Quick answer. A loss of smell is most often caused by a viral infection (including post-COVID) or nasal congestion from sinusitis and polyps, and usually settles on its own. The biggest red flag is a sudden loss of smell after a head injury or one alongside one-sided nasal symptoms or bleeding, which needs prompt review.
Smell can fade so gradually that you only notice when food tastes flat, or it can vanish overnight after a cold. In Singapore, the most common reason for a loss of smell is a simple viral infection or a blocked, congested nose from allergic rhinitis and sinus problems, and most people recover fully. Because smell and taste are closely linked, many people describe it as losing their sense of taste as well.
This guide explains the usual causes, how a gradual loss differs from a sudden one, and the warning signs that mean you should see a doctor rather than wait it out. It is a triage guide to help you decide what to do next, not a substitute for an in-person assessment.
At a glance
| Pattern | Likely cause | What usually helps |
|---|---|---|
| Sudden loss after a cold or flu | Viral infection (including post-COVID) | Often recovers over weeks to months; smell training can help |
| Blocked, congested nose with the loss | Sinusitis, nasal polyps, allergic rhinitis | Treating the congestion often restores smell |
| Gradual, painless decline over years | Ageing, long-standing nasal disease | ENT review to check for treatable causes |
| Loss right after a head injury | Damage to the smell nerves | Urgent medical review |
| One-sided loss with bleeding or blockage | Needs a tumour excluded | See an ENT specialist promptly |
Red flags: when a loss of smell needs urgent care
Most smell loss is not an emergency, but some patterns need prompt attention. Seek urgent or same-day care if your loss of smell comes with any of the following:
- It started right after a head injury – especially a significant blow, or if you also have clear watery fluid dripping from the nose, persistent headache, confusion or drowsiness. Call 995 or go to A&E for a head injury with these features.
- One-sided nasal symptoms – a blockage, discharge or repeated bleeding from only one side of the nose, particularly in adults, should be checked to exclude a growth or tumour.
- Sudden one-sided weakness, facial droop or slurred speech alongside the symptom – treat as a possible stroke and call 995 immediately.
A gradual, painless loss of smell without these features is not an emergency, but it still deserves a non-urgent appointment so a treatable cause is not missed.
Viral infections, including post-COVID
A viral upper respiratory infection is the single most common cause. The viruses that cause colds, flu and COVID-19 can inflame or temporarily damage the smell receptors high in the nose.
- During the infection – swelling blocks odours from reaching the receptors, so smell drops while the nose is congested.
- After the infection – some people have a lingering loss even once the nose clears, known as post-viral or post-COVID smell loss. It often improves slowly over weeks to months, and structured smell training (regularly sniffing familiar scents) may help recovery.
Nasal congestion, sinusitis and polyps
Anything that physically blocks airflow or inflames the lining of the nose can dull smell. These causes are common in Singapore given high rates of allergic rhinitis from dust mites and the periodic haze.
- Allergic rhinitis – persistent congestion, sneezing and a runny nose that blunt smell, often worse with dust or haze exposure.
- Chronic sinusitis – long-standing inflammation of the sinuses, sometimes with facial pressure and thick discharge.
- Nasal polyps – soft swellings in the nasal lining that block airflow and are a recognised cause of reduced smell; they often respond well to treatment.
When the loss of smell tracks with how blocked your nose feels, treating the underlying congestion frequently restores it.
Head injury, ageing and rarer neurological causes
Beyond infection and congestion, other causes are worth knowing about:
- Head injury – a blow to the head can shear the delicate smell nerve fibres as they pass through the skull, causing a sudden loss. This always warrants medical review.
- Ageing – smell naturally declines with age, usually gradually and painlessly.
- Neurological conditions – rarely, a reduced sense of smell can be an early feature of conditions such as Parkinson’s disease or dementia, typically alongside other symptoms rather than on its own.
- Medications and exposures – certain drugs and chemical exposures can affect smell.
Gradual versus sudden loss of smell
How quickly your smell faded is a useful clue:
- Sudden loss – most often points to a viral infection or, if it followed a head injury, to nerve damage. A sudden one-sided loss should be assessed.
- Gradual loss – tends to suggest a slowly progressive cause such as long-standing nasal disease, polyps or ageing. Because it creeps up, it is often noticed late, so it is still worth checking even if it has been present for a while.
Note whether your sense of smell fluctuates with congestion, as that usually means a treatable nasal cause.
Which specialist should you see?
For a persistent loss of smell, the right doctor is usually an ENT (ear, nose and throat) specialist, who can examine the inside of the nose with a small scope and look for congestion, polyps, sinus disease or other treatable causes. You can see an ENT specialist in Singapore directly if the loss is one-sided, follows a head injury, or has not improved.
If your symptoms are mild, recent and clearly linked to a cold, it is reasonable to start with your GP, who can treat congestion and refer you onward if smell does not return. Do not wait, though, if the loss came on after a head injury, especially with clear nasal fluid, headache or drowsiness – call 995 or go to A&E. Likewise, treat sudden one-sided weakness, facial droop or slurred speech as a possible stroke and call 995 straight away.
Related guides
- Best ENT Clinics in Singapore — our editorial shortlist
- ENT clinics directory
- Ear discharge
- Watery eyes
- Itchy scalp
- Indigestion
Sources
- NHS – Lost or changed sense of smell
- Mayo Clinic – Anosmia (loss of smell)
- HealthHub Singapore
- NHS – Nasal polyps
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