If you are using a permanent hair color you have to lift the hair using hydrogen peroxide (developer). This process raises or opens up the cuticle layer of the hair to allow the color molecules to penetrate the cortex depositing the color which could damage the hair if not done properly. If you use the wrong level of peroxide or if you constantly change your hair color (over-processing), this is what will cause damage to your hair. However, if you use a semi-permanent or demi-permanent they will help add extra shine and condition to the hair but will only last a couple of shampoos.