Quote from Histamine and Histamine Intolerance:
"Histamine intolerance results from a disequilibrium of accumulated histamine and the capacity for histamine degradation. Histamine is a biogenic amine that occurs to various degrees in many foods. In healthy persons, dietary histamine can be rapidly detoxified by amine oxidases, whereas persons with low amine oxidase activity are at risk of histamine toxicity. Diamine oxidase (DAO) is the main enzyme for the metabolism of ingested histamine. It has been proposed that DAO, when functioning as a secretory protein, may be responsible for scavenging extracellular histamine after mediator release. Conversely, histamine N-methyltransferase, the other important enzyme inactivating histamine, is a cytosolic protein that can convert histamine only in the intracellular space of cells. An impaired histamine degradation based on reduced DAO activity and the resulting histamine excess may cause numerous symptoms mimicking an allergic reaction. The ingestion of histamine-rich food or of alcohol or drugs that release histamine or block DAO may provoke diarrhea, headache, rhinoconjunctival symptoms, asthma, hypotension, arrhythmia, urticaria, pruritus, flushing, and other conditions in patients with histamine intolerance. Symptoms can be reduced by a histamine-free diet or be eliminated by antihistamines."
If plasma histamine concentrations are very high, you will experience symptoms of histamine poisoning. But if plasma concentrations are less elevated, you may only observe elevated gastric acid secretion and elevated heart rate, - and therefore maybe not get a suspicion to histamine intolerance.
In videos from Dr. Janice Vickerstaff Joneja you can learn more about histamine intolerance.
Histamine is involved in the immune system and also act as a neurotransmitter. I found this interesting paper about histamine's impact on the immune system: Histamine Potently Suppresses Human IL-12 and Stimulates IL-10 Production via H2 Receptors
"IL-12 and IL-10, respectively, stimulate Th1 and Th2 immune responses. The development of some allergic reactions, infections,and tumors are associated with excessive histamine production and a shift toward Th2 responses"...."Thus, histamine, via stimulation of H2 receptors on peripheral monocytes and subsequent elevation of cAMP, suppresses IL-12 and stimulates IL-10 secretion, changes that may result in a shift of Th1/Th2 balance toward Th2-dominance. This may represent a novel mechanism by which excessive secretion of histamine potentiates Th2-mediated allergic reactions and contributes to the development of certain infections and tumors normally eliminated by Th1-dependent immune mechanisms."For Danish readers - Til danske læsere:
Region Midtjylland har udgivet en pjece om histamin intolerance: Madens mulige betydning ved histamin intolerance