Sinusitis What is Sinusitis? Before we try to understand what sinusitis is, let us first understand what sinuses are. Sinuses are spaces in the bones in the front part of the face: in the forehead; between the eyes, in the cheeks; and behind the eyes, and they’re air-filled spaces with a membranous lining, and the lining produces mucus. The mucus drains from the sinuses into the nose through…