What is Sinusitis (sinus infection)?

Sinusitis is inflammation of the sinuses, the air-filled spaces behind the nose, forehead, and cheeks, most often triggered by a cold or allergy. It causes facial pain or pressure, a blocked or runny nose, reduced sense of smell, and sometimes a cough that's worse at night.

Most cases are caused by viruses and settle within two to three weeks, though a bacterial infection can occasionally develop, particularly if symptoms are severe or persist beyond this.