Why is frequent equalization essential during descent?

Frequent equalization during descent is essential primarily to prevent ear pain and injury from pressure changes. As a diver descends, the pressure around them increases, which can create a difference in pressure between the outer ear and the inner ear. If this pressure difference is not equalized, it can lead to discomfort, pain, and even potential injury to the eardrum and other structures of the ear.

The process of equalization involves using techniques, such as the Valsalva maneuver or Toynbee maneuver, to equalize the pressure in the middle ear with the external water pressure. This action helps to maintain comfort and ensures that the diver can continue the descent safely. If equalization is not performed frequently and effectively, it can lead to barotrauma, which is a serious condition resulting from the inability to equalize pressure.

Other options may have their relevance in different diving contexts, but preventing ear pain and injury is the primary concern when it comes to the effects of pressure changes during descent.