An ear infection occurs when one of the Eustachian tubes becomes swollen or blocked, causing fluid to build up in the middle ear. Eustachian tubes are small tubes that run from each ear directly to the back of the throat. The causes of eustachian tube blockage include allergies, colds, sinus infections, excess mucus, smoking, infected or swollen adenoids (tissue near the tonsils that trap harmful bacteria and viruses) and changes in air pressure.
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