La Leche League's new Breastfeeding Answer Book addresses this issue on
p. 382:

"No evidence exists that nursing mother's use of hair care products, such
as hair dyes and permanents, has any effect on her breastfeeding baby.
When a mother uses hair-care products, some of the chemicals will be
absorbed through her skin.  If her scalp is healthy and intact, less will
be absorbed than if the skin on ther scalp is scratched or abraded."

HTH!

Karen Zeretzke, MEd, IBCLC
Baton Rouge, Louisiana