International Rhinologic Society Rhinology 0300-0729 2026 08 11 Impact of air quality on tissue eosinophilia and clinical severity of chronic rhinosinusitis EN A.Q. LeDepartment of Otolaryngology, Faculty of Medicine, Chulalongkorn University, Bangkok, Thailand Endoscopic Nasal and Sinus Excellent Center, King Chulalongkorn Memorial Hospital, Bangkok, Thailand Graduate Program in Clinical Sciences, Faculty of Medicine, Chulalongkorn University, Bangkok, Thailand Department of Otolaryngology, Faculty of Medicine, Pham Ngoc Thach University of Medicine, Ho Chi Minh City, Vietnam T. TranDepartment of Otolaryngology, Faculty of Medicine, Chulalongkorn University, Bangkok, Thailand Endoscopic Nasal and Sinus Excellent Center, King Chulalongkorn Memorial Hospital, Bangkok, Thailand Graduate Program in Clinical Sciences, Faculty of Medicine, Chulalongkorn University, Bangkok, Thailand Department of Otolaryngology, Hue Central Hospital, Hue City, Vietnam J. SamuthpongtornDepartment of Otolaryngology, Faculty of Medicine, Chulalongkorn University, Bangkok, Thailand Endoscopic Nasal and Sinus Excellent Center, King Chulalongkorn Memorial Hospital, Bangkok, Thailand Graduate Program in Clinical Sciences, Faculty of Medicine, Chulalongkorn University, Bangkok, Thailand K. SeresirikachornDepartment of Otolaryngology, Faculty of Medicine, Chulalongkorn University, Bangkok, Thailand Endoscopic Nasal and Sinus Excellent Center, King Chulalongkorn Memorial Hospital, Bangkok, Thailand W. ChitsuthipakornCenter of Excellence in Otolaryngology, Head-Neck Surgery. Rajavithi Hospital, Bangkok, Thailand College of Medicine, Rangsit University, Bangkok, Thailand M.P. Hoang Department of Otolaryngology, University of Medicine and Pharmacy, Hue University, Vietnam L.V. TranDepartment of Otolaryngology, Faculty of Medicine, Pham Ngoc Thach University of Medicine, Ho Chi Minh City, Vietnam Ear Nose and Throat Hospital, Ho Chi Minh City, Vietnam M.T.Q. LeDepartment of Otolaryngology, Faculty of Medicine, Pham Ngoc Thach University of Medicine, Ho Chi Minh City, Vietnam Ear Nose and Throat Hospital, Ho Chi Minh City, Vietnam S. ChusakulDepartment of Otolaryngology, Faculty of Medicine, Chulalongkorn University, Bangkok, Thailand Endoscopic Nasal and Sinus Excellent Center, King Chulalongkorn Memorial Hospital, Bangkok, Thailand J. KanchanaumpornDepartment of Otolaryngology, Faculty of Medicine, Chulalongkorn University, Bangkok, Thailand Endoscopic Nasal and Sinus Excellent Center, King Chulalongkorn Memorial Hospital, Bangkok, Thailand P. WungcharoenDepartment of Otolaryngology, Faculty of Medicine, Chulalongkorn University, Bangkok, Thailand Endoscopic Nasal and Sinus Excellent Center, King Chulalongkorn Memorial Hospital, Bangkok, Thailand K. SnidvongsDepartment of Otolaryngology, Faculty of Medicine, Chulalongkorn University, Bangkok, Thailand Endoscopic Nasal and Sinus Excellent Center, King Chulalongkorn Memorial Hospital, Bangkok, Thailand Letter 3501 10.4193/Rhin26.324 Particulate matter 2.5 (PM2.5) exposure impairs nasal epithelial defenses, disrupts mucociliary clearance, increases oxidative stress, and exacerbates inflammatory pathways associated with chronic rhinosinusitis (CRS). While it impacts upper airway diseases, the relationship between PM2.5 exposure and eosinophilic CRS (ECRS) with tissue eosinophil >10 cells/ HPF remains unclear. A cross-sectional study was conducted in Thailand and Vietnam to investigate the impact of PM2.5 exposure on tissue eosinophilia and the severity of CRS.