Sinusitis' target=_blank>Sinusitis appears when the nasal membrane gets affected by pollutants, cold or dry air and becomes inflamed. Secondary the cilia will slow down their movements, and mucus will be mass produced in order to eliminate the accumulated bacteria. Because cilia are not working properly the mucus will be trapped in the sinuses and cause a local infection. Sometimes even the fact that the secretions are thick can cause sinusitis. In rare cases a tumor can block the sinuses causing a local obstruction.