The eustachian tube is a canal that connects the middle ear to the nasopharynx, which consists of the upper throat and the back of the nasal cavity. It controls the pressure within the middle ear, making it equal with the air pressure outside the body.

Most of the time the eustachian tube is closed, opening only during activities such as yawning, swallowing, and chewing, to allow air through the passage between the middle ear and nasopharynx. When atmospheric pressure changes rapidly, causing a sudden feeling of blockage in the ear (such as during airplane travel), these activities can be done on purpose to open the tube and equalize the pressure within the middle ear.

When the eustachian tube will not open enough to equalize pressure, symptoms such as discomfort, dizziness, or ringing in the ear may result. Visual examination of the eardrum with a lighted scope helps to determine if the cause is inflammation, swelling, or fluid in the ear. Conditions such as nasal congestion, infection of the ear or sinus, or allergies may cause these symptoms and lead to eustachian tube problems. These causes can often be treated with decongestant medication or antibiotics, but in severe cases, surgery may be necessary.