Some common causes of chronic sinusitis are listed below.
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Allergies or asthma: Asthma or allergies can cause inflammation and block sinuses.
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Underlying medical conditions: Cystic fibrosis and diseases that weaken the the immune system, e.g., HIV, can lead to nasal blockage.
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Nasal polyps: Abnormal growths in the nasal passages can caused blocked sinuses.
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Deviated nasal septum: The wall between the nostrils, i.e., nasal septum, can become deviated. The deviated septum can restrict air flow in one of the nostrils, causing blocked sinus.
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Respiratory infections: Bacterial infections, viral infections, or fungal infections can cause swelling and block mucus drainage.