The Eustachian tube plays a crucial role in regulating air pressure in the ear. When it becomes blocked, usually due to swelling from a cold, the air pressure in the ear changes, leading to the sensation of a plugged ear. This condition can also affect hearing temporarily and may cause a feeling of fullness or pressure in the ear. Understanding the anatomy and function of the Eustachian tube is essential to comprehending why colds can lead to ear blockages.