Inclusion Criteria:  18 to 90 years with confirmed history of COVID-19 (positive nasopharyngeal swab for SARS-CoV-2) subjective olfactory dysfunction persisting ≥ 90 days after follow-up negative COVID-19 nasopharyngeal swab  Exclusion Criteria:  previous history of olfactory-gustatory disorders impaired cognitive function history of neurodegenerative disease medical therapy with possible effects on olfactory function presence of rhinological disorders (sinusitis, rhinosinusitis, sinonasal polyposis, atrophic rhinitis, allergy) history of chemo-radiotherapy of the head and neck region history of stroke or neurotrauma severe nasal blockage from stenosis of deformity severe psychiatric illness (e.g. schizophrenia, bipolar disorder, olfactory hallucination) previous sinonasal nasopharyngeal tumors.