Yes you can absolutely dye your hair when breastfeeding. There is no evidence that dying hair affects breastfeeding! Only that baby might not like the smell :) this is a myth! https://sg.theasianparent.com/dye-hair-while-breastfeeding/?utm_source=search&utm_medium=app
Why not? The chemicals from the dye won’t go to your bloodstream or even your breastmilk. Is the nutrients from the food that you take that matters.