Nasal physiology: airflow, the nasal cycle, mucociliary clearance and smell

Applied anatomy

The nose warms, moistens and cleans the air, alternates which side is more open during the day, and holds the sense of smell high in its roof.

Updated Nov 5, 2026

Key points

The nasal cycle (alternating congestion of the turbinates, about every two and a half hours on average) is normal and found in most people; total resistance stays about the same.
Mucociliary clearance: ciliated epithelium with goblet cells moves mucus towards the throat; cold air slows the cilia (runny nose in the cold).
Primary ciliary dyskinesia: chronic rhinosinusitis, otitis media with effusion, neonatal respiratory distress and bronchiectasis; about half have situs inversus (Kartagener syndrome).
Olfactory neurons sit in the roof of the nose and send axons through the cribriform plate to the olfactory bulb; they are replaced throughout life.
Loss of smell: common after colds and sinus disease; also with polyps, head injury, ageing, and as an early sign of Parkinson or Alzheimer disease.

What it is

The nose is the air-conditioning unit of the airway. Turbinates make the air turbulent so it touches the mucosa and is warmed, moistened and filtered; a mucus blanket moved by cilia carries trapped particles to the throat; and a normal nasal cycle shifts congestion from side to side over hours. High in the roof, the olfactory epithelium detects odours, and smell provides most of what we call flavour. Knowing what is normal prevents unnecessary treatment and points to disease when a function fails.

Applied anatomy

Respiratory region: pseudostratified ciliated columnar epithelium with goblet cells over a rich vascular bed in the turbinates.
Olfactory region: specialised epithelium in the superior nasal cavity under the cribriform plate.
Turbinates (conchae) and meatuses on the lateral wall; the septum in the midline.
Retronasal route: odours released while chewing reach the olfactory epithelium from the throat.

Clinical physiology

Conditioning: turbinates enlarge the surface and create turbulence; meatuses recover moisture on exhalation.
Defence: mucus traps particles and microbes; cilia carry it to the pharynx to be swallowed.
Smell: odorant molecules dissolve in mucus and bind receptors on olfactory neurons, which signal the olfactory bulb.
Flavour: most of the 'taste' of food is smell; a blocked nose dulls food.

Clinical correlation

Patients often notice the nasal cycle only when one side is already narrowed, for example by a deviated septum.
Overuse of topical decongestant sprays causes rebound congestion; keep them to a few days.
Children with chronic wet cough, persistent rhinitis from birth and recurrent ear effusions should make you think of ciliary dyskinesia or cystic fibrosis.
Loss of smell is a safety risk (gas leaks, smoke, spoiled food) and affects nutrition and mood.
Head injury can shear olfactory axons at the cribriform plate.

Next step / Initial management

History: onset (after a cold, after a blow to the head, gradual), one or both sides, drugs, smoking, neurological symptoms; examine the nose for polyps.
Inflammatory causes: saline irrigation and intranasal corticosteroids; stop rebound decongestant use.
Post-viral smell loss: olfactory training and advice on gas and smoke detectors and food safety; many recover over time.
Refer routinely to ENT for smell loss lasting several months, smell loss with one-sided blockage, polyps or bloody discharge, or suspected ciliary dyskinesia.
Refer to neurology (routine, or urgent if other signs) when smell loss comes with neurological symptoms or after head injury.

Test yourself

Think of the answer, then tap the question to see it.

A healthy patient says one nostril blocks and then the other over the day. What is this and does it need treatment?

The nasal cycle: normal alternating congestion of the turbinates controlled by the autonomic system. It needs no treatment; total airflow stays about the same.

A child has chronic rhinosinusitis, ear effusions, bronchiectasis and dextrocardia. What is the diagnosis?

Primary ciliary dyskinesia with situs inversus (Kartagener syndrome): defective cilia fail to clear mucus in the nose, sinuses, middle ear and lungs.

Why do patients with a blocked nose complain that food has no taste?

Most flavour comes from smell: odours released in the mouth reach the olfactory epithelium through the back of the nose. Blocked airflow stops them.

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Educational content; it does not replace a medical assessment and is not a clinical instruction. For a real case, follow current guidelines and specialist advice.

Sources: Anatomy, Head and Neck, Nose (StatPearls (NCBI Bookshelf), 2023); Physiology, Olfactory (StatPearls (NCBI Bookshelf), 2023); Smell Disorders (National Institute on Deafness and Other Communication Disorders (NIDCD), NIH, 2023); Taste Disorders (National Institute on Deafness and Other Communication Disorders (NIDCD), NIH, 2023).

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Representative model, for educational purposes only.