Ears Popping

When you travel slowly up a mountain, your hearing gets slowly worse and worse and pain develops in your ears. This can be stopped by yawning, chewing gum or swallowing (or perhaps some other way).

When you yawn, you hear a pop, the pain lessens and your hearing returns to normal. The questions to be answered are, what causes the pain and loss of hearing and how, exactly, are you fixing the problem?

To answer these questions, we need to know a little biology – specifically the structure of the ear.

Image from ScienceLearning.org.nz (University of Walkato)

In the image above, the most important parts (for chemists) are the ear canal, the ear drum and the Eustachian tube. Here's how it all relates to a person's head.

The ear canal is just the air filled space between the outside world and the ear drum. Because this area is open, the pressure here is always the same as the atmospheric pressure.

The ear drum is a small flap of skin that separates the air around you from the inside of your head. Vibrations of this flap are transferred to the hammer, anvil and stirrup...(never mind, that's biology).

The Eustachian tube is an air filled tube that runs from behind the ear drum to the back of your throat. The bottom of the tube is generally closed (after all, you don't want to get cheese doodles up there), but can be opened when you stretch the back of your mouth. Because this tube is sealed (always at the ear drum and usually in your throat) the pressure is not necessarily the same as the atmosphere. More correctly, the pressure in the tube is whatever the pressure was in the atmosphere the last time the tube was opened.

Under normal circumstances, the pressure inside the Eustachian tube and the pressure of the atmosphere around you are the same. As a result the force on either side of the ear drum is even and the ear drum is straight.

However, if you drive up a mountain, the air pressure around you gets lower (less air piled on top of you). This means that the forces on the ear drum are no longer equal and, as a result, the ear drum is bent and stretched. This makes it harder for it to vibrate (interferes with hearing) and it stretches the nerves (it hurts).

If you then open the bottom of the Eustachian tube (by yawning, chewing gum, swallowing, etc.) the air will push out of the tube (since the pressure inside is higher) until the pressure in the tube and outside the tube are equal. This will allow the ear drum to “pop” back into it's normal shape, the pain goes away and it can now vibrate normally (your hearing comes back).

When you drive back down the mountain, the pressure around you increases (more and more air on top of you) while the pressure inside the Eustachian tube stays at the lower pressure from the top of the mountain. Since the pressures are again unequal, the ear drum will again be stretched (only this time it is pushed in rather than out). Yawning, etc., will open the tube and the higher pressure atmospheric air will be pushed into the Eustachian tube, until the pressures are again equal.