Primo, I don't know if I would worry too much about the bacteria in it if you have sealed vials. The reason most people heat it/ bake it is to burn off some of the alcohol that keeps it sterlie. Adding something else oil based also helps dilute it so it takes some of the sting out. Just think of it this way, remember when you got a cut as a kid and the cleaned it with an alcohol pad? Well, now you're just injecting it in you...so that sting you felt on the cut, you're feeling in the muscle. Don't worry though, you learn to love it!!
Ed