During normal respiration, air travels through the nose and into the lungs. Inside the bones of the skull are air pockets called sinuses. The four major sinuses that drain into the nose and throat are the frontal, maxillary, ethmoid, and sphenoid.
Sometimes foreign particles get past the cilia of the nose and enter one of the four sinus cavities.
The sinuses are also equipped with cilia that push mucous and particles out of the sinus cavities. The sinuses then drain into the nose through a hairpin-shaped tube called the ostium. If the cilia are unable to push the mucus through the ostium, mucus can collect in the sinuses, blocking the pathways and causing swelling and inflammation of the membranes lining the sinuses- a condition called sinusitis.
Sinusitis often develops following an upper respiratory infection or allergic reaction. Symptoms of sinusitis can include facial pain or pressure, nasal obstruction, nasal discharge, and dental pain. Over-the-counter and prescription medications can help alleviate the symptoms of sinusitis; however, long term sufferers may require surgery.