There are two different types of hearing loss.
One is caused by something blocking sounds to the ear, like a buildup of wax, and the other is caused by damage.
The first type is called conductive hearing loss.
My sister had this as a kid due to wax buildup and it was significant.
She wouldn't let my mother or anyone else clean her ears and it progressively got worse.
Finally a trip to the ear doctors resulted in all the buildup wax being removed and she could hear well again.
Other causes include external and middle ear infections and perforated ear drums.
Sensorineural hearing loss is caused by damage, for example to the inner ear of the nerves that conduct sound signals to the brain.
There are several causes of this including tumors, autoimmune disorders, and genetic orders.
More common is noise related and it is preventable.
Exposure to loud noises is what causes it.
Fortunately when I managed rock bands in my 20s and spent lots of time in loud clubs listening to rock music, I wore ear plugs.
Another very common form of sensorineural hearing loss is presbycusis, or age related.
It's also called nerve deafness and typical starts around age forty and gets progressively worse.
It has a genetic component which means in runs in families.
Unfortunately both my uncle and mother have it, my uncle quite badly, so I may as well.
There is no cure for presbycusis, or age related hearing loss, although there are potential "fixes" like hearing aids.