Harmful chemicals in tobacco smoke cause cilia loss, mucus gland hypertrophy, inammation, and epithelial changes in the upper respiratory tract [32]. Consistent with the association between smoking and/or exposure to tobacco smoke at home and AR, tobacco exposure has also been shown to alter markers of allergic inam­mation such as total IgE, skin prick test positivity, and blood eosinophilia [33]. Also, there are different types of bacteria, viruses, and fungi in the respiratory tract of healthy people, just like in the gastrointestinal tract [34]. Microbial colonization of the respiratory tract can vary depending on exposures in the living environment (e.g., tobacco smoke), and bacterial dysbiosis can occur with prolonged exposure [35]. Tobacco smoke increases mucus production in the airways, impairs mucocili­ary clearance, and may affect the microbiota in the respiratory tract by disrupting favorable microenvironmental conditions by causing low-grade inammation [36]. Smoking is known to be a signicant risk factor for asthma and asthma attacks in children. In patients with AR and no asthma, the risk of developing asthma was found to be higher in the smoking group than in the non-smoking group (OR 2.98) [37]. Tobacco exposure is a risk factor for both asthma and AR, as well as for their co-occurrence [37].