The sinuses are air-filled spaces behind the bones of your face that open up into the nose cavity. They are lined with the same membrane as your nose. This is called the mucous membrane and it produces a slimy secretion called mucus to keep the nasal passageways moist and to trap dirt particles and bacteria.

You have four main sets of sinuses.

• The maxillary sinuses are in each cheekbone.
• The frontal sinuses are on either side of your forehead, above your eyes.
• The smaller ethmoid sinuses are behind the bridge of your nose, between your eyes.
• The sphenoid sinuses are between the upper part of your nose and behind your eyes.

The maxillary sinuses are the largest of the sinuses and the ones most commonly affected by sinusitis.

Sinus infection, or sinusitis, is an inflammation of one or more of your sinuses and nasal passages. A sinus infection can cause a headache or pressure in the eyes, nose, cheek area, or on one side of the head. A person with a sinus infection may also have a cough, a fever, bad breath, and nasal congestion with thick nasal secretions. Sinusitis is categorized as acute (sudden onset) or chronic (long term, the most common type).

If your sinusitis lasts anything from a few days up to a month it's called acute sinusitis. If your sinusitis is an ongoing problem lasting three months or more you may have chronic sinusitis (see Related topics). The medical terms acute and chronic refer to how long the condition lasts for, rather than how severe it is.
Acute sinusitis is common and can affect people of any age.

If you have sinusitis you may feel generally unwell and have a blocked nose. Sometimes people think they have a common cold when they have sinusitis. If you have sinusitis, your symptoms may include:

•    pain and pressure in your face, which is worse when you lean forwards
•    a blocked nose with green or yellow mucus, which can drain down the back of your nose into your throat and may cause a sore throat and cough
•    a headache when you wake in the morning
•    a fever
•    earache
•    toothache or pain in your upper jaw
On very rare occasions, a sinus infection can spread to the bones of the face or the membranes lining the brain.

Acute sinusitis is caused by an infection of the mucous membranes with a virus, bacterium or fungus. Most people with sinusitis have a viral infection such as the common cold.The mucus that is produced by the mucous membranes in your sinuses normally drains into your nose through small holes called ostia. The ostia can become narrow or even blocked if the sinuses get infected and inflamed so the mucus cannot drain properly.
This can also happen if your membranes are irritated by something. Examples of irritants include:

• airborne allergens such as grass and tree pollen
• smoke and air pollution
• sprays containing chemicals (eg household detergents)
• nasal decongestants, if overused
• chronic drug misuse (snorting substances such as cocaine)

Your GP will ask you about your symptoms and will examine you. He or she may also ask you about your previous illnesses and operations.

Your GP will usually be able to diagnose your sinusitis just from examining you and no further medical tests are usually necessary.

Due to the proximity of the brain to the sinuses, the most dangerous complication of sinusitis, particularly frontal and sphenoid sinusitis, is the spread of infection through the bones or by blood vessels by anaerobic bacteria to the brain. Abscesses, meningitis, and other life-threatening conditions may result. In extreme cases the patient may experience mild personality changes, headache, altered consciousness, visual problems, and, finally, seizures, coma, and possibly death.

Most people with acute sinusitis get better without treatment. However, you may find that home treatments and over-the-counter medicines provide some relief.

Some people find that breathing in steam from a bowl of hot (but not boiling) water containing a few drops of menthol oil (eg Olbas oil or Karvol) provides some relief from the symptoms. You can take the painkiller you usually take for a headache to relieve pain and lower your temperature if you have a fever.

Decongestant tablets, such as pseudoephedrine (eg Sudafed), may reduce swelling in your nose and allow your sinuses to drain. Decongestant nasal sprays are also available but you should not use them for more than a week, as prolonged use can actually make nasal blockage worse in the long run.

If your symptoms continue for more than a week you may wish to see your GP. If the sinusitis is thought to have been caused by a bacterial infection, your GP may prescribe antibiotics.

There are a number of things you can do to help prevent sinusitis developing such as:

• taking a short course (usually no longer than seven days) of decongestant medicine when you have a cold

• having a flu vaccination each year

• staying well hydrated by drinking plenty of fluids

• avoid smoking

• staying away from smoky environments

• keeping your allergy symptoms under control - ask your doctor or pharmacist for advice maintaining good general health by eating healthily and taking regular exercise