Ears 101: What Causes Ear Infections?

A depiction of the difference between a normal and infected ear. (Source: http://www.drugs.com/health-guide/middle-ear-infection-otitis-media.html)

A drawing showing the difference between a normal and infected ear. (Source: http://www.drugs.com/health-guide/middle-ear-infection-otitis-media.html)

Ear infections are very common in childhood. In fact, the National Institute on Deafness and Other Communication Disorders (NIDCD) estimates three out of four children will have at least one ear infection by the age of three. In our last Ears 101 post we talked about what an ear infection is and the different types. Now I bet you’re wondering, “What causes an ear infection?”

Ear infections develop when the Eustachian tube becomes swollen or blocked, inhibiting its ability to properly drain fluid from the middle ear. The Eustachian tube can become blocked because of swelling or congestion due to an upper respiratory infection, a common cold, allergies, or even irritants like cigarette smoke.

If the Eustachian tube is blocked, fluid can accumulate in the middle ear, creating a warm, moist environment that is perfect for any present bacteria to start to multiply. This is sufficient to produce an ear infection on its own. To make matter worse, negative pressure created by a blocked Eustachian tube can also lead to direct extension of infectious agents from the nose and throat to the middle ear.

There are two primary culprits in ear infections: bacteria and viruses. The majority of ear infections are bacterial, however viruses play a complex role in the ear infection story. Some viruses can create the conditions that lead to bacterial ear infections by creating inflammation, blockage and fluid build up in the Eustachian tube, which allow bacteria to proliferate.

Ear infections are more common in children than adults because their Eustachian tubes are shorter, narrower and positioned horizontally which makes draining fluid more difficult. As children get older, the angle increases, thus children sometimes “grow out of” ear infections.

Many thanks to Dr. Sloane Sevran, a Pediatrician in Encino, CA, for her editing contributions on this post. Have any ear questions you’d like to see answered on the blog? Post them in the comments section.

Disclaimer: This information is meant for educational purposes only; none of the above information should be viewed as medical advice, diagnosis or treatment.

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