Hearing loss is a complex subject. Usually people mean the loss of being able to hear high frequency sine waves. Because that is what they notice and that is what they test. On average people start losing this pretty early on and it only gets worse with age.
Had a guy here couple weeks ago when I played a sweep tone, as the highest frequencies faded out for me he was covering his ears saying stop the pain! I could hear nothing. This made me think maybe my super-tweeters were set too high. Because I can't hear that high, so how could I know? But then playing music he was just fine. So this whole subject is very complicated.
At the same time, this same guy who by definition has better hearing than I do was unable to hear a whole bunch of things that were easy for me to spot. So there is hearing, which is more physical, and there is listening, which is more intellectual.
Then there's things like tinnitus, which also tends to get worse with age but can also be made worse by long exposure to high sound levels. I don't see how headphones or earphones can be any better or worse than the same volume level with speakers. If you listen louder with headphones blame the volume not the headphones.
But tinnitus can also be caused by other things. Take a handful of aspirin some time, give yourself tinnitus. It will go away. Other similar drugs can over time cause it as well. Then you get into a whole big long list of possible causes and remedies.
For lawn mowing I use ear plugs and over the ear protection. But then even this gets complicated. It is not just volume but exposure time that leads to hearing loss. The noise level driving a lot of cars isn't that loud, but it is real steady and continuous and will damage just as effectively over time as firing off a 45 once a week. But nobody wants to hear that.
So I pretty much quit worrying about it. Except for the lawn mower. I'll keep doing that.