BACKGROUND: Patients with irritable bowel syndrome (IBS) have an increased risk of developing both airway and allergic diseases. However, the relationship between allergic rhinitis (AR), one of the most common chronic upper airway inflammatory diseases, and IBS remains poorly understood. The aim of this study is to provide a better understanding of airway complications in patients with IBS and to evaluate the presence of potential airborne and dietary antigen cross-reactivity in concomitant IBS and AR. METHODS: A total of 287 participants, 54 healthy volunteers without gastrointestinal complaints and 232 patients with I fulfilling Rome IV criteria, were invited to complete self-administered questionnaires assessing the severity of upper airway symptoms and the prevalence of allergic rhinitis. RESULTS: Overall, patients with IBS had a threefold higher risk of questionnaire-based allergic rhinitis than control subjects (95% CI, 1.49-6.12). Furthermore, patients with IBS + AR showed reduced sleep quality, mood, and personal satisfaction associated with their upper airway complaints, compared to IBS patients without AR. Forty-seven (18/38) percent of IBS + AR patients reported IBS symptoms in response to ingestion of food items with molecular mimicry of the aeroallergen to which the patient is sensitized. CONCLUSION: Our study shows that patients with IBS have an increased frequency of concomitant allergic rhinitis, which contributes to a further reduction in quality of life. We also provide evidence of potential cross-reactive reactions between aeroallergens and dietary antigens in patients with concomitant IBS and AR.