Sinusitis
Sinusitis is the inflammation of the sinuses; it's usually
caused by an allergic reaction or an infection in your sinuses that stops them
from working properly. The sinuses are air-filled spaces behind the bones of
your face that open up into the nose cavity. They are lined with the same
membrane as your nose. They make mucus, which normally drains through small
openings into your nose. Any of your sinuses can get blocked and inflamed,
leading to sinusitis.