Cause
Acute Sinusitis
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 2 weeks. If the inflammation produced by the cold leads to a bacterial infection, however, then this infection is what health experts call acute sinusitis.
The inflammation caused by the cold results in swelling of the mucous membranes (linings) of your sinuses, and this can lead to air and mucus becoming trapped behind the narrowed openings of the sinuses. When mucus stays inside your sinuses and is unable to drain into your nose, it can become the source of nutrients (material that gives nourishment) for bacteria.
Most healthy people harbor bacteria, such as Streptococcus pneumoniae and Haemophilus influenzae, in the nose and throat, and the bacteria cause no problems. But when you have a cold, you tend to sniff or to blow your nose, and these actions cause pressure changes that can send bacteria inside the sinuses. If your sinuses then stop draining properly, bacteria that may have been living harmlessly in your nose or throat can begin to multiply in your sinuses, causing acute sinusitis.
People who suffer from allergies that affect the nose (like pollen allergy, also called hay fever), as well as people who may have chronic nasal symptoms not caused by allergy, are also prone to develop episodes of acute sinusitis. The chronic nasal problems cause the nasal membranes to swell, and the sinus passages become blocked in a manner similar to that described above for the common cold. The normally harmless bacteria in the nose and throat again lead to acute sinusitis.
Rarely, fungal infections can cause acute sinusitis. Although fungi are abundant in the environment, they usually are harmless to healthy people because the human body has a natural resistance to fungus. However, in people whose immune system is not functioning properly, fungus, such as Aspergillus, can cause acute sinusitis. (Aspergillus is commonly found growing on dead leaves, stored grain, compost piles, or in other decaying vegetation.)
In general, people who have reduced immune function (such as those with primary immune deficiency disease or HIV infection) or abnormalities in mucus secretion or mucus movement (such as those with cystic fibrosis) are more likely to suffer from sinusitis.
Chronic Sinusitis
In chronic sinusitis, the membranes of both the paranasal sinuses and the nose are thickened because they are constantly inflamed. Most experts now use the term "chronic rhinosinusitis" to describe this condition, and they also recommend that the condition be divided into rhinosinusitis with or without nasal polyps. Nasal polyps are grape-like growths of the sinus membranes that protrude into the sinuses or into the nasal passages. Polyps make it even more difficult for the sinuses to drain and for air to pass through the nose.
The causes of chronic sinusitis are largely unknown. The condition often occurs in people with asthma, the majority of whom have allergies. It is possible that constant exposure to inhaled allergens that are present year-round, such as house dust mites, pets, mold (a kind of fungus), and cockroaches cause chronic inflammation of the nose and the sinuses.
An allergic reaction to certain fungi may be responsible for at least some cases of chronic sinusitis; this condition is called "allergic fungal sinusitis." At least half of all people with chronic rhinosinusitis do not have allergies, however.
Most health experts believe that chronic rhinosinusitis is not an infectious disease (like acute sinusitis). If you suffer frequent episodes of acute sinusitis, however, you may be prone to develop chronic rhinosinusitis. Other causes of chronic rhinosinusitis may be an immune deficiency disorder (for example, primary immune deficiency disease or HIV infection) or an abnormality in the quality of mucus produced by the respiratory system (cystic fibrosis).
Another group of people who may develop chronic sinusitis are those with significant anatomic (structure) variations inside the nose, such as a deviated septum, that lead to blockage of mucus.
back to top