Final answer:
Sinusitis is the inflammation of the membranes lining the sinus cavities caused by infection or allergies.
Step-by-step explanation:
The inflammation of the membranes lining the sinus cavities caused by either infection or allergies is diagnosed as sinusitis. Sinusitis is an inflammation of the paranasal sinuses, which are hollow, air-filled spaces located within certain bones of the skull. Sinusitis can be caused by bacteria or viruses and may result in symptoms such as nasal congestion, facial pain, and headache.