What Is It?
Sinuses are air-filled spaces behind the bones of the upper face: between the eyes and behind the forehead, nose and cheeks. The lining of the sinuses are made up of cells with tiny hairs on their surfaces called cilia. Other cells in the lining produce mucus. The mucus traps germs and pollutants and the cilia push the mucus out through narrow sinus openings into the nose.
When the sinuses become inflamed or infected, the mucus thickens and clogs the openings to one or more sinuses. Fluid builds up inside the sinuses causing increased pressure. Also bacteria can become trapped, multiply and infect the lining. This is sinusitis.