The sinuses are hollow spaces in the bones behind the face. Directly behind the nose is a cavity. On either side of the nasal cavity are large sinuses. A row of very small sinuses runs behind the bridge of the nose, and two more large sinuses are located above and behind the inner part of the eyebrows.
Sinusitis is inflammation of the sinuses. It may be associated with both bacterial and viral infections, but it may be due to non-infectious inflammation (e.g., allergies) in the sinuses as well. Sinusitis can be acute and last less than 4 weeks, or chronic and last 8 to 12 weeks or more. Acute sinusitis is very common, affecting about 1 in 10 people each year.
People with diabetes or cystic fibrosis and people who are immunocompromised are at increased risk for sinusitis, as are those who were born with a malformed septum (the dividing wall between the nostrils).
The sinuses produce mucus that helps us clean the nose and to smell. It's moved out of the sinuses and into the nasal cavity by thousands of tiny hairs, called cilia, which operate in unison to form a sort of conveyor belt. Foreign particles and organisms entering the sinuses land in the mucus and are sent back to the nose. To get to the nose, the mucus has to pass through small holes in the bones that surround the sinuses.
Sinusitis usually begins during a bout of the common cold, influenza (flu), or some other viral infection. This causes the nasal mucous membrane (which is soft tissue inside the nose, not simply mucus) to swell. It can press against the hole through which mucus leaves a sinus.
Most cases of sinusitis are caused by viral infections. However, in a few people, a bacterial infection can develop. This is because when the sinus fills with mucus and empties of oxygen, it creates an ideal setting for bacteria to grow. The bacteria are often already in the nose, but don't cause an infection because they are held in check by the body's natural defences.
If the body's defences (e.g., the cilia, sinus drainage, or immune system) are not working properly, the bacteria can cause an infection. In rare cases, sinusitis can be caused by a fungal infection. People who get fungal sinus infections usually have other medical problems that affect their ability to fight infection (e.g., HIV, cystic fibrosis).
Other things that inflame the nose can also cause sinusitis. For example, hay fever and other allergies increase your chances of getting sinusitis.
Sinusitis has symptoms very different from a cold or the flu. The main symptoms are face pain or pressure, congestion, nasal discharge or post-nasal drip, and reduced ability to smell. The location of the pain depends on which sinus or sinuses are affected.
Infection of the lower (maxillary) sinuses causes toothache in the upper jaw and pain in the area under the eyes, while infection of the upper (frontal) sinuses causes pain in the temple. Infection of the small sinuses between the eyes (the ethmoid sinuses) causes pain between and behind the eyes.
Yellow or green pus may drain out of the nose, and there may be an unpleasant smell. Someone with sinusitis may feel generally unwell, but there shouldn't be a fever if the infection is confined to the sinuses.
Acute sinusitis usually lasts about 2 weeks. In a few people, however, the infection can last longer. When symptoms last more than 8 to 12 weeks, the condition is termed chronic sinusitis.
Serious complications of sinusitis can sometimes occur, including abscesses and meningitis (infection of the membranes surrounding the central nervous system).