Ear infections include a broad range of diseases that can affect any of the ear structures. A middle ear infection (otitis media) is an inflammation or infection of the middle ear and is the focus of this topic. This condition is most common in young children, because their Eustachian tubes (the tubes that connect the throat and the middle ear) are shorter, more horizontal, and more easily blocked than those in older children and adults. A middle ear infection frequently occurs along with or after a cold or other upper respiratory infection. The space in the middle ear, behind the eardrum, is normally filled with air. Any accumulation of fluid in the middle ear space is called an effusion. This fluid provides an environment that allows infection to develop.

There are three types of ear infections:

1. An infection involving the outer parts of the ear, such as "swimmer's ear," is called otitis externa.
2. An infection involving the hearing parts of the inner ear is called otitis interna.
3. There are two types of middle ear infection, or otitis media. Acute otitis media is an inflammation of the lining of the middle ear space that can result in the accumulation of fluid in the space and infection. Otitis media is associated with a rapid onset of symptoms, including ear pain and fever. Otitis media with effusion is a buildup of fluid in the middle ear behind the eardrum without symptoms of infection.