There are several different things that can cause hearing loss. Sound has to get through your ear canal and then go deeper into the eardrum. The eardrum has to vibrate and then the attached hearing bones have to move and vibrate. That causes movement inside the hearing organ, called the cochlea. There are little cells that detect that and trigger a nerve impulse to the brain.
The most common type of hearing loss is where the cochlea that is taking the mechanical sound energy and turning to a nerve impulse has stopped working. That’s what most people who have hearing loss have.That’s the one that’s caused by noise exposure throughout life.
A less common cause is conductive hearing loss, where something is just physically blocking sound transmission from outside the head to inside the head. That’s one that usually we can repair by surgery or medicines.
Then you can have mixed hearing loss, where it’s a combination of both of those two types.
The least common is where there’s a problem with the nerve only, or with the brain itself, where the speech is not getting encoded properly or the brain can’t interpret speech. That would be called an auditory spectrum disorder, but those are extremely rare.