Sinusitis
Sinusitis, or sinus infection, is an inflammation of the sinuses. The sinuses are air-filled spaces located in the upper jaw and forehead. During an infection, the sinus lining swells, preventing fluid drainage from the sinus cavity. This causes a painful and pressure-like sensation. In most cases, sinusitis is a benign condition. In very rare instances, it can be dangerous due to the proximity of the sinuses to the brain.