Most of us have had a sinus infection at some point. These infections—called sinusitis—happen when the sinuses (the air-filled spaces behind your nose and cheeks) become inflamed or blocked. Mucus builds up, causing pressure, pain, drainage, and that stuffy feeling. These infections are usually self-limited or resolve with medications in a short time frame. Chronic sinusitis is different from a standard sinus infection. It’s defined as nasal and sinus inflammation that lasts 12 weeks or longer, even with treatment. For some people, symptoms can last months or even years.