Sinusitis is an inflammation of the sinus lining. If the sinus opening becomes blocked due to this swelling, normal mucus drainage may not occur, and this may lead to recurrent sinus infections and painful symptoms. Sinusitis can be acute, lasting for less than four weeks, or chronic, lasting longer than 12 weeks. When sinus symptoms either last longer than 12 weeks, or if you experience more than 4 sinus infections each year, you should see an ENT doctor to discuss treatment options.