Middle Ear Infections

A Close Look at the Ear

Next to the common cold, ear infections are the most commonly diagnosed childhood illness in the United States. More than 3 out of 4 kids have had at least one ear infection by the time they reach 3 years of age. To understand how ear infections develop, let's review how the ear works.

Think about how you can feel speakers vibrate as you listen to your favorite CD in the car or how you feel your throat vibrate when you speak. Sound, which is made up of invisible waves of energy, causes these vibrations. Every time you hear a sound, the various structures of the ear have to work together to make sure the information gets to the brain.

The ear is responsible for hearing and balance and is made up of three parts — the outer ear, middle ear, and inner ear. Hearing begins when sound waves that travel through the air reach the outer ear, or pinna, which is the part of the ear that's visible. The sound waves then travel from the pinna through the ear canal to the middle ear, which includes the eardrum (a thin layer of tissue) and three tiny bones called ossicles. When the eardrum vibrates, the ossicles amplify these vibrations and carry them to the inner ear.

The inner ear translates the vibrations into electric signals and sends them to the auditory nerve, which connects to the brain. When these nerve impulses reach the brain, they're interpreted as sound.

The Eustachian Tube

To function properly, the middle ear must be at the same pressure as the outside world. This is taken care of by the eustachian tube, a small passage that connects the middle ear to the back of the throat behind the nose.

By letting air reach the middle ear, the eustachian tube equalizes the air pressure in the middle ear to the outside air pressure. (When your ears "pop" while yawning or swallowing, the eustachian tubes are adjusting the air pressure in your middle ears.) The eustachian tube also allows for drainage of mucus from the middle ear into the throat.

Sometimes, the eustachian tube may malfunction. For example, when someone has a cold or an allergy affecting the nasal passages, the eustachian tube may become blocked by congestion in its lining or by mucus within the tube. This blockage will allow fluid to build up within the normally air-filled middle ear. Bacteria or viruses that have entered the middle ear through the eustachian tube can also get trapped in this way. These germs can breed in the trapped fluid, eventually leading to an ear infection.

About Middle Ear Infections

Inflammation in the middle ear area is known as otitis media. When referring to an ear infection, doctors most likely mean "acute otitis media" rather than the common ear infection called swimmer's ear, or otitis externa.

Acute otitis media is the presence of fluid, typically pus, in the middle ear with symptoms of pain, redness of the eardrum, and possible fever.

Other forms of otitis media are either more chronic (fluid is in the middle ear for 6 or more weeks) or the fluid in the middle ear is temporary and not necessarily infected (called otitis media with effusion).