How do you know if the reduction of hearing in one ear is temporary?

I’ve had some experiences with hearing loss over the years. Long term noise can be a cause. Going to rock concerts for instance can impact your hearing pretty severely in the short term but can mostly clear up even though there is still long term damage. I have a child that had hearing problems when young that we eventually found was caused by wax build up in the ears. Some ear infections can cause temporary hearing loss.
When a child starts complaining about hearing loss, you need to think and have them think about what was happening in the recent past. Loud noises? Ear Buds? things like that can all contribute. Take a look inside the ear. You can get one of those tools the doctors use at your local CVS for a few bucks. Take a look and see if there is a lot of wax or a red/swollen look. And if you can’t find anything else, take them to the doctor. If the doctor determines it is short term, ask them how they determine that and if it is something you can check at home.

Get an examination by a doctor. Perhaps you have a lot of wax in that one ear, and all you need is a good cleaning, which the doctor can do easily.

See an E.N.T. (Ear, Nose and Throat) doctor.

@seawulf575 Thanks, that was helpful. I went here:
https://www.webmd.com/cold-and-flu/ear-infection/check-child-ear-infection#1
as well as here:
https://www.mayoclinic.org/diseases-conditions/ear-infections/symptoms-causes/syc-20351616
The case I’m referring to has none of the symptoms listed there. Maybe some itchiness sometimes.
@kritiper I don’t think you read the whole question.

@flo Speaking from experience, dearie…