The sinus cavities include:
• The maxillary sinuses (the largest), in the cheekbones.
• The frontal sinuses, in the low-center of the forehead.
• The ethmoid sinuses, between the eyes, at the nasal bridge.
• The sphenoid sinuses, in bones behind the nasal cavity.
The sinuses are lined with soft, pink tissue called mucosa. Normally, the sinuses are empty except for a thin layer of mucus.
The inside of the nose has ridges called turbinates. Normally these structures help humidify and filter air. The nose is divided in the center by a thin wall, called the septum. Most of the sinuses drain into the nose through a small channel or drainage pathway called the middle meatus.
The purpose of the sinuses is unclear. One theory is that sinuses help humidify the air we breathe in; another is that they enhance our voices.
There are millions of bacteria in our noses, and most of the time, they’re harmless. Even when a few creep into the sinuses, they don’t cause trouble, as long as they keep draining into the nose along with mucus. But if sinus drainage is blocked, glands in the sinuses continue to produce mucus, and the resulting pool of backed-up mucus provides what Dr. Metson calls “the perfect culture medium.” The bacteria grow out of control, causing infection, and the immune system kicks off an inflammatory response. The result: swelling, which causes headache and facial pain; mucus buildup, which produces congestion; and an influx of white blood cells to fight the bacteria, which thickens the mucus and may tint it yellow or green. Other symptoms include loss of smell or taste, cough, bad breath, fever, toothache, and fullness in the ears.Sinus blockage can have a variety of environmental, anatomical, and genetic causes, but the main culprit is swelling of the nasal passages produced by the common cold or allergies. More serious sinusitis can result from structural problems, such as a deviated septum (a crook in the partition that separates the right from left nasal cavities) or nasal polyps (small, grapelike growths in the lining of the sinus cavity).