Toward a Cytological Classification of Nasal Biofilms in Upper Airway Inflammation: Microscopic Patterns, Clinical Meaning, and Therapeutic Implications

Background/Objectives: Nasal biofilms are increasingly recognized as contributors to chronic and recurrent upper airway inflammation, yet their cytological interpretation is still often reduced to a binary presence/absence judgment, underestimating their morphological, microbial, and inflammatory heterogeneity. This Perspective proposes a cytological classification framework for nasal biofilms based on microscopic morphology, degree of organization, bacterial and fungal composition, host inflammatory response, and therapeutic implications. Methods: This conceptual framework integrates standardized nasal cytology, microscopic observation of bacterial aggregates and biofilm-like structures, May–Grünwald–Giemsa staining features, and current knowledge of biofilm behavior in upper airway inflammatory disorders, focusing on relationships among bacteria, fungal elements, mucus, epithelial cells, and inflammatory infiltrates. Results: Five cytological patterns are proposed: free bacterial colonization, microaggregate biofilm-like pattern, structured/mature biofilm pattern, inflammatory biofilm-associated pattern, and dispersal/disrupted biofilm pattern, reflecting different degrees of microbial organization and host–microbe interaction and possibly coexisting within the same smear. Nasal cytology may also reveal fungal-predominant or mixed bacterial–fungal patterns, supporting an “infectious condominium” concept, and should distinguish isolated fungal spores from the rarer, clinically more significant vegetative forms such as hyphae. Conclusions: Moving from a presence/absence approach to pattern-based interpretation may improve the diagnostic and clinical value of nasal cytology. Although prospective validation is required, this classification offers a shared descriptive language that may support more precise phenotyping of upper airway inflammation, avoid overinterpretation of simple colonization, and inform personalized diagnostic and therapeutic strategies.