I recently helped my bonus-sister to dye her hair, I read all parts of the instructions and it had the usual warning that you shouldn't use it straight away but rather put some on your skin and leave it there for 48 hours to make sure you werent allergic to it and that you should do before each use. Does anybody really do that? Every time? We are both allergics but we are also all about instant gratification and have never bothered with it. I think it's quite possible for somebody to tolerate it just fine for the amount of time it takes to dye the hair, but not having it on the skin for 48 hours.
I also remember that it used to advise you to first dye just some strands of your hair to see how it turned out, I never bothered with that, have you followed that advice when dyeing your hair at home?