Pressure
The eardrum is the border between the air outside and the middle ear. The middle ear also has air inside it. When the air pressure is not the same on both sides, the eardrum can either be concave or convex.
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How does ear pressure work?
These ear pressure problems might be caused by a number of things like driving up or down a mountain, flying in an airplane or scuba diving. By swallowing yawning you can force the Eustachius tube to open for a moment. This way the air pressure will be equal on both sides again. This also causes the eardrum to move more easily and will probably increase your hearing.