Chemical hair treatments like coloring and highlights are generally considered safe while breastfeeding, provided you ensure proper ventilation to avoid inhaling fumes. For extra precaution, many mothers prefer to feed or pump before the appointment to avoid being away from their baby while the chemicals are on their scalp. Formal treatments like keratin or straightening may involve formaldehyde gas, which requires extra caution; if you choose to proceed, look for 'zero-formaldehyde' options (like nanokeratin) and verify ingredients with your doctor.