Sinusitis
Sinusitis is an inflammation, or swelling, of the tissue lining the sinuses. Normally, sinuses are filled with air. But when they become blocked and filled with fluid, germs (bacteria, viruses, and fungi) can grow and cause an infection.
Conditions that can cause sinus blockage include the common cold, allergic rhinitis (swelling of the lining of the nose), nasal polyps (small growths in that lining), or a deviated septum (a shift in the nasal cavity).