Should I open up paint blisters on car?

Sometimes I see blisters develop on car body which most likely is rust forming. When I see these blisters am I better off to use like a screwdriver to open them up or should I just leave them alone? I usually open them up and apply touch-up paint to it. Are these paint blisters the start of rust forming and how should I best handle them so I can keep my car body looking good?