What causes frequent sinus infections?

Freq sinus infection: The most common contributor to sinus infections is nasal mucosa inflammation from viral URI (cold) and untreated or uncontrolled environmental allergies and hay fever. Smoking, structural problems in the nose such as septal deviation, turbinate anomaly or enlargement, nasal polyps and foreign material (kids) increase risk of infections.

Usually viruses but: Recurring sinus infections are more often due to virus(and not bacteria)..They can be caused by frequent exposure to others who have respiratory infections(ie, teachers, students) ;or having underlying allergies; have some "anatomic" issues with your nasal and sinus passages; or rarely a "minor" immune problem. See an allergist for a careful evaluation. There are many good treatment options.