How your ears unblock

The middle ear is an air-filled cavity behind the eardrum, and it is not completely sealed off: a channel called the Eustachian tube connects it to the throat. Its job is to keep the air inside at the same pressure as the air outside, because the nasopharynx, the upper part of the throat, is open to the outside.

The tube does not stay open. It opens for brief moments, when you yawn, when you swallow or when you sneeze, because at those moments two palate muscles contract, the levator veli palatini and the tensor veli palatini. It is like a small window that opens for a second and leaves the two pressures even.

That matters when the pressure outside rises, which is what happens as a plane descends or as you go down while diving. When ambient pressure rises, the air trapped in the middle ear takes up less space and leaves something like a vacuum that has to be filled.

And the two directions are not the same. On the way up, pressure equalizes on its own; on the way down, an active maneuver is needed. If that does not work, negative pressure stays inside, and that is what you feel as a blocked ear.