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