REDUCED HAIR DAMAGE FROM COLORING SYSTEMS 499 Table II RRFP Results for Untreated vs Colored Hair Untreated hair Colored hair RRFP 0 89 Figure 1. Gas formation after 2 minutes (left) and 3 5 minutes (right). the hypothesis that redox metal-initiated radical formation is occurring during the coloring process. RADICAL DAMAGE TO HAIR The data described in the previous section indicate that copper ions and water hardness ions are present in consumer hair and that similar levels of these metals can also be found on substrates prepared in the laboratory. It was shown that these levels of copper can cause redox metal-activated radical formation to occur, producing hydroxyl radicals and gas generation. A set of experiments was designed to show whether this radical formation can lead to fiber damage. Untreated hair was subjected to five repeat coloring treatments with a commercial level 3 permanent blonde colorant product. In-between each coloring cycle the hair was washed with water, wherein the flow rate, metal ion content, and tem­ perature were closely controlled and monitored. Half of the hair was washed in water containing 150 ppm of water hardness ions (calcium and magnesium in a 3: 1 ratio) and 1 ppm of copper ions. The other half of the hair was washed in water containing the same 150 ppm of water hardness ions but no copper ions. After each cycle the hair was assessed for formation of surface cysteic acid using an FT-IR (Fourier transform infrared) method that has been established to be suitable for studying the effects of oxidative treatments on hair (10-12). Figure 2 sets out the FT-IR cysteic acid measures for the hair washed in tap water containing copper vs the hair washed in tap water containing no copper as a function of the number of washing cycles. These data show that the presence of copper in the water significantly increases the formation of cysteic acid, implying that metal-induced radical chemistry is taking place

500 JOURNAL OF COSMETIC SCIENCE 120 100 80 ::::, u 60 a: 40 20 0 0 2 3 4 5 6 Cycle Number Figure 2. FT-IR cysteic acid formation in the presence vs absence of copper ions in water. on or near the fiber surface. It is hypothesized that as the level of cysteic acid increases, the additional sulfonate groups act as further sites to complex metal ions including copper. Thus, there is a synergy in that as the level of colorant damage increases, so too does the capacity of the fibers to take up copper, leading to even further metal-induced radical damage. In addition, the cuticle appearance of the fibers after the five repeat coloring cycles plus washing was assessed via SEM (scanning electron microscopy). Significantly more cuticle damage was observed on the hair that had been washed with tap water containing copper ions (see Figure 3). This high level of cuticle damage is not unexpected if hydroxyl radicals are being formed. This species is highly reactive and not selective it would be expected to not only break cystine disulfide bonds but also to react with other species such as peptide bonds critical to the integrity of the cuticle structure. PREVENTION OF RADICAL DAMAGE One strategy to prevent the formation of hydroxyl radicals from the reaction of redox metals with hydrogen peroxide is to introduce an effective chelant. A chelant is defined Figure 3. Left: hair washed in tap water (no copper). Right: hair washed in tap water (1 ppm copper).