Before we go into how to bleach your hair at home, we should offer some words of caution. First and foremost: using chemicals can be dangerous in and of itself. Secondly, every time you apply bleach you are damaging your hair, period. For that reason, you should not bleach your hair if the follicles are already dry, coarse, or damaged. And if you recently coloured or processed your hair, wait at least three months before bleaching it.