Causes

Most cases of acute sinusitis are preceded by virus-induced "colds." These viral "colds" do not cause symptoms of sinusitis, but they do cause inflammation of the sinuses. Both the "cold" and the sinus inflammation usually resolve without treatment in two weeks. However, the inflammation might explain why colds increase the likelihood of developing acute sinusitis. For example, the nose reacts to an invasion by viruses that cause infections such as the common cold, flu, or measles by producing mucus and sending white blood cells to the lining of the nose, which congest and swell the nasal passages. When this swelling involves the adjacent mucous membranes of the sinuses, air and mucus are trapped behind the narrowed openings of the sinuses. If the sinus openings become too narrow to permit drainage of the mucus, then bacteria, which normally are present in the respiratory tract, begin to multiply. Most healthy people harbor bacteria, such as Streptococcus pneumoniae and Haemophilus influenzae, in their upper respiratory tracts with no ill effects until the body's defenses are weakened or drainage from the sinuses is blocked by a cold or other viral infection. The bacteria that may have been living harmlessly in the nose or throat can multiply and cause an acute sinus infection.

Sometimes, fungal infections can cause acute sinusitis. Although these organisms are abundant in the environment, they usually are harmless to healthy people, indicating that the human body has a natural resistance to them. Fungi, such as Aspergillus, can cause serious illness in people whose immune systems are not functioning properly. Some people with fungal sinusitis have an allergic-type reaction to the fungi.

Chronic inflammation of the nasal passages (rhinitis) also can lead to sinusitis. Allergic rhinitis or hay fever (discussed below) may be complicated by episodes of acute sinusitis. Patients with allergic rhinitis also often have chronic sinusitis. Vasomotor rhinitis, caused by humidity, cold air, alcohol, perfumes, and other environmental conditions, also may be complicated by sinus infections.

Acute sinusitis is much more common in certain patients than in the general population. For example, sinusitis occurs more often in patients with reduced immune function (such as patients with immune deficiencies and HIV infection) and with abnormality of mucus secretion or mucus movement (such as cystic fibrosis and diseases of abnormal cilia [Kartagener's syndrome]).

Chronic Sinusitis
Diagnosis
Treatment
Prevention
Additional Information

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Sources:
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