Sinus infection, or sinusitis, is an inflammation of the sinuses and nasal passages. A sinus infection can cause pain or pressure in the eyes, nose, cheek area, or on one side of the head. A person with a sinus infection may also have a cough, a fever, bad breath, and nasal congestion with thick nasal secretions. Sinusitis is categorized as acute (sudden onset) or chronic (long term, the most common type).

Anatomy of the sinuses (also called paranasal sinuses): The human skull contains four major pairs of hollow air-filled-cavities called sinuses. These are connected to the space between the nostrils and the nasal passage. Sinuses help insulate the skull, reduce its weight, and allow the voice to resonate within it. The four major pairs of sinuses are the:

Picture of the anatomy of the sinuses

The sinuses contain defenses against foreign viruses and bacteria (germs). If the normal defenses are disrupted, they may allow bacteria normally present in the nasal passages to enter any of the sinuses. Once there, the bacteria may cause a sinus infection.

Acute sinusitis usually lasts less than eight weeks or occurs no more than two times per year with each episode lasting no longer than 10 days. Medications are usually effective against acute sinusitis. Successful treatment counteracts damage done to the mucous lining of the sinuses and surrounding bone of the skull.

Chronic sinusitis lasts longer than eight weeks.

The sinuses are covered with a mucus layer and cells that contain little hairs on their surfaces (cilia). These help trap and propel bacteria and pollutants out of the sinus cavity. Acid reflux from the stomach can affect the sinuses in patients of age.