3% is enough to irritate tissue. It sounds wossy but increasing links between irritation and cancer are being discovered. That's what asbestos does. It irritates lung tissue, permanently, and to dumb it way down, you irritate tissue enough times and it says, "fuck you, I'm becoming cancer." The really manly thing to do is trust yourself to have an immune system and not have to kill every germ inside and out of your body. If you keep peroxide up as a habit it sure could lead to cancer. You have a responsibility to not experiment on your body because eventually you are going to fuck up or the long term effects will add up and you will end up with some costly disease or issue at the expense of your family. Do nothing except the clear and obvious. The body is not a fucking playground. If anything that's the lesson that the pharma people need to hear too.