Sinusitis, sometimes called a sinus infection, is an inflammation of the paranasal sinuses, the air filled cavities that surround the nose. The mucus membrane lining the sinuses normally produces mucous to help filter, warm, and humidify the air we breathe. When this lining becomes inflamed, the sinuses fill with fluid and eventually become clogged, preventing normal mucus drainage. This can cause pain and pressure in the face and behind the eyes, difficulty breathing through the nose, and drainage of mucus into the back of the throat called postnasal drip.

Sinusitis has several possible causes but it occurs most commonly as a complication of the common cold. It can also be caused by other types of respiratory infections or by allergies. Sinusitis can be acute, meaning it lasts for less than four weeks or chronic, when it recurs or lasts for more than twelve weeks.

Sinusitis is very common, affecting an estimated 40 million Americans each year and costing billions of dollars in medical care and lost productivity. In many cases, sinusitis can be treated with antibiotics or other medications but in other cases surgery may be required.