Hair Coloring 150 The levels of copper and iron are generally very low in tap water ( 1 ppm) as compared to the water hardness ions, calcium and magnesium (20–400 ppm) and thus the final levels in hair are also much lower. The levels of copper and iron in hair are typically in the range 20–200 ppm vs. a range of 3,000–10,000 ppm for calcium and magnesium. However, these metals are important because they can react catalytically with hydrogen peroxide during the coloring process to form hydroxyl radicals. These radicals are highly reactive and will cause cystine oxidation as well as peptide degradation. The changes to the hair structure will occur preferentially in the cuticle where the metals are located. This type of damage to the cuticle protein structure leads to increased cuticle loss during brushing and combing. Free radical damage is also thought to be a key cause of hair structure changes by persulfate bleach products. Damage reduction technologies of consumersOne strategy to reduce the ability to observe the effects of hair structure changes caused by hair coloring is to use an after dye conditioner. Conditioning agents such as silicone polymers or polyquaternium polymers deposit on the hair surface to increase the hydrophobicity and thus improve hair feel. These conditioners are not preventing the damage but rather masking the changes and also protecting hair against the damaging effects caused by combing and brushing. Increased hydrophilicity of the hair surface caused by the F-Layer removal and cysteic acid formation also has the consequence of changing the deposition profile of conditioning agents onto the hair. Silicones, which are important conditioning materials used in both shampoo and conditioner products, will have a significantly reduced deposition profile on colored hair vs. uncolored hair. This has recently led to a variety of products that have been formulated especially for use by consumers with colored hair. In some cases, the silicones are modified to improve their deposition profile36 or the surface of the hair is modified to reduce the hydrophilicity and in that way increase silicone deposition.37 Higher silicone deposition