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Acute sinusitis can be caused by the following:
Most cases of acute sinusitis start with a common cold, which is caused by a virus. Colds can inflame your sinuses and cause symptoms of sinusitis. Both the cold and the sinus inflammation usually go away without treatment within two weeks. If the inflammation produced by the cold leads to infection caused by bacteria, then this infection becomes acute sinusitis.
The inflammation caused by the cold results in swelling of the mucous membranes of your sinuses, trapping air and mucus behind the narrowed sinus openings. When mucus stays inside your sinuses and is unable to drain into your nose, it can become the source of nutrients for bacteria, which can then multiply.
Most healthy people have bacteria, such as Streptococcus pneumoniae and Haemophilus influenzae, in their noses and throats. Usually, these bacteria cause no problems, but when you sniff or blow your nose when you have a cold, these actions create pressure changes that can send typically harmless bacteria into the sinuses. If your sinuses stop draining properly, the bacteria can begin to multiply in your sinuses, causing acute sinusitis.
People who have allergies or other chronic problems that affect the nose also are prone to episodes of acute sinusitis. Chronic nasal problems cause the mucous membranes to swell and the sinus passages to become blocked. The normally harmless bacteria in your nose and throat again lead to acute sinusitis.
In general, people who have reduced immune function, such as those with primary immune deficiency disease (a defect in the way the immune system responds to infection) or HIV infection, are more likely to suffer from sinusitis. People who have abnormal mucus secretion or mucus movement, such as those with cystic fibrosis (an inherited disease in which thick and sticky mucus clogs the lungs, causing breathing problems and making it easier for bacteria to grow), also are more likely to suffer from sinusitis.
Infections caused by fungi very rarely cause acute sinusitis because the human body has a natural resistance to fungi; however, in people whose immune systems are not functioning properly, fungi can cause acute sinusitis.
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In chronic sinusitis, the membranes of both the paranasal sinuses and the nose thicken because they are constantly inflamed. Most health experts now use the term “chronic rhinosinusitis” to describe this condition. They also recommend that the condition be distinguished as either rhinosinusitis with or rhinosinusitis without nasal polyps.
Nasal polyps are grape-like growths of the mucous membrane that protrude into the sinuses or nasal passages, making it even more difficult for the sinuses to drain and for air to pass through the nose. The causes of chronic rhinosinusitis are largely unknown, but there are some conditions that may put you at higher risk for developing it, including the following:
Chronic rhinosinusitis often occurs in people who have asthma, many of whom also have allergies. It is possible that constant exposure to airborne allergens (substances that causes an allergic reaction) from house dust mites, pets, mold, and cockroaches causes chronic inflammation of the lining of the nose and the sinuses. An allergic reaction to certain fungi causes some cases of chronic rhinosinusitis: this condition is called allergic fungal sinusitis. However, at least half of all people who have chronic rhinosinusitis do not have allergies.
Although most health experts believe that chronic rhinosinusitis is not an infectious disease like acute sinusitis, if you suffer from frequent episodes of acute sinusitis, you may be prone to developing chronic rhinosinusitis. Some experts believe that chronic rhinosinusitis is caused by an exaggerated immune response to fungi that normally are found in the sinuses or to the bacterium Staphylococcus aureus, which commonly lives inside the nose.
As with acute sinusitis, other causes of chronic rhinosinusitis may be an immune deficiency disorder or cystic fibrosis.
Some people are born with a physical structure inside the nose that makes mucus flow out of the sinuses difficult. Others may develop a structural problem after experiencing an injury to the nose. These people are at higher risk for developing chronic rhinosinusitis.
Last Updated January 11, 2011
Last Reviewed January 11, 2011