Rhinosinusitis

Rhinosinusitis is inflammation of the nasal cavity and paranasal sinus mucosa. A viral upper-respiratory infection is the usual trigger. Inflammation causes mucosal oedema, which narrows or closes the sinus ostia—the small drainage openings that connect the sinuses with the nasal cavity. Once drainage is obstructed, mucociliary clearance becomes ineffective, secretions stagnate, and pressure develops. Most episodes remain viral and improve with supportive treatment. Bacterial infection can follow when impaired clearance creates conditions for bacterial overgrowth. This is why symptom trajectory matters more than mucus colour alone: purulent discharge may occur with inflammation, but bacterial disease is more likely when purulence is paired with a characteristic duration or deterioration pattern. Allergic rhinitis, nasal polyps, a deviated septum, smoking, dental disease, cystic fibrosis, and immune compromise can increase the risk by promoting inflammation, obstruction, or impaired clearance. These factors increase susceptibility; they do not by themselves establish an acute bacterial infection.