Box 2.

Causes of olfactory disturbance

Conductive	Sensorineural
Chronic rhinosinusitis	Viral/post-viral (including COVID-19)
Nasal polyps	Head trauma
Allergic rhinitis	Medication related (for example, ACE inhibitors, diuretics, calcium channel blockers, statins, tobacco. Alcohol and illicit drug (especially cocaine) abuse
Gross septal deviation	Neurological (temporal lobe epilepsy, multiple sclerosis, cerebrovascular disease)
Intranasal tumours	Neurodegenerative disease (for example, Parkinson’s and Alzheimer’s)
Granulomatous disease of the nose	Space-occupying lesion (that is, anterior cranial fossa tumours)
Iatrogenic (for example, nasal surgery and laryngectomy)	Congenital (for example, Kallmann’s)