Clinical and Immunological Perspectives on the Nasal Microbiome's Role in Olfactory Function and Dysfunction.

The nasal microbiome represents a complex and dynamic microbial ecosystem that contributes to mucosal defense, epithelial homeostasis, immune regulation, and olfactory function. Increasing evidence indicates that this microbial community actively interacts with host physiology, while alterations in its composition are associated with chronic inflammation, oxidative stress, and olfactory impairment. Such changes have been reported in conditions including chronic rhinosinusitis, allergic rhinitis, and post-viral anosmia. Beyond local effects, chronic nasal inflammation has been hypothesized to influence neuroinflammatory processes and protein aggregation pathways involving α-synuclein and tau, potentially linking nasal microbial imbalance to neurodegenerative mechanisms. However, current evidence remains largely indirect and does not support a causal relationship. This narrative review summarizes current clinical and immunological evidence on the role of the nasal microbiome in olfactory function and dysfunction, highlighting limitations of existing studies and outlining future research directions.