This pressure difference, if not released, can result in a burst eardrum. This damages hearing, and cold water in the middle ear chills the inner ear, causing vertigo. The pressure difference can also cause damage to other body air spaces, such as the paranasal sinuses. This can also be caused by damaged sinus ducts.
To allow successful equalization, it is important that the diving suit hood does not make an airtight seal over the outside ear hole, and that earplugs are not worn. It is not recommended to dive when a eustachian tube is congested or blocked, e.g. with the common cold, as this may cause what is known as a reverse block ; descent is uninhibited as the valsalva manoeuvre may still clear the eustachian tubes temporarily by force, but during ascent a blockage may stop the air in the middle ear (which is now at depth pressure) from escaping as the diver ascends, which he may have to do as his air supply runs low, and the eardrum bursts outwards, causing the same hazard as with an ordinary burst eardrum, such as cold water in the middle ear deranging the working of the sense organs of balance in the inner ear, causing dizzyness. Divers generally get proper diver training in clearing the ears before being allowed to dive.