The middle ear that causes discomfort during air travel because it is an air pocket inside the head that is vulnerable to changes in air pressure. Normally, each time (or each second or third time) you swallow, your ears make a little click or popping sound. This occurs because a small bubble of air has entered your middle ear, up from the back of your nose. It passes through the Eustachian tube, a membrane-lined tube about the size of a pencil lead that connects the back of the nose with the middle ear.
The air in the middle ear is constantly being absorbed by its membranous lining and resupplied through the Eustachian tube. In this manner, air pressure on both sides of the eardrum stays about equal. If and when the air pressure is not equal, the ear feels blocked.