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Sinus conditions and sinus anatomy

The sinuses do an important job, making mucus to keep the inside of the nose moist and helping to protect against dust, allergens and pollutants.

However, when things go wrong with the sinuses, such as blockages or infections, the result can be very painful.

Sinus anatomy

The sinuses are a connected system of hollow cavities in the skull.


The largest sinus cavities are around an inch across; others are much smaller. The sinus cavities include:

  • The maxillary sinuses (the largest), in the cheekbones.
  • The frontal sinuses, in the low-centre of the forehead.
  • The ethmoid sinuses, between the eyes, at the nasal bridge.
  • The sphenoid sinuses, in bones behind the eyes and nasal cavity.

The sinuses are lined with soft, pink tissue called mucosa. Normally, the sinuses are empty except for a thin layer of mucus.

The inside of the nose has ridges called turbinates. Normally these structures help humidify and filter air. The nose is divided in the centre by a thin wall, called the septum. Most of the sinuses drain into the nose through a small channel or drainage pathway called the middle meatus.

The purpose of the sinuses is unclear. One theory is that sinuses help humidify the air we breathe in; another is that they enhance our voices.

Sinus conditions

Acute sinusitis ( sinus infection): Viruses or bacteria infect the sinus cavity, causing inflammation. Increased mucus production, nasal congestion, discomfort in the cheeks, forehead or around the eyes and headaches are common symptoms. It often develops quickly and can go on for up to 12 weeks.

Chronic sinusitis (or chronic rhinosinusitis): More than just a series of infections, chronic sinusitis is a persistent process of inflammation of the sinuses that goes on for more than 12 weeks and can continue for several months.

Allergic rhinitis: Allergens like pollen, dust mites or pet dander cause the defences in the nose and sinuses to overreact. Mucus, nasal stuffiness, sneezing and itching result.

Deviated septum: If the septum that divides the nose deviates too far to one side, airflow can be obstructed.

Turbinate hypertophy: The ridges on the nasal septum are enlarged, potentially obstructing airflow.

Nasal polyps: Small growths called polyps sometimes grow in the nasal cavity, in response to inflammation. Asthma, chronic sinus infections and allergic rhinitis can lead to nasal polyps.

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