What causes otitis media (ear infection)?

An ear infection (acute otitis media) is most often a bacterial or viral infection that affects the middle ear, the air-filled space behind the eardrum that contains the tiny vibrating bones of the ear. Children are more likely than adults to get ear infections. Ear infections frequently are painful because of inflammation and buildup of fluids in the middle ear.

The symptoms of an ear infection include the following:

(1) Earache is common but does not always occur.
(2) Dulled hearing may develop for a few days.
(3) High temperature (fever) is common.
(4) Children may feel sick or vomit and can be generally unwell.
(5) Young babies cannot point to their pain. One of the causes of a hot, irritable, crying baby is an ear infection.
(6) Sometimes the eardrum bursts (perforates). This lets out infected mucus and the ear becomes runny for a few days. A perforated eardrum usually heals within a few weeks after the infection clears.

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.

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. Swelling, inflammation and mucus in the eustachian tubes from an upper respiratory infection or allergy can block them, causing the accumulation of fluids in the middle ear. A bacterial or viral infection of this fluid is usually what produces the symptoms of an ear infection.

Ear infections are more common in children, in part, because their eustachian tubes are narrower and more horizontal — factors that make them more difficult to drain and more likely to get clogged.

According to Mayo Clinic, conditions of the middle ear that may be related to an ear infection or result in similar middle ear problems include the following:

(1) Otitis media with effusion is inflammation 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 resolved or because of some dysfunction or noninfectious blockage of the eustachian tubes.

(2) Chronic suppurative otitis media is a persistent ear infection that results in tearing or perforation of the eardrum....