Sinusitis is a condition that occurs when the lining of the sinuses becomes inflamed or swollen. The sinuses are small, air-filled spaces in the cheekbones and forehead. When the sinuses become inflamed, mucus can't drain normally into the nose, leading to a buildup of mucus or blocked sinuses.

Sinusitis is present when the tissue lining the sinuses become swollen or inflamed. It occurs as the result of an inflammatory reaction or an infection from a virus, bacteria, or fungus.Acute sinusitis is most often caused by the common cold. Signs and symptoms may include a blocked and stuffy (congested) nose, which may block your sinuses and prevent drainage of mucus. Acute sinusitis is an infection caused by a virus. The common cold is most often the cause.