Anosmia / Smell Loss

Terminology

Olfactory disorders include anosmia (complete loss of smell), hyposmia (reduced smell), parosmia (distorted smell perception), dysgeusia (distorted taste), and phantosmia (perceiving smells that aren’t present).

Causes

Sinonasal disorders (see Rhinitis, Sinusitis & Rhinosinusitis and Nasal Polyps — mechanical obstruction of the olfactory cleft); post-viral (upper respiratory tract infections accounted for ~40% of anosmia cases before COVID-19, typically resolving within 12 months; COVID-19 itself — ~47% of patients self-report an olfactory disorder, and sudden-onset anosmia may be the earliest COVID-19 symptom in ~25% of cases); traumatic (head injury, skull base fracture); congenital; neurodegenerative (an early feature of Parkinson’s disease); other infectious causes.

Impact

Often profoundly affects quality of life — loss of enjoyment of food (can contribute to malnutrition), safety concerns (inability to detect smoke, gas leaks, spoiled food), and psychosocial impact (difficulty with intimacy, social eating, and — for some occupations, e.g. chefs, sommeliers, nurses, firefighters — professional function). This distress warrants the same clinical consideration as loss of sight or hearing, even though it’s rarely an urgent presentation. Consider dietitian, psychology, and occupational rehabilitation referral where relevant.

Assessment

History: onset (sudden vs gradual), duration, associated nasal symptoms (congestion, discharge — suggests sinonasal cause), recent URTI/COVID-19, head trauma, medication review, and neurological symptoms. Examine the nose (polyps, mucosal disease) and consider a basic neurological assessment if no sinonasal cause is apparent (especially with other neurological features, raising possibility of a central cause).

Management

Post-viral/post-COVID-19 anosmia: up to 50% of patients with COVID-19-related anosmia have smell/taste alteration lasting ≥6 months. Evidence for pharmacological treatments (intranasal/systemic corticosteroids, omega-3, zinc sulfate, alpha-lipoic acid, theophylline, vitamin A, Ginkgo biloba, sodium citrate) is currently insufficient to recommend them — large RCTs are still needed.

Olfactory training (“smell training”) has growing evidence and international body support (British Rhinological Society), and is a safe, inexpensive, GP-initiable treatment — recommended for symptoms lasting more than 2 weeks. Protocol: the patient inhales a familiar scent for 30 seconds, pauses 30 seconds, then moves to the next scent, twice daily over several months. The standard four-scent kit (rose, eucalyptus, clove, lemon) has evidence for effectiveness in post-infectious olfactory disorders when started within 12 months of onset. Patient resources: Fifth Sense (fifthsense.org.uk) and AbScent (abscent.org) provide self-training kits and progress-logging tools.

Refer to otolaryngology for persisting symptoms, or where a sinonasal, traumatic, or other structural cause needs specific management.