Anything "-itis" means it is inflamed.
Causes of inflammation
include allergic, chemical (inhaled irritating fumes), mechanical/traumatic, and infectious. If the sinuses are inflamed and swollen, this often leads to a swelling shut of the sinus cavities in the cheeks, nose, and forehead, causing pressure and pain, which can predispose them to infection. See your internist if saline rinses fail.