by Eric Lannak

Created on: May 16, 2010

Sinusitis is an inflammation of the paranasal sinuses (bony cavities in your face that connect to your nose) that's usually caused by infection, but is sometimes caused by allergies, fungal growth, and even autoimmune reactions. Though the term “sinusitis” is commonly used, it's largely been replaced in medical literature by “rhinosinusitis” (“rhino” is Latin for “nose”, and was added to reflect the nasal passages’ involvement).

WHAT ARE SINUSES?

Sinus means “empty cavity”, and there are many sinuses in the human body. “Paranasal sinuses” is doctorspeak for the four pairs of chambers in your face; the maxillary sinuses (one in each cheekbone), the frontals (one behind each eyebrow), the ethmoids (a pair right next to each other under the bridge of the nose), and the sphenoids (next to each other behind the ethmoids).

These chambers connect to your nose by way of tiny openings the size of a grape seed called “ostia” (or “ostium” in the singular). Each sinus has only one ostium, and it’s the only way anything gets in or out without passing through the chamber wall.

A bad cold that produces funny-colored nasal mucous, blocks your ears, makes you cough odd-colored matter, or blocks your nose for weeks on end is not a cold. It’s sinusitis.

HOW DO THEY GET INFECTED?

The sinuses are lined with mucous membranes that produce a lot of the quart-a-day of mucous your nose uses. This ooze normally forms a thin film coating the sinuses’ interior walls, where it’s swept toward the ostia and out into the nasal passages by microscopic whip-like structures called “cilia” that sprout from the membrane. The cilia flail ceaselessly to keep the goo moving, and the sinuses are kept nearly sterile because the mucous layer is pushed out and replaced three times an hour.

But sometimes the process fails. An obstructed ostium (from nasal swelling, for example) will block mucous passage, and instead of flowing into the nose the stuff backs up and pools in the chamber. Likewise if something (like a drug reaction or a viral infection) slows the cilia, they can’t clear the sinus effectively, and excess mucous will accumulate.

The list of things that can disrupt mucous clearance is long, including not only those already mentioned but also nasal polyps (common in allergy sufferers), anatomical issues (like small ostia or a badly deviated

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