Fluid in the middle ear is caused by blocked or swollen eustachian tubes, according to Mayo Clinic, or as a result of congestion from colds, allergies or viral upper respiratory infections, states the CDC. Fluid in the middle ear also results from exposure to irritants such as cigarette smoke.
The eustachian tubes connect the middle ear to the back of the throat, states Mayo Clinic. When they become blocked because of swelling, inflammation, an accumulation of mucous, or the swelling of nearby adenoids, it causes fluid to build up in the middle ear, states the CDC. This fluid can then become infected by bacteria or viruses, but isn't otherwise painful and usually goes away without treatment. Fluid that is the by-product of an ear infection may remain over a month after the initial infection clears, states the CDC, or remain from three to six months, according to Group Health.
Fluid in the middle ear is more common in children than adults because of the width and position of their eustachian tubes and because their adenoids are more active and proportionally larger, according to Mayo Clinic. Children with fluid in the middle ear most likely don't experience pain or fever, according to Group Health, but may have trouble hearing properly. Fluid in the middle ear can be found during a regular checkup or through special tests performed by an audiologist.