There are three kinds of hearing loss that a person can have. One is called neurosensory, or sensory neural, sometimes called nerve hearing loss. Nerve hearing loss is probably a misnomer, because it's rarely the nerve. It's almost always the little hairs inside the organ of hearing that aren't converting the mechanical energy into electrical energy.
The most common cause of an inner ear or neurosensory hearing loss is an age related and genetically determined hearing loss. As we get older we all lose some hearing, and the degree of that hearing loss is very variable. There are individuals in their late fifties or early sixties who have a rather severe loss and need amplification in the form of a hearing aid. And there are others who live into their eighties and nineties that have remarkably good hearing.
Other causes of hearing loss include viral infections, genetic disorders, and, rarely, a benign tumor on the nerve of hearing and balance called an acoustic neuroma. If you have a benign tumor on the nerve of hearing and balance called an acoustic neuroma, you will generally have a hearing loss in only one ear. A hearing loss in one ear should be more alarming to you than in both ears because it brings up the possibility of a tumor such as an acoustic neuroma.
The second type of hearing loss is a mechanical one. We call it a conductive hearing loss because there's a problem with the mechanism that conducts the sound from the outside to the inside. A lump of wax will cause a mechanical hearing loss. A problem with your eardrum will cause a mechanical hearing loss. A problem with the little bones of hearing will cause a mechanical hearing loss. Fluid inside your middle ear will cause a mechanical hearing loss.
The third type of hearing loss is called mixed, a little bit of each.