Sinusitis means your sinuses are infected or inflamed.  Your frontal sinuses are over the eyes under your eyebrows and your maxillary sinuses are inside each cheekbone.  These are the most commonly affected sinuses.

Anything that causes a swelling in the nose—an infection, an allergic reaction, or another type of immune reaction—also can affect your sinuses.  Air trapped within a blocked sinus, along with pus or other liquid material may cause pressure on the sinus wall. The result is the sometimes intense pain of a sinus attack.  Most cases of sinusitis start with a common cold, which is caused by a virus. Colds can inflame your sinuses and cause symptoms of sinusitis. Both the cold and the sinus inflammation usually go away without treatment within 2 weeks. If the inflammation produced by the cold leads to a bacterial infection, however, then this infection is what doctors call sinusitis.