What is sinusitis? Sinusitis, commonly called a sinus infection, is an inflammation and infection of the air-filled spaces that are located within the bones in and around the nose (paranasal sinuses). This results in swelling of the mucus membranes that line the sinuses, pain and pressure in and around the eyes and cheekbones, and a thick green discharge from the nose. Sinusitis is a common condition that is caused by a viral infection, bacterial infection, or rarely, a fungal infection. Sinusitis occurs when the body’s immune system is unable to stop harmful bacteria, viruses or fungi from reproducing in the sinuses. Fungal infections are more commonly seen in individuals with diabetes or who are compromised immune systems. Sinusitis can also be caused by allergies and autoimmune diseases. Treatment for sinusitis varies depending on the cause, severity of symptoms, presence of complications, and a person’s medical history. Treatment may include a humidifier, medications or possibly surgery. In some cases, sinusitis can spread from the sinuses to the nervous system and lead to life-threatening infections and complications, such as meningitis and brain abscess. Seek prompt medical care if you develop symptoms of sinusitis or if you have sinusitis that is not getting better. Seek immediate medical care (call 911) if you, or someone you are with, have symptoms of sinusitis that are accompanied by a change in alertness or consciousness, double vision, a seizure, or a stiff neck.