A mastoid infection, also known as mastoiditis, occurs when bacteria infect the mastoid bone, located behind the ear. This condition often develops as a complication of an untreated middle ear infection or otitis media. Symptoms may include ear pain, swelling behind the ear, fever, and drainage from the ear. If left untreated, mastoid infections can lead to serious complications, such as hearing loss or the spread of infection to nearby structures. Diagnosis typically involves a physical examination and imaging tests, while treatment usually includes antibiotics and, in some cases, surgery to drain the infected area.