J. Cosmet. Sci., 58, 495-503 (September/October 2007) Hair coloring systems delivering color with reduced fiber damage JENNIFER M. MARSH, JANINE FLOOD, DIRK DOMASCHKO, and NIRANJAN RAMJI, The Procter & Gamble Company, Whitehall Lane, Surrey, UK, TW20 9NW U.M.M.), The Procter & Gamble Company, 11810 East Miami River Road, Cincinnati, OH, 45252 U.F., D.D.), and The Procter & Gamble Company, 8700 Mason Montgomery Road, Mason, OH 45040 (N.R.). Accepted for publication May 22, 2007. Data presented at the Annual Scientific Meeting of the Society of Cosmetic Chemists, New York, December 2006. Synopsis The possible metal-induced formation of free radical species such as the hydroxyl radical (HO*) during the use of permanent hair coloring products has been demonstrated. These highly reactive species are formed from the reaction of hydrogen peroxide with redox metals such as copper, which are thought to be absorbed by the hair from the from-the-tap wash water. Formation of such radical species has been shown to lead to measurable keratin fiber damage. The incorporation of chelants such as N,N' -ethylenediamine disuccinic acid (EDDS) has been demonstrated to prevent this metal-induced radical formation and thus significantly reduce the fiber damage. This chelant is highly effective due to its ability to specifically bind low levels of copper in the presence of relatively high levels of calcium, as is found in hair. INTRODUCTION The use of permanent hair colorants is widespread and allows consumers to either change their natural hair color and/or cover gray. However, there are trade-offs that the con­ sumer has to make if she or he is using these products on a regular basis. One of the main trade-offs is the fiber damage that is sometimes seen after multiple use (1). This can lead to the consumer's experiencing poor hair feel, an increased incidence of split ends, and generally hair that loses some of its healthy appearance and shine. Thus developing hair coloring systems that allow the consumer to color on a more regular basis and yet maintain hair quality is highly desirable. There are two key chemical processes that take place during the coloring process that contribute to final color. The first is the oxidation of the melanin pigment and previ­ ously deposited dyes that lightens the underlying hair color, and the second is the oxidation of the dye precursors to form the colored chromophores (2,3). For both processes the oxidant is essential, and in the majority of retail hair colorants the oxidant 495

JOURNAL OF COSMETIC SCIENCE used is a combination of hydrogen peroxide and an ammonia alkalizer at a final mixed pH of 10. Importantly, it is also the oxidant that is mainly responsible for the damage to the hair fiber that can lead to the loss of the hair's strength and healthy appearance. The key chemical species that is reported in the literature (4) as responsible for both the lightening and damaging processes of keratin fibers is the perhydroxyl anion. This species is present at pH 10 and above, from the deprotonation of the hydrogen peroxide (equation 1). However, it is also well known in the literature (5) that hydrogen peroxide at high pH is likely to form reactive radical species that would be an alternative source of fiber damage. Hydrogen peroxide can readily decompose in the presence of redox metal ions such as copper and iron to form hydroxyl and perhydroxyl radicals, HO* (equations 2-4). The hydroxyl radical is extremely reactive toward organic substrates, with typical reaction rates being diffusion controlled (k = 109 M- 1 s- 1 ) (6), and would be expected to react with hair if formed. In addition, molecular oxygen can be formed from the decomposition of these radical species (equation 4). It should also be noted that the chemistry is catalytic, i.e., only a small amount of redox metal is required for extensive decomposition of the hydrogen peroxide to occur. H202 � H++ HOO- pKa = 11.6 H202 + Cu2+ ➔ Cu+ + HOO* + H+ H20 2 +Cu+ ➔ Cu2+ + HO- + HO* HOO*+ Cu2+ ➔Cu+ + H+ + 0 2 (1) (2) (3) (4) The objective of this study was to investigate whether free radical generation is present during the coloring process and to measure whether it is a significant contributor to hair fiber damage. A strategy of using chelating agents to prevent this radical chemistry was also investigated. EXPERIMENTAL RADICAL FORMATION MEASUREMENTS Caucasian untreated mixed hair (medium brown), obtained from a commercial source (IHIP, New York), was formed into swatches (16 cm, 1.5 g). The hair swatches were subjected to five repeat coloring cycles with a commercial blonde permanent hair col­ orant. Between each cycle the hair was washed twelve times in tap water with a commercial clarifying shampoo. The hardness of the tap water was 275-300 ppm calcium ions and 0.1-0.2 ppm copper ions. Metal analyses were carried out using inductively coupled plasma mass spectroscopy (ICP-MS) by AES (Newcastle, UK). The chemiluminescence measurements were carried out on an L-Max microtiter plate luminometer from Molecular Devices, using the Revelations software package. The instrument was set up in the Long Kinetic mode, the kinetic time interval of measure­ ment was 2.50 min, the total run time was 1000 sec, and the temperature was ambient (auto gain setting). The blank, test, and control set locations were specified on the plate. The area under the curve was calculated by the software used for data analysis. Each test was a replicate of five sets. All test and control readings were blank subtracted. The materials used were Tris buffer saline (pH 7) supplied by Fluka, hydrogen peroxide