The membranes can become so swollen that the tiny openings from the sinuses become blocked. When mucus and air cannot flow easily between the nose and sinuses, abnormal pressures occur in the sinuses, and mucus can build up in them. This creates a pressure-pain in the forehead or face, between and behind the eyes, or in the cheeks and upper teeth, depending on which sinuses are involved. A blocked sinus cavity filled with mucus becomes a fine place for bacteria to grow. The pressure and pain in the face and forehead can be quite severe in acute bacterial sinusitis.
Chronic sinusitis occurs when the sinus opening is blocked for an extended period.
Headaches are less prominent in chronic sinusitis, but congestion and unpleasant nasal secretions usually persist. Also, fleshy growths known as polyps can develop as an exaggerated form of inflammatory swelling of the membranes. Some cases of sinusitis come from infections in the upper teeth that extend into the sinuses. Most cases of sinusitis respond promptly to medical treatment and are not serious. However, an infection that is in the sinus is also very close to the eye and to the brain.