Sinus Infection Causes

Acute sinusitis usually follows a viral infection in the upper respiratory tract, but allergy-causing substances (allergens) or pollutants may also trigger acute sinusitis. Viral infection damages the cells of the sinus lining, leading to inflammation. The lining thickens, obstructing the nasal passage. This passage connects to the sinuses. The obstruction disrupts the process that removes bacteria normally present in the nasal passages, and the bacteria begin to multiply and invade the lining of the sinus. This causes the symptoms of sinus infection. Allergens and pollutants produce a similar effect.

Bacteria that normally cause acute sinusitis are Streptococcus pneumoniae, Haemophilus influenzae, and Moraxella catarrhalis. These microorganisms, along with Staphylococcus aureus and some anaerobes (bacteria that live without oxygen), are involved in chronic sinusitis.

Fungi are also becoming an increasing cause of chronic sinusitis, especially in people with diseases that weaken the immune system, such as AIDS, leukemia, and diabetes.