My old school friend, Christopher, read my previous posting about herceptin and hair tinting and sent this response to me via facebook. I find it so fascinating htat have decided to repost it here. Oh and by the way, he is a professor of chemistry I think it is (cannot remember now) in the US. Either way, he is someone I respect and trust:
Saw your "From Under my Hat" musings about use of tints / dyes / colourants. I would side with your former head nurse, and encourage you to wait. The chemicals in these processes (those needed to facilitate penetration of the colouring agent, as well as the colouring agents themselves) are rough on living cells. Anything that can promote penetration into hair will promote penetration into cells. Also, anything that gets into the hair can travel along it on the inside and reach the root. The dividing cells in the root already took a pummeling from the anti-cancer drugs, so it would be best to pamper to them for a while.