The pain experienced with sinusitis is usually caused by a blockage of the sinus opening, which could be caused by infections, irritants, allergies or a structural abnormality.
Infections
Adults can suffer from a cold or upper respiratory tract infection up to three times a year, with children getting them more regularly. Following a cold, when mucus turns yellow or green as opposed to clear it is a sign of a bacterial infection, which, in addition to viral infection, can cause swelling of the lining of the nose and thickening of the normal mucus. Sinus infection may occur as a result of this as it inhibits proper sinus drainage.
Irritants
Swelling of the lining of the nose can also be caused by irritants like air pollution, smoke and chemical irritants (e.g. some sprays containing pesticides), disinfectants and household detergents. Again, this can impair sinus drainage through narrowing or blocking the opening to the sinuses and in turn causing infection.
Allergies
Allergies can cause inflammation inside the nose as common symptoms of an allergic reaction include nasal stuffiness, runny nose, sneezing and itchy watery eyes. Chronic sinusitis is sometimes associated with asthma and allergies are responsible for asthma in some patients. The nasal stuffiness experienced with allergies makes asthma more difficult to control.
Structural abnormality
Narrowing of the nasal cavity can sometimes be caused by structural problems as a result of trauma or developed when growing. If the narrowing is severe then it causes a blockage with mucus building up behind it and leading to infection.