AbstractBackgroundChronic spontaneous urticaria (CsU) is a frequent dermatological disease that might last for months or years with high impact on quality of life. Known causes are autoreactive phenomena, infections or intolerances, rarely IgE‐mediated allergies. One‐third of CsU patients benefit from a low‐pseudoallergen diet. Additionally, it is often discussed, that reducing histamine ingestion alone might improve clinical symptoms and quality of life in CsU patients despite the uncertain role of the histamine‐degrading enzyme diamine oxidase (DAO).ObjectiveAim of this study was to investigate the impact of low‐histamine diet on symptoms and quality of life in patients with CsU.MethodsPatients suffering from CsU accompanied by gastrointestinal symptoms were included in the study. They underwent low‐histamine diet for at least 3 weeks. During the whole study, urticaria activity score (UAS) was recorded daily in a patient′s diary. Quality of life was assessed during screening, baseline and post diet visits by completing questionnaires (DLQI and Cu‐Q(2)oL). DAO activity was measured before and after elimination diet.ResultsA total of 75% of the patients had a benefit from the low‐histamine diet. Thirty‐four of 56 patients (61%) reached the primary endpoint of the study, an improvement of UAS 4 of ≥3. Overall, a significant reduction from 9.05 to 4.23 points (P = 0.004) was achieved; the average reduction in a strongly affected subgroup was 8.59 points (P < 0.001). DAO activity remained stable.ConclusionLow‐histamine diet is a therapeutically useful, simple and cost‐free tool to decrease symptoms and increase quality of life in CsU patients with gastrointestinal involvement. Further research is needed to understand the role of diamine oxidase.