Sinusitis refers to inflammation of the sinuses, which are hollow cavities in the skull. It is usually caused by viral, bacterial, or fungal infections. There are different types of sinusitis including acute, subacute, chronic, and recurrent. Symptoms include coughing, nasal discharge, stuffy nose, headache, and facial pressure. Sinusitis can be prevented by avoiding irritants like smoke and maintaining good indoor air quality. Treatment depends on the type but may involve saline rinses, decongestants, antibiotics, or surgery to address underlying causes in chronic cases. Untreated sinusitis can lead to serious infections like meningitis.