Eustachian tubes are small tube-shaped passageways on either side of the head. They connect the back of the throat, or the pharynx, to the middle ear. Sometimes eustachian tubes are referred to as pharyngotympanic tubes, but the term eustachian is still more common and recognizable by those without a medical background.

The term Eustachian tubes arises in honor of the scientist, Bartolomeo Eustachius. He studied the ear in the 16th century and defined its components with greater precision than had been accomplished in the past. He clearly dissected human bodies and feared excommunication for doing so since the Catholic Church did not permit this.

Among other things Eustachius and scientists have discovered since his time, is that the eustachian tubes are about 1.5 inches (3.81 cm) long in adults. One of their more interesting features is that often the eustachian tubes remain closed. However, they may open to keep pressure values consistent between the middle ear and the throat.

This opening of the eustachian tubes, in an airplane setting creates a small popping noise. Most people are fairly familiar with this noise if they travel by air, or climb tall mountains. The pop of the eustachian tubes can bring relief as pressure built up in the middle ear can become uncomfortable.

In order to force this opening in the eustachian tubes people often chew gum or try to yawn. Yawning does tend to open the eustachian tubes, as does opening the mouth wide. It stretches the muscles in the neck allowing the tubes to open up. The tubes also open slightly during colds and allergies to drain mucus from the ears into the pharynx. However, if the mucus hardens or the eustachian tubes become swollen, fluid cannot drain properly, and may accumulate and grow bacteria in the middle ear, causing ear infections.

One of the reasons that children are more prone to ear infections is because the eustachian tubes are shorter and also are more horizontal to the nose and throat. In adult ears, the eustachian tubes normally point downward toward the throat, which allows for easier drainage, since simple gravity does some of the work. The horizontal position of the eustachian tubes in children means that there is very little downward flow into the throat. This can cause a back up of mucus and thus middle ear infections.

In some instances, the failure for the eustachian tubes to properly drain causes ear infections with such frequency in children that they have tubes placed in their ears to keep the passageway from the eustachian tubes to the throat open. This allows for easier drainage and frequently ends bouts of ear infection. As a child ages, the tubes tend to fall out because the passageway to the throat has been naturally widened.