Histamine is a biogenic amine, which occurs naturally in the human body. Histamine can be metabolised with Diamine Oxidase (DAO) Enzyme. It is estimated that in 1% of people, as a result of an imbalance between the supply and degradation of histamine, a condition called histamine intolerance (HIT) develops. The case report describes a 40-year-old women who visited the Emergency Room several times due to quickly increasing face oedema, rush, chest pain and dyspnoea after eating meals containing histamine. For many years, the patient has struggled with non-specific symptoms. The woman decided to have a test performed to determine the enzymatic activity of DAO in the blood serum. The result was 5 U/ml, which indicates a significant shortage of DAO. Taking into consideration the symptoms the patient presented, extensive differential diagnosis, which excluded the presence of other diseases and serum DAO activity test, it was possible to diagnose histamine intolerance caused by DAO deficiency