Objective:Chronic rhinosinusitis (CRS) involves inflammation of the nasal and para-nasal mucosa.Due to its heterogeneous nature,unknown pathogenesis,and high recurrence rate,effective treatment is difficult.Nasal cytology is presently not a part of the routine diagnosis or treatment decision for CRS.Data sources:A literature search was performed for published papers in English between January 1990 and June 2019 using MEDLINE.Study sdection:Terms used were chronic rhinosinusids,eosinophils,etiology,immunopathology,inflammation,mast cells,nasal cytology,polyps,and treatment.Both reviews and original articles were collected and studied.Results:There is no standard nasal fluid,mucus sampling,or staining techniques for identifying inflammatory cell types.Results were divergent from different countries.Moreover,the main focus of these papers on the cells in nasal washings was eosinophils,with infrequent mentioning of other cell types that may imply different etiology and pathology.The heterogeneous cell profile of CRS and the role of mast cells have been unappreciated due to the lack of specific immunohistochemical technique or study of its unique mediators.Conclusions:Nasal cytology could help distinguish the type and the activation state of inflammatory cells.Thus it can help in providing a clearer picture of CRS pathogenesis,identifying different patient groups,and developing effective treatments.