Medical or not, you will always hear Etymotics because you don’t use your eardrums for those, they connect straight to your brain.

Medically speaking, I would guess that open backs with absolutely no seal are best as they don't touch your ear canals and allow some ventilation.

Over ears. As long as you don't go over 80db.

Why would ventilation matter, “medically speaking”? Certainly it makes a difference for comfort, I personally much prefer open backs, but I don’t see how it’d matter for hearing damage (volume is everything for that). Maybe it increases the chance of an ear infection, but when has that ever been an issue for IEM users?

If we just focus on hearing damage, it makes sense to think if in terms of which style of headphones you can play the quietest. And advantage there goes to ones that are isolating, because you can listen quieter if you don’t need to drown out outside noise.

Medically speaking ventilation matters because when you live in a hot country like India you tend to sweat a lot. The ventilation helps to keep the sweat at bay and prevent any infections due to excessive sweating.

I can't verify if this is true or not, but in band in high school our instructor told us that in-ear can cause problems because there is very little between the driver and your ear drum.

I'm just relaying what I heard during my education. I'm skeptical of it because I would think what matters most is the SPL at your eardrum, and IEMs often seal and attenuate outside noise, meaning you can enjoy at a lower volume than with open headphones. I can't say I know for certain; my hope is only that this gives you some good ideas for finding real scientific studies.

I guess noise canceling can allow you to play music at a lower volume because your not competing with outside noise as much. From what I've read there's no difference between over ear and in ear as far as hearing loss.

My ass cheeks sweat a lot when I'm doing pelvic thrusts

If you are going for utmost safety over ear is definitely better. I stopped wearing iem’s due to ear infections and I am EXTREMELY hygienic. Depending on the iem the constant ear canal pressure when you insert them is also bad in the long run

Your assumption is correct, at least according to my audiologist. She says it doesn't matter as long as the volume isn't too high, of course iems can also cause infections if not properly cleaned etc.

People sleep with earplugs daily and those push against your ear canals aa well

You're gonna sweat a lot more with open backs vs iems in a hot place