Histamine Intolerance: Why the DAO Enzyme Story Is Incomplete, and the Real Reason Your Low Histamine Diet Stopped Working — The Four Sources of Histamine in Your Body

A useful mental model of histamine intolerance begins with the recognition that your body has four distinct histamine sources, each with its own dynamics, regulation, and contribution to symptoms. Standard treatment plans focus on one or two of these. The chronic patient is typically being driven by the ones the plan is not addressing. Source One: Dietary Histamine This is the source the standard story emphasizes. Foods accumulate histamine through bacterial fermentation, aging, processing, and storage. Fish that has not been refrigerated promptly develops high histamine through bacterial decarboxylation of histidine. Aged cheeses, cured meats, fermented vegetables, alcoholic beverages, and leftovers are dietary histamine sources. When dietary histamine enters the gut, DAO at the brush border of the small intestinal epithelium breaks it down before it can be absorbed into systemic circulation in significant quantities. Dietary histamine is the most controllable source. It responds to diet modification. It is also frequently not the dominant source in chronic histamine intolerance patients, which is why strict dietary control often does not resolve symptoms. Source Two: Mast Cell Tissue Histamine Mast cells are immune cells distributed throughout connective tissue: skin, gut wall, blood vessel walls, lungs, fascia, and beyond. They contain granules loaded with histamine, tryptas