Whether you're flying, scuba diving, climbing a mountain, or even riding in an elevator, air pressure decreases as you go higher and increases as you go lower. If the pressure isn't equalized, the higher air pressure pushes on one side of the eardrum and causes pain.

Children’s ears hurt during a flight primarily because of a physiological struggle to equalize air pressure between the middle ear and the external environment. This occurs most acutely during takeoff and landing when the airplane's cabin pressure changes rapidly. The middle ear is an air-filled pocket connected to the back of the throat by the Eustachian tube. In adults, this tube opens and closes easily to balance pressure. However, in infants and young children, the Eustachian tubes are much smaller, narrower, and positioned more horizontally than in adults, making them far less efficient at clearing pressure blockages. When the plane descends, a vacuum-like effect can pull on the eardrum, causing significant physical pain or a "clogged" sensation. If a child has a cold or allergies, the tubes may be even more swollen, exacerbating the discomfort. This is why experts recommend having children swallow, chew, or suck on a bottle or pacifier during altitude changes, as the muscular action of swallowing helps force the Eustachian tubes open to allow air to pass through and equalize the pressure.