Respiratory system Upper respiratory tract infection Infection and inflammation of the sinuses is known as sinusitis. Sinuses are air field cavities located in the face and skull. Explain the Etiology/causes of sinusitis. Viral infectionBacterial infectionDue to dental sepsisAllergiesNasal polypsStructural problem (deviated nasal septum)Immune system disordersChanges in the Temperature and Air. Explain the Classification of sinusitis. Sinusitis is classified based on its duration and severity as follows. On the basis of