External ear squeeze occurs when your ear canal is blocked by something such as earplugs or earwax. As the water pressure increases while you descend, the air pocket between the obstruction and the tympanic membrane (eardrum) shrinks. This can damage the tissue in the ear canal, usually your eardrum.
Middle ear squeeze occurs when you cannot equalize the pressure in your middle ear. The eustachian tube is a small canal that connects the middle ear to the back part of the nasal cavities and allows pressure to equalize. When there is a problem with the tube, the middle ear volume decreases and pulls the eardrum inward, creating damage and pain. You can try certain maneuvers, called Valsalva maneuvers, such as yawning or trying to blow with your nose and mouth closed, to open the tube and equalize the pressure.
Inner ear barotrauma occurs from the sudden development of pressure differences between the middle and inner ear. This can result from an overly forceful Valsalva maneuver or a very rapid descent. The result is usually ringing in the ear, dizziness, and deafness. This injury is less common than a middle ear squeeze.