It is the condition where the sinuses or more accurately, the lining of the sinuses is inflamed. Sinuses are cavities present in the skull to provide balance to the adjacent structures and drain mucus, thus keeping the head and nose free of bacteria. There are almost 8 sinuses in the head. This inflammation leads to pain near the head, neck, eyes, difficulty in talking, blocked nose, and heavy feeling in the head. The condition is generally triggered by allergens. It can also be caused by nasal septum deviation. Based on its onset and occurrence, it can be acute, chronic or subacute.