The mucous can become thickened from dehydration and the cilia fail to tranport it to the otium. The mucous normally has two layers, an inner sol layer and a more viscous outer gel layer. The cilia sweep most effectively against the sol layer. With dehydration, the sol layer decreases and the cilia may come in contact with the gel layer. This causes poor transport and a backup of mucous, leading to infection.
Gravity can draw the mucous into the lower regions of the sinus where it can become infected.
These include smoking and exposure to cigarette smoke, allergies, low humidity, and some antihistamines. The cilia can also be damaged by infections or inflammation. Certain systemic illnesses like cystic fibrosis and immotile cilia syndrome are associated with ciliary dysfunction. Any blockage to the outflow of mucous will lead to its buildup in the sinus and increased risk of infection. Allergies or viral infections can produce mucosal edema and subsequent obstruction.