A: There is little information about colouring your hair while breastfeeding, however it is unlikely that it would cause much or any damage, similar to colouring while pregnant. The NHS website states: “Information about hair treatments while breastfeeding is limited. However, it's known that very little of the chemicals used in hair dye actually enter your bloodstream. This makes it very unlikely that a significant amount will be passed on through your breast milk. In the past, many women have used hair treatments while breastfeeding with no known negative results.”