The Diabetic Nose: A Narrative Review of Rhinologic Involvement in Diabetes (1973-2025).

Background: Although diabetes mellitus is traditionally viewed as a systemic metabolic disorder, growing evidence indicates that it also affects the upper airways through vascular, inflammatory, and neuro-sensory mechanisms. The sinonasal mucosa, highly vascularized and immunologically active, may represent an early target of diabetic microangiopathy and immune-metabolic imbalance. Objectives: Our objectives are to synthesize current evidence on the rhinologic manifestations of DM, with a focus on chronic rhinosinusitis, olfactory dysfunction, and other nasal disorders, and to identify the main pathophysiologic and clinical patterns linking diabetes to sinonasal disease. Results: Evidence suggests that DM, particularly type 2 DM, increases susceptibility to CRSwNP and modulates the sinonasal microbiome toward Gram-negative predominance. Surgical outcomes after endoscopic sinus surgery are generally comparable between diabetics and non-diabetics when perioperative care is optimized. Olfactory dysfunction occurs more frequently and severely in diabetic patients, likely reflecting the combined effects of chronic inflammation, vascular compromise, and insulin resistance. Additional manifestations include recurrent epistaxis, delayed mucociliary clearance, and chronic cough. Allergic rhinitis appears to not be increased, and maybe even inversely related, especially among users of DPP-4 inhibitors. Conclusions: Diabetes intersects with rhinologic health through immune-metabolic, vascular, and epithelial pathways that may shape susceptibility, disease phenotype, and neurosensory decline. Future research should focus on disentangling type-specific mechanisms, metabolic biomarkers, and longitudinal outcomes, with the aim of developing precision-based approaches to rhinologic assessment and management in diabetic patients.