Histamine intolerance (HIT), like all so‑called biogenic amines intolerance syndromes, is still a mysterious problem of modern allergology. Its pathomechanism involves the imbalance between the amount of histamine consumed with food and degradation ability of intestinal enzymatic barrier. The main reasons are congenital and acquired deficiencies of the enteral diaminooxidase (DAO) activity, which is one of the histamine degrading enzymes. This results in appearance of symptoms after intake of aliments consisting histamine concentration harmless for the general population. HIT should be distinguished from histamine intoxication, when people with a fully functional enzymatic barrier experience symptoms after ingestion of food containing extremely high level of the mediator. Complex symptomatology of HIT, which is a classic example of pseudoallergy, consists of numerous non‑specific symptoms. It often creates a serious diagnostic challenge for allergists. It seems that this syndrome is underdiagnosed and underestimated amid allergic diseases. Moreover, the treatment is not easy due to difficulties in assessing the content of histamine in individual products. The literature review is presented below to outline the problem and analyze controversial issues, and to recapitulate the current state of knowledge on HIT and other posthistamine reactions.