Such an eardrum cannot vibrate naturally, so hearing sounds muffled or blocked. Also, the stretching of the eardrum can be painful. This is because the membranes that line the Eustachian tube are similar to and continuous with nasal membranes. Consequently, a stuffy nose leads to stuffy ears because the swollen membranes block the opening of the Eustachian tube. Another cause of blocked Eustachian tubes is infection of the middle ear which creates swollen membranes.
Children are especially vulnerable to blockages as their Eustachian tubes are narrower than adults.
Air travel is sometimes associated with rapid changes in air pressure. To maintain comfort, the Eustachian tube must function properly, that is, open frequently and widely enough to equalize the changes in air pressure. This is especially true when the airplane is coming down for a landing, going from low atmospheric pressure down closer to earth where the air pressure is higher. In the early days of airplanes with open cabins and cockpits, this was a major problem to flyers. Today's aircraft are pressurized so that air pressure changes are minimized.