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Coronavirus disease 2019 (COVID-19) is an infectious disease caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Since the start of the pandemic, olfactory dysfunction (OD) has been reported as a common symptom of COVID-19. In some asymptomatic carriers, OD is often the first and even the only symptom. At the same time, persistent OD is also a long-term sequela seen after COVID-19 that can have a serious impact on the quality of life of patients. However, the pathogenesis of post-COVID-19 OD is still unclear, and there is no specific treatment for its patients. The aim of this paper was to review the research on OD caused by SARS-CoV-2 infection and to summarize the mechanism of action, the pathogenesis, and current treatments. [ABSTRACT FROM AUTHOR]

The olfactory nerve (ON) is the only cranial nerve exposed to the external environment. Hence, it is susceptible to damage from head trauma, viral infection, inflammatory stimulation, and chemical toxins, which can lead to olfactory dysfunction. However, compared with all other cranial nerves, the ON is unique due to its inherent ability to regenerate. This characteristic provides a theoretical basis for treatment of olfactory dysfunction. Olfactory training (OT) is one of the main treatments for olfactory dysfunction. It is easy to apply and has few side-effects, and has been shown to be efficacious for patients with olfactory dysfunction of various causes. To further understand the application value of ON regeneration and OT on olfactory dysfunction, we review the research progress on the mechanism of ON regeneration and OT. [ABSTRACT FROM AUTHOR]