Reasoning GP · Algorithm · 1-page summary
Loss of smell (anosmia and hyposmia)
For: adults with reduced, absent or distorted smell in primary care. Not for: true loss or distortion of taste (use the Taste disorders pathway). Lifelong anosmia with absent or incomplete puberty → endocrinology (block 2).
Core rule: unilateral loss with nasal signs, or any loss with new neurological features, is a red flag. Do not refer for Parkinson's on anosmia alone; consider neuroimaging if loss is unexplained after 3 months (NG127).
0Stop — call 999 now — before any history
- Acute confusion, reduced consciousness, seizure, meningism or new focal neurological signs → 999 / ED
- Severe headache with visual disturbance or papilloedema; sinonasal symptoms with orbital signs, rapidly progressive facial swelling or intracranial features → 999 / ED
- Suspected carbon monoxide: several people in one place with headache, dizziness, nausea, confusion, weakness or collapse; faulty heating → remove from the source, 999 if symptomatic or significantly exposed. Loss of smell is not a specific feature.
1Triage — one side or both, and what comes with it
| Pattern | Likely route |
|---|---|
| Unilateral + nasal signs | Obstruction, bleeding, crusting, mass, facial swelling → Urgent ENT / head and neck |
| Any + neurology | Headache, visual field loss, personality change → Same-day assessment and neuroimaging |
| Bilateral, after URTI/COVID | Post-viral; no blockage → olfactory training (block 5) |
| Bilateral + blockage | Rhinitis, CRS, polyps → nasal steroid + saline |
| Lifelong | With absent or incomplete puberty → endocrinology |
2Screen — one row is enough
- Olfactory groove meningioma: anosmia + headache + visual field loss + personality change → Same-day assessment and neuroimaging.
- Sinonasal malignancy: persistent unilateral loss with obstruction, epistaxis, crusting, facial swelling; woodworker or nickel worker → Urgent ENT / head and neck (local pathway; no NG12 criterion).
- Weight loss, night sweats, lymphadenopathy → Urgent ENT; check for an NG12 route (e.g. unexplained neck lump).
- Destructive nasal disease, septal perforation, suspected cocaine vasculitis, CT mass or bone erosion → Urgent ENT
- Tremor, rigidity, bradykinesia, gait disturbance → neurology for the parkinsonian features (NG71).
- Lifelong anosmia + absent or incomplete puberty (Kallmann) → endocrinology. MRI alone does not confirm it.
3Assess — once blocks 0–2 are answered
☐ Onset, side, nasal symptoms, head injury, COVID, smoking, cocaine, medicines, occupation ☐ Anterior rhinoscopy (polyps, oedema, septum) ☐ Gross smell test, one nostril at a time; visual fields; neurological examination when indicated; neck nodes
Targeted bloods only: B12/folate, TSH, HbA1c, FBC/ferritin when features suggest them; zinc only if deficiency is plausible. Not in primary care: Sniffin' Sticks/UPSIT, smell testing to diagnose Parkinson's, routine MRI for every case, COVID serology.
4Classify — only if the screen is negative
- Conductive — CRS, polyps, allergic rhinitis, septal deviation; nasal blockage → treat; usually reversible.
- Post-viral / COVID — sudden bilateral loss after URTI, no blockage; many recover over weeks to months.
- Parosmia — distorted smell after viral loss; may improve, but is not a reliable marker of recovery.
- Toxic or drug — cocaine, intranasal zinc, chemotherapy, overused decongestants → stop the cause.
- Head injury or neurodegenerative — anosmia in Parkinson's or Alzheimer's is non-specific.
- Uncertain — say so; review at 3 months, and consider neuroimaging if still unexplained (NG127).
5Treat today — only these
- CRS / polyps: mometasone nasal spray once or twice daily, head forward, away from the septum, for ≥12 weeks + saline douching twice daily. Oral steroids only on ENT advice.
- Allergic rhinitis: intranasal steroid + non-sedating antihistamine (loratadine 10 mg daily) — doses: NICE/SPC, BNF, local formulary.
- Post-viral: olfactory training — 4 familiar odours, about 20 seconds each, twice daily, ≥12 weeks. No routine supplements, zinc, theophylline, PRP or prednisolone.
- Safety: smoke, CO and gas alarms; use-by dates; weight and mood check; Fifth Sense.
6Refer routinely
- CRS/polyps not responding to 12 weeks of nasal steroid + saline → ENT (surgery; dupilumab is specialist only).
- Parosmia that persists, causes weight loss or affects nutrition and quality of life → smell clinic or ENT; dietitian if intake is restricted.
- Unexplained loss >3 months → consider MRI brain or ENT/neurology per local pathway; do not routinely refer if imaging is normal.
7Never reassure by
- Calling unilateral loss with nasal bleeding or crusting “just sinusitis”.
- Blaming ageing or sinusitis for anosmia with headache or visual change.
- A normal-looking nose when neurological features are present.
- Parosmia as proof of recovery.
- Anosmia alone as a reason to diagnose or refer for Parkinson's.
- Missing CO when several people in one home are unwell.
8Safety-net — say it, then document it
999 “Call 999 for confusion, drowsiness, a fit, or if you think there is carbon monoxide; go to A&E today for a severe headache with changed vision, or any new weakness, numbness or speech problem.” Urgent: “Bleeding from one side of the nose with the loss of smell — contact us now for an urgent ENT referral.”
Same week: “Weight loss, smell loss lasting beyond 3 months or getting worse, or distorted smell stopping you eating — book to see us.” Fit working smoke and CO alarms; check use-by dates.
✓Safe to leave primary care only if — all five, documented
No block 0–2 row applies
Bilateral; nose and neurology examined and normal
Cause named (post-viral, conductive) or uncertainty stated
Review booked at 3 months (12 weeks if on nasal steroid)
Safety-net, home safety and nutrition advice given
Summary of the full Reasoning GP loss of smell algorithm, which holds the detail and evidence. Sources: NICE NG127, NG71, NG12 (updated April 2026), TA1134; ENT UK GIRFT; British Rhinological Society; BSACI; ESCMID. Clinical reference — follow local policies and check doses: NICE/SPC, BNF.