What is the most common predisposing factor for acute sinusitis?

The most common predisposing factor for acute sinusitis is a viral upper respiratory infection (URI). Viral infections often lead to inflammation and edema of the nasal passages and sinus mucosa, which can obstruct the sinus openings. This obstruction impairs normal mucus drainage and creates an environment that is conducive to sinus infection. Following a URI, the risk of acute bacterial sinusitis increases due to secondary bacterial infection, as organisms that reside in the nasopharynx can proliferate in the inflamed, obstructed sinus cavities.

While environmental allergies, chronic smoking, and anatomical variations can contribute to sinus issues, they are not as common as viral URIs in precipitating acute sinusitis. Allergies can cause prolonged nasal congestion and inflammation, and chronic smoking can harm the mucociliary clearance, but typically, the triggering event for acute sinusitis is associated with an initial viral infection. Thus, the association of acute sinusitis with viral upper respiratory infections is well-established and is considered the primary predisposing factor in most cases.