Sinusitis is inflammation of the sinus cavities. It is usually associated with infection. The sinus cavities are air-filled spaces in the skull.

Sinusitis is called acute if it lasts for less than 4 weeks, subacute if it lasts 4-12 weeks, and chronic if symptoms last for more than 3 months. You may have recurrent sinusitis if you have repeated bouts of acute sinusitis.

Sinus Infection
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Infectious sinusitis is caused by bacterial, viral, or rarely fungal infection of fluid in the sinus cavities.