no, H202 does not kill good bacteria because good bacteria are oxygen breathing. They are not killed by the release of oxygen. It only kills bad bacteria.. As for the whiteness and sensativity in your gums- you definitely have oral thrush (yeast infection) in your mouth and its quite severe from what you have described. I would cut back on the h2o2 treatments, but don't brush with the h2o2, just do a mouth swish with the 3% every day or maybe a few times a day. The tissue in your gums is too sensitive right now from the thrush and the brushing is aggravating it. Using the h2o2 by itself will make the gums stronger and healthier over a period of time you will notice that they just look healthier and feel more firm. I would also recommend right now doing a Sea Salt mouth swish to help disinfect and heal the soreness in your mouth.. this is also really great for your gums too. Also you may wanna look into a natural bristle toothbrush that has soft bristles.