Anosmia
Anosmia is the partial or complete loss of smell. Common causes include viral infections (including COVID-19), nasal polyps, head trauma, or neurodegenerative diseases. Sudden loss after head injury requires urgent assessment.
🚨 Seek urgent care if
Loss of smell with any of these:
- Recent head injury or blow to the head
- Sudden neurological symptoms: weakness, confusion, vision changes
- Loss of smell after brain surgery
- Signs of skull base fracture (CSF leak from nose)
- Accompanied by severe headache or seizure
📞 See a GP or ENT if
Make appointment for:
- Loss of smell after viral illness (cold, flu, COVID-19)
- Gradual loss over weeks/months
- Nasal congestion, blockage, or discharge
- Reduced sense of smell with age
- Associated with Parkinson’s or Alzheimer’s symptoms
Types & associated conditions
| Presentation | Possible cause |
|---|---|
| Sudden loss after upper respiratory infection | Post‑viral olfactory loss (common after COVID-19, flu) |
| Gradual loss with nasal congestion, blockage | Nasal polyps, chronic sinusitis, allergic rhinitis |
| Loss after head trauma (even mild) | Olfactory nerve damage (shearing injury) |
| Progressive loss with motor symptoms | Parkinson’s disease or Alzheimer’s disease |
| Inability to smell since birth | Congenital anosmia (e.g. Kallmann syndrome) |
Causes by category
Nasal polyps: benign growths blocking airflow to olfactory cleft.
Chronic rhinosinusitis: inflammation obstructing smell.
Allergic rhinitis: seasonal or perennial allergies.
Deviated septum: mechanical obstruction.
Post‑viral olfactory loss: damage to olfactory epithelium (COVID-19, influenza).
Head trauma: shearing of olfactory nerves at cribriform plate.
Neurodegenerative diseases: Parkinson’s, Alzheimer’s – early sign.
Brain tumours: olfactory groove meningioma, frontal lobe tumours.
Kallmann syndrome: congenital anosmia + hypogonadism.
Aging: presbyosmia – gradual decline with age.
Toxins / medications: cocaine, intranasal zinc, some chemotherapy.
Radiotherapy: to head/neck damaging olfactory pathways.
Diagnostic procedures
Nasal endoscopy
Visualises nasal passages, polyps, inflammation.
MRI brain
Assesses olfactory bulbs, tracts, and excludes tumours.
CT sinuses
Detailed view of sinus anatomy and obstruction.
University of Pennsylvania Smell Identification Test (UPSIT)
Standardised scratch‑and‑sniff test quantifies smell loss.
Sniffin’ Sticks test
European odour identification, discrimination, threshold test.
Olfactory event‑related potentials
Electrophysiological test (research/tertiary centres).
