1. Anything interfering with airflow into and drainage of mucus out of the sinuses can cause sinusitis.
2. The sinus openings may be obstructed by anything, causing swelling of tissue lining the ostia and adjacent nasal passage, such as colds, allergies and tissue irritants (such as over-the-counter nasal sprays, cigarette smoke and recreational substances snorted through the nose).
3. Allergies may complicate sinusitis.
Read: Sinus alert
4. Drainage of mucus can be impaired by thickening of secretions, decrease in mucus hydration (water content) because of disease, drying medications (antihistamines), and lack of air humidity.
5. Irritants, especially smoke, may damage cilia, and prevent them from assisting with mucus drainage. Stagnated mucus provides an ideal environment for bacteria and in some cases (such as AIDS) fungus to grow.
6. Other irritants include car exhaust, petrol and paint fumes, perfume, insect spray and household chemicals.
Read: Managing sinusitis
7. Sinuses can become obstructed by tumours or growths. Nasal polyps (growths arising from mucous surfaces), probably caused by nasal inflammation, can block the ostia.
8. Occasionally, immune problems cause sinus infections. If you have persistent sinus infections, have your immune system evaluated by an allergist/immunologist, especially before surgery is done. You may need allergy tests, and tests to ensure you can form antibodies to common bacteria normally. Sinusitis can be due to AIDS, although only an extremely small percentage of people with sinusitis have AIDS.