Ear Infections are Caused by a Build-up of Fluid in the Middle Ear

Ear infections are caused by a build-up of fluid in the middle ear.

According to the Mayo Clinic, the middle ear is a pea-sized chamber behind your eardrum (tympanic membrane) — a small circle of tissue that vibrates in response to sounds. It contains three tiny bones (ossicles) that send vibrations from your eardrum to your inner ear, where they're converted into the nerve impulses representing sound. These impulses are what allow you to hear.

Your middle ear is connected to the back of your nose and your throat by a narrow passageway called the eustachian tube. Normally, this tube helps equalize the pressure inside and outside your ear. It also helps drain fluids from your middle ear.

Most ear infections begin with an upper respiratory infection, such as a cold, which can cause swelling and inflammation in the eustachian tubes. If the inflammation blocks the tubes completely, it can trap fluid in the middle ear. Middle ear fluid is an ideal environment for the growth of bacteria and viruses that cause the actual ear infection.