Causes

An ear infection is caused by a bacterium or virus in the middle ear. This infection often results from another illness — cold, flu or allergy — that causes congestion and swelling of the nasal passages, throat and eustachian tubes.

Role of eustachian tubes

The eustachian tubes are a pair of narrow tubes that run from each middle ear to high in the back of the throat, behind the nasal passages. The throat end of the tubes open and close to:

• Regulate air pressure in the middle ear
• Refresh air in the ear
• Drain normal secretions from the middle ear

Swollen eustachian tubes can become blocked, causing fluids to build up in the middle ear. This fluid can become infected and cause the symptoms of an ear infection.

In children, the eustachian tubes are narrower and more horizontal, which makes them more difficult to drain and more likely to get clogged.

Role of adenoids

Adenoids are two small pads of tissues high in the back of the nose believed to play a role in immune system activity.

Because adenoids are near the opening of the eustachian tubes, swelling of the adenoids may block the tubes. This can lead to middle ear infection. Swelling and irritation of adenoids is more likely to play a role in ear infections in children because children have relatively larger adenoids compared to adults.

Related conditions

Conditions of the middle ear that may be related to an ear infection or result in similar middle ear problems include:

• Otitis media with effusion, or swelling and fluid buildup (effusion) in the middle ear without bacterial or viral infection. This may occur because the fluid buildup persists after an ear infection has gotten better. It may also occur because of some dysfunction or noninfectious blockage of the eustachian tubes.
• Chronic otitis media with effusion, occurs when fluid remains in the middle ear and continues to return without bacterial or viral infection. This makes children susceptible to new ear infections and may affect hearing.
• Chronic suppurative otitis media, an ear infection that doesn't go away with the usual treatments. This can lead to a hole in the eardrum.