Separating the outer ear from the middle ear is the eardrum, which vibrates the tiny bones (hammer, anvil, stirrup) in the middle ear. If the eardrum is completely missing from your ear then these bones won’t be able to vibrate as well as they should, causing a permanent hearing loss.
Sometimes the eardrum is there but it’s damaged. You may have heard of a perforated eardrum – that’s when the eardrum has a hole in it. Often these holes will repair themselves. When they don’t they can sometimes be repaired by an operation. But while the eardrum has a hole in it, it may cause a hearing loss – but it’s not always a serious one.
Ear Infections and Glue Ear
Another temporary cause of hearing loss is infection. You’ve probably noticed that when you get a cold you don’t hear so well. That’s because the middle ear fills up with liquid which prevents the hammer, anvil and stirrup from moving properly. The liquid can also push out the eardrum which prevents it from vibrating fully.
Children are especially prone to this form of hearing loss (sometimes called 'glue ear'), and it’s often accompanied by ear-ache due to the intense build up of pressure. Sometimes the eardrum will rupture to relieve the pressure caused by the liquid and this usually eases the pain. The eardrum will repair itself more often than not.
Damage to the Bones
The bones in the middle ear can either crumble, grow more bony or get dislocated (e.g. with a blow to the head). When these tiny bones are functioning correctly, it can make a tremendous difference to our hearing. Without them, a sound may have to be up to 32x louder for us to hear it!
Otosclerosis, for example, can cause the stirrup to become fixed so it can't vibrate in sync with the eardrum. Similarly the muscles that hold the bones in place may become weak. There are operations available that can correct these sorts of damage to the middle ear, but it’s not always practical or possible to perform them.
If they remain damaged, or if they have to be removed, it will result in a hearing loss.
Summary
Although the Middle Ear is a delicately balanced instrument, it is generally very robust with built in mechanisms for keeping itself working correctly. When things do 'malfunction', it is sometimes possible to correct the problem medically or surgically. When this is possible, it can make the difference between a hearing loss being temporary or permanent.
We now move onto the most common cause of permanent hearing loss – damage to the inner ear or to the auditory nerve.