Sinusitis is a common condition in which the lining of the sinuses becomes inflamed. It’s usually caused by a viral infection and often improves within two or three weeks.

The sinuses are small, air-filled cavities behind the cheekbones and forehead.

The mucus produced by the sinuses usually drains into the nose through small channels. In sinusitis, these channels become blocked because the sinus linings are inflamed (swollen).