Histamine tolerance threshold
The amount of histamine the body can still break down without issues. It is not fixed and changes from day to day depending on health, medications, hormones, and stress.
Histamine intolerance can be pictured as a bucket. Histamine flows into it from food, from one's own mast cells, and from the activity of gut bacteria. It drains out thanks to the enzymes DAO and HNMT. As long as the outflow keeps up with the inflow, a person feels nothing. As soon as the level overflows the rim, symptoms arrive. That rim is the tolerance threshold. Scientific literature describes histamine intolerance in precisely this way - as an imbalance between accumulated histamine and the body's capacity to break it down.
Crucially, this threshold is not a fixed number. It is lowered by inflammation or a damaged intestinal mucosa, DAO-blocking medications, alcohol, a lack of DAO cofactors, acute infections, insufficient sleep, and stress. In women, it also fluctuates during the menstrual cycle, as estrogen and histamine mutually influence each other. Conversely, after an extended period of a stable routine and a healed gut, the threshold usually rises.
This explains a phenomenon that confuses people with HIT the most: the exact same portion of the exact same food is completely fine one day, yet causes symptoms the next. It is neither an error in measurement nor a mind game—the height of the threshold simply shifted in the meantime.
Related terms
Substances that release histamine from cells, worsening the symptoms of HIT.
An independent non-profit organization (Schweizerische Interessengemeinschaft Histamin-Intoleranz) that specializes in research, education and support for people suffering from histamine intolerance (HIT) and related disorders of mast cell metabolism.
The inability of the body to properly break down histamine, which leads to its excessive accumulation and manifestations.
Medications that prevent histamine from binding to receptors. However, they do not break histamine down; they only blunt its effect. In this way, they differ from DAO supplementation.
Immune system cells that release histamine and other mediators in response to HIT triggers.