What is acute sinusitis? Acute sinusitis is inflammation of the sinuses, which are the hollow spaces in the skull. The inflammation is most commonly caused by several different infectious organisms including bacteria, viruses or fungi. Most commonly, acute sinusitis is the result of inflammation, congestion and blockage caused by a cold or allergy. Acute sinusitis can also result from sinus blockage due to a deviated nasal septum, nasal bone spur, or nasal polyps. The inflammation of the sinuses in acute sinusitis prevents nasal hairs (cilia) from removing mucus, resulting in blockage and infection. Most commonly, people develop acute sinusitis from colds and allergies that may cause too much mucus to be made or that block the opening of the sinuses. Less common causes of acute sinusitis include decongestant nasal spray abuse, smoking, swimming, or diving. Left untreated, acute sinusitis may lead to sinus abscess formation. It can trigger severe asthma, or lead to meningitis. Seek immediate medical care (call 911) for serious symptoms, such as high fever (higher than 101 degrees Fahrenheit), difficulty breathing, or changes in vision. Seek prompt medical care if you are being treated for acute sinusitis but mild symptoms recur or are persistent.