Healthy, non infected sinuses are filled with air. However, if the sinuses become blocked and filled with fluid, they can become infected, which is a condition known as sinusitis. This infection is very common; about 35 million people in the United States have it at least once a year.
Acute sinusitis usually starts suddenly and lasts for 2-4 weeks. Subacute sinus inflammation can last 4-12 weeks. Chronic inflammation last for more than 12 weeks. Recurrent sinusitis occurs several times a year .
Causes of sinusitis include:
- the common cold
- blocked drainage ducts
- structural differences narrowing those ducts
- nasal polyps
- immune system deficiencies (could be caused by medications)