What Causes Sinusitis?
Sinusitis, or inflammation of the paranasal sinuses, arises from a complex interplay of anatomical, infectious, inflammatory, and environmental factors. The most common initiating event is viral upper
Sinusitis, or inflammation of the paranasal sinuses, arises from a complex interplay of anatomical, infectious, inflammatory, and environmental factors. The most common initiating event is viral upper respiratory infection—such as those caused by rhinovirus, influenza virus, or SARS-CoV-2—which triggers mucosal swelling, impairs ciliary clearance, and obstructs sinus ostia. This obstruction leads to mucus stasis, creating an ideal environment for secondary bacterial colonization.
Bacterial pathogens—including Streptococcus pneumoniae, Haemophilus influenzae, and Moraxella catarrhalis—are responsible for the majority of acute bacterial sinusitis cases, typically emerging after 7–10 days of persistent or worsening symptoms. Chronic sinusitis (lasting ≥12 weeks) involves more nuanced mechanisms: persistent type 2 inflammation (often associated with eosinophilia, nasal polyps, and comorbid asthma), biofilm formation, dysbiosis of the sinonasal microbiome, and structural abnormalities such as septal deviation or concha bullosa that compromise sinus ventilation and drainage.
Other contributing factors include allergic rhinitis, cystic fibrosis, primary ciliary dyskinesia, immunodeficiency states (e.g., IgA deficiency or HIV), dental infections (particularly involving the maxillary molars and premolars), and exposure to irritants like tobacco smoke or occupational pollutants. In rare cases, fungal sinusitis—either allergic, chronic invasive, or acute fulminant—may occur, especially in immunocompromised individuals.
Accurate diagnosis hinges on clinical assessment, including symptom duration, pattern of progression, and physical findings such as purulent nasal discharge or facial tenderness. Imaging and endoscopy are reserved for refractory, recurrent, or complicated cases. Management is tailored to the underlying etiology and severity, ranging from supportive care and intranasal corticosteroids to targeted antimicrobials, biologics for type 2 inflammation, or functional endoscopic sinus surgery when medical therapy fails.