mediated reactions may come chronically, continuously, and sometimes, seemingly for no reason.

What is Histamine Intolerance?

Histamine intolerance (also known as Histaminosis) is an intolerance to a normal level of histamine in the body. It is usually caused by a lack of diamine oxidase (DAO) in the gut.

DAO normally breaks histamine down, so when DAO is insufficient, histamine uptake within the body is increased and an “overload” of histamine may occur. Once in the body histamine can then affect any and all cells which have histamine receptors on them including those in the skin, heart, lungs, brain, and gastrointestinal tract.

In patients with DAO deficiency and histaminosis, therefore, allergic reactions may be more severe and/or not just a temporary seasonal affliction.