Your ears pop in air planes because the air high above the surface of Earth is less dense than air near the surface, because air near the surface has all the air above it pushing down.
Some air planes can fly so high they require oxygen masks or a pressurized cabin, so the pilot and passengers dont pass out for lack of air. Even higher and air planes cant fly because their wings require air to provide lift.
As you ascend in an airplane and the air pressure decreases, the air trapped in your inner ear will cause your eardrums to push outward. This expansion causes not only the discomfort you feel before your ears "pop," but also a decrease in hearing ability, because the pressure on your ears drums makes the sound harder to transmit.
Your body can equalize the pressure between your inner ear and the atmosphere by allowing some air from your inner ear to escape through the Eustachian tubes, two small channels that connect the inner ears to the throat, one on each side.
When they open, you feel the pressure release and you hear the change because its happening in your ear. This equalization of pressure is the "pop."
On the way down from an air plane flight, the air pressure increases, while your inner ear is still at the lower pressure it has adjusted to. Now, the extra pressure pushes the eardrums inward.
Eventually, the pressure will equalize again, but many people dont wait, they just hold their nose closed, close their mouth and blow. Because the air from their lungs has nowhere to go, it is forced into the inner ear through the Eustachian tubes, "popping" their ears.
This effect can happen to people driving through the mountainous areas or riding elevators in tall buildings, but it is more noticeable on airplanes because the altitude changes quickly and they fly higher than buildings or mountains.
T. McWilliams and Dr. J. Bass contributed to this report
