Sinusitis causes

Causes
The sinuses are air-filled spaces in the skull (behind the forehead, nasal bones, cheeks, and eyes) that are lined with mucus membranes. Healthy sinuses contain no bacteria or other germs. Usually, mucus is able to drain out and air is able to circulate.

When the sinus openings become blocked or too much mucus builds up, bacteria and other germs can grow more easily.

Sinusitis can occur from one of these conditions:
 * Small hairs (cilia) in the sinuses, which help move mucus out, do not work properly due to some medical conditions.
 * Colds and allergies may cause too much mucus to be made or block the opening of the sinuses.
 * A deviated nasal septum, nasal bone spur, or nasal polyps may block the opening of the sinuses.

Sinusitis can be:
 * Acute -- symptoms last 2 - 8 weeks
 * Chronic -- symptoms last much longer

Acute sinusitis is caused by damage to the lining of the sinuses from surgery or infections. Chronic sinusitis may be caused by bacteria or a fungus.