The sinuses are bony hollows in the head. When the lining of the nose and sinuses becomes swollen with allergies or infections, the sinuses can become obstructed. If they stay obstructed long enough, the mucus in the sinuses can become infected. When this occurs, patients typically experience facial pain in the distribution of the sinuses, as well as thickened, often yellow or green, nasal discharge, as well as nasal congestion.

A variety of other symptoms can occur with sinusitis, including runny itchy eyes, cough, ear symptoms including discomfort or a sense of fullness in the ears, hoarseness, and a bad smell in the nose. Sinus swelling can lead to the formation of nasal polyps. Nasal polyps, in turn, tend to obstruct sinuses and lead to sinusitis.

Facial pain, in isolation, can have other causes, including temporomandibular joint syndrome (TMJ), dental disease and non-sinus headache.