Sinuses are the air-filled cavities in the bones of the face and skull. The largest sinus cavities are in the forehead and cheeks on either side of the nose. Sinusitis (sine-us-eye-tus) occurs when the sinuses become inflamed. In most cases, sinusitis results as a complication of the common cold or some other infection of the nose and throat, or may be associated with hay fever or dental problems. Thickened mucus prevents normal drainage of the sinuses, resulting in intense pain as the sinuses fill with fluid. Sinusitis may affect only one side of the head causing the affected side of the face to swell. There also may be fever, a yellowish or greenish discharge from the nose, and a decreased sense of smell. Sinusitis should be treated by a doctor who may prescribe an antibiotic or sulfa drug. Decongestants may also be prescribed. It's best to get plenty of rest and add moisture to the air with a vaporizer or humidifier. Also drink plenty of fluids, to help stay hydrated. For more information on sinusitis, contact a health care professional.