A person’s ears pop when he blows his nose if the action opens the Eustachian tubes that lead from the middle ears to the nose and throat. The tubes help the ears drain fluid and maintain proper air pressure in response to air pressure changes in the external environment.
Eustachian tubes are about 1 1/2 inches long and only a few millimeters wide. They are usually closed to protect the middle ear from undesirable changes in pressure and loud noises, but open when there is movement in the back of the nose and throat.
For one to hear properly, the air pressure inside the middle ear cavity must be the same as the pressure outside. The middle ear can then translate sounds from the environment into vibrations the brain can understand.
The Eustachian tubes therefore open periodically to circulate air throughout the middle ear. This equalizes the air pressure between the middle ear cavity and the back of the throat.
However, swelling from illness, allergies or infections can prevent the Eustachian tubes from opening. Negative pressure may then become trapped. Actions, such as yawning, blowing one’s nose, chewing gum and swallowing repeatedly, can open the tubes momentarily so balance is restored.