Inflammation or infection of the middle ear occurs when the eustachian tube to that ear is blocked. The eustachian tube is the passage from the back of the throat to the middle ear. Chronic otitis media occurs when the eustachian tube becomes blocked repeatedly (or remains blocked for long periods) due to allergies, multiple infections, ear trauma, or swelling of the adenoids.

When the middle ear is actually infected with bacteria (or occasionally, viruses) rather than just inflamed, it is more serious. A chronic ear infection may be the result of an acute ear infection that does not clear completely, or the result of recurrent ear infections. The infection may spread into the mastoid bone (mastoiditis), or pressure from fluid build-up may rupture the eardrum or damage the bones of the middle ear.

A chronic ear infection may be more destructive than an acute ear infection because its effects are prolonged or repeated, and it may cause permanent damage to the ear. However, a chronic, long-term infection may show less severe symptoms -- so the infection may remain unnoticed and untreated for long periods of time.

Ear infections are more common in children because their eustachian tubes are shorter, narrower, and more horizontal than in adults. Chronic ear infections are much less common than acute ear infections.