If you google it you'll find different things. I just did cos ive heard of long term use of hair dyes might be linked to cancer. Here's something I found-
dyes that are intended to "stay put" contain materials that actually penetrate the hair shaft. They can in some cases add minerals such as lead (black dyes), manganese (brown dyes) and copper (red dyes)
for the long term, we have very recently learned from the london hazards centre that permanent dyes can enter the bloodstream from the scalp, and can be found in the urine 40 minutes after the hair is dyed. Recent research has linked them to bladder cancer; over 4,000 women a year are known to suffer from balder cancer, and 1,600 deaths are caused by it, with a high number of hair-dressers being included in these.
Because the dye enters the blood, we advise people very strongly to avoid hair dyes while the ova is ripening, and during pregnancy and breast-feeding. It is really only sensible to keep from all avoidable causes of cancer once you are a mother - and obviously, if you decide not to dye, it will be doing your hair-dresser a good turn too!
The wash-in/wash-out dyes appear at the moment to be less suspect, but we have insufficient research on them to be able to give total reassurance. We will try and give further updates in forthcoming foresight newsletters.
Foresight association
april, 2004
so it can get in your bloodstream through the actual hair not the skin?