This BMJ article studied 117200 women for 36 years and found it increased thr risk if non- hormone related cancers and ovarian cancer. I've not read the whole article to see the how much, and how long yet, just the summary, but it's worth a read.
Hi Londonmumof2 mine was oestrogen positive but I read this information or similar 5 years ago and never dyed my hair again.
I dyed it 1995-2015 and I have absolutely no idea why I bothered because this is it without dye. 
