I have some pretty severe hearing damage on my right ear. The left ear isn’t much better, but at least it’s not as painful. When I get into a loud environment, my right ear will start “crackling” like a speaker lead with a bad connection. “Loud” doesn’t mean “cranked Twin Reverb”...”Loud” means a 3/4-full casual restaurant. ...and I’m never in a completely quiet room, because the constant ringing, humming sound of tinnitus. It’s absolutely wonderful (note sarcasm font)...and it’s absolutely my fault. So, to prevent further damage, I play quieter and I wear earplugs when I play. Sometimes I’ll wear an earplug in my right ear to prevent the “crackle” in the restaurants mentioned above. Side note: I’m an on-site safety coordinator for a construction company. OSHA has a standard (law) that 95dB requires hearing protection for an 8-hour shift, but has issued memos that recommended that earplugs be worn for even sporadic blasts of sound of 90dB or more. 90dB is not very loud—but it’s much quieter than most of us would consider “bedroom/quiet rehearsal” level. As far as the OP’s cited 100dB level is concerned, with some decent earplugs it shouldn’t harm him/her...but as more instruments are added—drums, bass, other guitars, keyboards, vocals, bagpipes, whatever—at a level loud enough to be heard will quickly become a seriously dangerous level, if no hearing protection is worn by the players.