The most common cause of sinusitis is a condition causing partial or complete obstruction of the tiny openings into the sinuses known as ostia – but particularly swelling of the nasal turbinates (sausage shaped bony structures covered by spongy mucous membranes in the nasal cavities).
In other words, anything interfering with airflow into and drainage of mucus out of the sinuses can cause sinusitis.
• Many things can obstruct the sinus openings, i.e. upper respiratory tract infections (e.g. colds), allergies, cigarette smoke and especially hay fever.
• Dust, pollen, animal hair, house-dust mites, some over-the-counter nasal sprays and cigarette smoke can all irritate the mucous membranes and lead to hay fever. Dry air does the same, as can exhaust gases, petrol and paint fumes, perfume, insecticides and household cleaners.
• Irritants, especially smoke, may damage cilia, and prevent them from assisting with mucus drainage. Stagnated mucus provides an ideal environment for bacteria to grow.
• 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.
• Sinuses can become obstructed by tumours or growths. Nasal polyps (growths arising from mucous surfaces), probably caused by nasal inflammation, can block the ostia.
• Occasionally, immune problems cause sinus infections. If you have persistent sinus infections, have your immune system evaluated by an allergist/immunologist, especially before surgery. You may need allergy tests and tests to ensure you can form antibodies to common bacteria in a normal way. Sinusitis can be caused by AIDS, although only an extremely small percentage of people with sinusitis have AIDS.
Reviewed by Dr Harris Steinman MBChB. (UCT), D.CH (SA), FAAAAI, D.Av.Med.(SAMS), Private specialist at FACTS (Food & Allergy Consulting & Testing Services), February 2015. (Previously updated by Dr H Steinman, June 2007)