The sinuses are hollow spaces in the bones behind the face. Directly behind the nose is the nasal cavity. On either side of the nasal cavity are large sinuses. A row of very small sinuses runs behind the bridge of the nose, and two more large sinuses are located above and behind the inner part of the eyebrows.
Sinusitis is inflammation of the sinuses. It may be associated with both bacterial and viral infections, but it may be due to non-infectious inflammation (e.g., allergies) in the sinuses as well. Sinusitis can be acute, lasting less than 4 weeks, or chronic, lasting 8 to 12 weeks or more. Acute sinusitis is very common, affecting about 1 in 10 people each year.
People with asthma, cystic fibrosis, and allergies are more likely to get sinusitis, as are those who have had their nose broken previously and those who were born with a malformed septum (the dividing wall between the nostrils). People with diabetes or those who are immunocompromised are at increased risk for complications of sinusitis.