Your sinuses are behind your cheekbones and forehead and around your eyes.
Healthy sinuses drain almost a quart of mucus every day.
They keep the air you breathe wet. Your sinuses can't drain right if they are infected and swollen. Your doctor can tell if you have a sinus infection with a physical exam, a laboratory study of a sample of your nasal discharge and X-rays of the sinuses. These work to clear the infection and reduce congestion. A cool-mist humidifier can help.