What is the difference between anosmia and hyposmia?

Anosmia is complete loss of smell; hyposmia is a reduced sense of smell. Both also dull the flavour of food because flavour is mostly smell.

What most commonly causes loss of smell?

Nasal and sinus problems — a blocked nose, chronic sinusitis, nasal polyps and allergic rhinitis — are the commonest, followed by viral infections including colds, flu and COVID-19.

Will smell come back after COVID-19?

Often yes, but not always. Post-viral smell loss frequently recovers, though nerves may take six months or longer, and some people have lasting loss or distorted smell. Smell training can help.

What is smell training?

Regularly sniffing a set of familiar scents (commonly rose, lemon, clove and eucalyptus), about twice a day for roughly 20 seconds each over several months, to help retrain the smell system; it is most useful for post-viral loss.

When should I see a doctor?

If smell loss is persistent, or if you have persistent one-sided nasal blockage, blood-stained nasal discharge, or neurological symptoms. In Singapore, one-sided nasal symptoms warrant checking because of nasopharyngeal cancer.

Loss of Smell (Anosmia): Causes, Smell Training & Red Flags (Singapore)

Written & reviewed by the BestDoctors.sg editorial team · Last updated 1 Sep 2026 · General information, not medical advice

Quick answer. Loss of smell means the sense of smell is reduced (hyposmia) or absent (anosmia); because smell drives most of what we experience as flavour, it also dulls taste. The commonest causes are nasal and sinus problems – a blocked nose, chronic rhinosinusitis, nasal polyps and allergic rhinitis – followed by viral infections such as colds, flu and COVID-19, where smell often but not always recovers. Losing smell matters for safety (detecting smoke, gas or spoiled food), appetite and mood. Persistent smell loss should be assessed – and in Singapore, persistent one-sided nasal symptoms or blood-stained discharge should always be checked.

Struggling with sinus, hearing, throat or balance problems?

Message our care team on WhatsApp. Tell us what’s going on and we’ll help you find the right ENT specialist — free, with no obligation.

Chat with our care team on WhatsApp

Not sure who to see? Find the right specialist →

In a medical emergency, or for severe or sudden symptoms such as breathing difficulty, chest pain, fainting or stroke signs, call 995 immediately.

Most smell loss comes from a blocked or inflamed nose, or follows a viral infection – but a few patterns, especially one-sided nasal symptoms, deserve a proper check rather than being waved off as a lingering cold.

What it is

Smell (olfaction) begins when odour molecules drawn into the nose reach a small patch of specialised nerve tissue high in the nasal cavity, which sends signals along the olfactory nerve to the brain. Anything that blocks odours from reaching this area, or that damages the nerve pathway itself, can dull or remove the sense of smell. The loss can be partial (hyposmia) or complete (anosmia), and it may affect all smells or only certain ones. A distorted sense of smell (parosmia – ordinary things smelling wrong or unpleasant) or phantom smells (phantosmia) can also occur, notably after a viral illness.

Because most of what we call “taste” is really smell, food often tastes bland or flat when smell is lost, even though the tongue’s basic tastes – sweet, salty, sour, bitter and savoury – usually remain intact. This is why many people first notice the problem at mealtimes rather than through smells themselves.

Common causes

Nasal and sinus problems are by far the commonest cause, because they physically obstruct odours or inflame the smell area. These include an ordinary blocked nose, chronic sinusitis, nasal polyps and allergic rhinitis – the last especially relevant in Singapore, where dust-mite and other allergies are widespread. Viral infections – the common cold, influenza and COVID-19 – are the next commonest, and can damage the smell nerves as well as swelling the nose.

Other common contributors include:

Head injury, which can shear or bruise the delicate olfactory nerve fibres.
Ageing, as the sense of smell gradually fades in later life.
Smoking, which irritates and blunts the smell tissue over time.
Certain medicines from several drug classes; if smell loss began after starting a new medication, mention it to your doctor rather than stopping the medicine yourself.

Less common but important causes

A minority of cases point to something that needs specialist attention. Nasal and sinus tumours, including nasopharyngeal (nose) cancer, can present with progressive, often one-sided nasal blockage or bleeding. Neurological conditions can also reduce smell: loss of smell may be an early feature of Parkinson’s disease, sometimes preceding movement symptoms by years, and reduced smell is recognised in some forms of dementia. These causes are uncommon, but they are the reason persistent or one-sided smell loss should be assessed rather than assumed to be a lingering cold.

COVID-19 and post-viral smell loss

Post-viral smell loss frequently improves as inflammation settles and nerve function recovers, but recovery is not guaranteed and damaged nerves may take six months or longer; some people are left with lasting loss or a distorted sense of smell (parosmia). Recovery tends to be gradual rather than sudden, and smell training (below) is often recommended during this period. If loss follows a clear viral illness and is slowly improving, watchful waiting is reasonable – but loss that is worsening, one-sided, or accompanied by the warning signs below still warrants review.

When smell loss is a warning sign

Most smell loss is benign, but certain features should prompt a prompt medical check rather than waiting:

Smell loss after a head injury.
One-sided nasal blockage, or blood-stained nasal discharge or nosebleeds on one side.
A neck lump, one-sided ear blockage or hearing change alongside nasal symptoms – a pattern that, in Singapore, should raise the question of nasopharyngeal cancer.
Smell loss with neurological symptoms – limb weakness, numbness, vision or speech changes, or a change in balance, thinking or movement.
Progressive loss with no cold, allergy or clear viral trigger.

Call 995 if smell loss comes with sudden stroke-like symptoms – face drooping, arm weakness, slurred or garbled speech, or sudden vision loss – as these need emergency care.

How it is assessed

A doctor – a GP or polyclinic doctor first, and often an ENT specialist – will start with your history: how the loss began, whether it was sudden or gradual, any recent viral illness, injury, allergies, medicines or one-sided symptoms. Examination of the nose follows, sometimes with a nasal endoscopy (nasoendoscope), a thin flexible camera that lets the specialist see the nasal passages, sinus openings and the back of the nose. Smell testing using standardised scent kits can measure how much smell has been lost and track recovery over time. Where a structural or neurological cause is suspected, imaging – a CT scan of the sinuses or an MRI of the nose and brain – may be arranged.

Complications and impact

Loss of smell is a genuine safety issue: people may fail to detect smoke from a fire, a gas leak, or food that has spoiled, all of which raise the risk of harm at home. Beyond safety, it reduces the enjoyment of food, which can dull appetite and, in some people, lead to unintended weight change or poorer nutrition. The loss of a whole sense – and of the memories and pleasures tied to smell – can also affect mood, and persistent smell loss is linked with low mood and reduced quality of life. These effects are real and worth raising with your doctor.

Treatment

Treatment is aimed at the underlying cause. For nasal inflammation, polyps or allergic rhinitis, steroid nasal sprays and saline (salt-water) rinses reduce swelling and can restore airflow to the smell area; treating sinus disease – medically, and occasionally with surgery for polyps or chronic sinusitis – may recover smell where blockage is the problem. For allergy, avoiding triggers and using regular treatment helps. Medicines are described here by class only; the right choice and dose are decisions for your doctor.

For post-viral loss, smell training may aid recovery: this involves regularly and deliberately sniffing a set of distinct scents – commonly rose, lemon, clove and eucalyptus – twice daily over several months, which is thought to help the smell pathway relearn. It is safe, inexpensive and worth trying. Importantly, some causes are not reversible – where the olfactory nerve has been permanently damaged by injury, ageing or long-standing loss, smell may not fully return, and treatment then focuses on safety and coping.

Living with it and safety tips

If smell is reduced or lost, a few practical steps protect you and keep food enjoyable:

Fit and maintain smoke alarms, and use a gas detector or switch to electric cooking if you rely on gas – you cannot rely on smelling danger.
Check food dates and store leftovers carefully; when in doubt, throw it out rather than relying on smell to judge freshness.
Take extra care with anything that gives off fumes at home.
Keep meals appealing through texture, temperature, colour and seasoning (herbs, chilli, sour and savoury notes) since basic tastes usually remain.
Tell family or housemates, so someone can help flag smells you might miss.

When to see a doctor

See a GP or polyclinic doctor for smell loss that is persistent, unexplained, or not improving after a viral illness. Seek review promptly for smell loss after a head injury, one-sided nasal blockage or bleeding, or smell loss with neurological symptoms such as weakness, numbness, or vision or speech changes; an ENT referral is appropriate for one-sided or blood-stained nasal symptoms, a neck lump, or one-sided ear blockage, given the local relevance of nasopharyngeal cancer. Reliable general information is available on HealthHub (MOH Singapore). Call 995 for sudden stroke-like symptoms – face drooping, arm weakness, slurred speech, or sudden vision or speech changes.

Related ear, nose & throat conditions

Sources

NUH — anosmia (loss of smell): definitions, causes, smell testing, olfactory retraining (Singapore patient education).
SGH — loss of smell can signal issues apart from COVID-19: viral causes, recovery timeline, smell training.
HealthHub (MOH Singapore) — nasopharyngeal cancer: one-sided nasal symptoms and blood-stained discharge as red flags.
Cleveland Clinic / ENT Health (AAO-HNS) — causes, the taste link, and smell-retraining method.

General information only. This guide is general information about an ear, nose or throat condition and is not a diagnosis or personalised medical advice. See a doctor — a GP or an ENT specialist — for assessment, tests and treatment. Sudden hearing loss in one ear should be seen urgently, and call 995 for sudden severe vertigo with a bad headache, slurred speech, double vision or one-sided weakness.

Loss of Smell (Anosmia) in Singapore