Sinusitis – inflammation of the mucous membrane of one or more paranasal sinuses. It can occur as a complication of acute rhinitis, influenza, other infectious diseases, as well as after injuries to the facial area. Sinusitis can be caused by both viruses and bacteria. The main symptoms are heaviness in the paranasal or frontal area, pain with sudden head movements, thick nasal discharge, and fever. In children, the development of sinusitis should be suspected if, after a runny nose subsides, the temperature rises again after a few days and thick nasal discharge appears. The diagnosis of sinusitis is most often made in children aged 3-15 years.