Originally Posted by lam2345
I know this is an old thread, but I wanted to add my 2 cents. I remember back in the 80's when it came to light that black hair dye could be dangerous to our health. There are two types of dye to be aware of: the progressively darkening type which contains (contained?) lead acetate and permanent dye. Try googling the following terms (and maybe add the words "hair dye" to get more specific results): 4-methoxy-m-phenylenediamine ; 4-chloro-m-phenylenediamine ; 2,4-toluenediamine These are ingredients in some permanent hair dyes that are reported to penetrate skin and potentially cause health problems. So it's probably as a result of this information that you've heard that black hair dye can be harmful.
As far as dying your hair black goes, I'd personally use a semi-permanent color at least initially. It still lasts for quite a while, up to a month even, but will eventually fade out unlike the permanent dye. :)