The eustachian tubes run between the inside of the ears and the back of the throat. When a person swallows, the eustachian tube opens briefly to match the air pressure in the middle ear with the air pressure outside the ear.
If the eustachian tubes become blocked, pressure changes cause pain in the ear. Fluid may build up in the ear, sometimes leading to infection (otitis media). Young children are at an increased risk for ear infections because they have eustachian tubes that are shorter, more horizontal, and more easily blocked than those in older children and adults.
WebMD Medical Reference from Healthwise