April/May 2026 Vol 25.2Histamine Intolerance Through a Functional Medicine Lens: A Systems-Based Review
Authors: Elena Colussi-Pelaez MD
Abstract:
Histamine intolerance (HIT) is an increasingly recognized clinical syndrome characterized by an imbalance between histamine accumulation and an individual’s capacity for degradation. Patients frequently present with gastrointestinal, dermatologic, neurologic, and systemic symptoms, including flushing, headaches, urticaria, and gastrointestinal distress. Despite growing awareness, HIT remains underdiagnosed, as standardized diagnostic criteria and evidence-based treatment pathways are yet to be established. Symptom overlap with migraine, chronic urticaria, and functional gastrointestinal disorders contributes to a substantial clinical burden. Diamine oxidase (DAO) and histamine-N-methyltransferase (HNMT) are the primary enzymes responsible for histamine metabolism, and reduced activity, whether due to genetic variants, intestinal mucosal injury, medication effects, or nutrient insufficiencies, may contribute to symptom expression.
