JOURNAL OF COSMETIC SCIENCE 6 quick dye loss in the early stages is the high pH in the dyed hair fi ber. Dyeing hair results in a large increase in pH to ~9. A 2-min rinsing step after the hair dyeing procedure is not suffi cient enough to lower the pH of hair to 6.5. Under high pH conditions, the cu- ticles are swelled and therefore provide open channels and pathways for dye to leach out of the fi bers. It should be noted that most contemporary hair dye systems contain a con- ditioning step to bring the pH down closer to physiological conditions. To probe dye spatial distribution inside the hair, dye species were imaged across hair sections by FT-IR spectroscopic imaging. Figure 2 presents the relative dye concentra- tion across hair sections. The image was generated by integration ratio of the peak at 1116 cm-1 resulting from the dye species to the amide I peak at 1650 cm-1 due to hair proteins. Such an analysis indicates that the cuticle region has higher dye concentrations than the cortex. Free dyes/residues were also visualized in the cuticle areas of the freshly dyed hair fi ber surface (Figure 3) with an optical microscope. Studies have shown that the preferred route of reagents to enter the hair fi ber is the scale edge between cuticle cells, either through the cell membrane complex or endocuticle (11). During the dyeing process, dye molecules aggregate in the cuticle area as reagents perme- ate into the hair fi ber. Therefore, the cuticle area is exposed to and contains a higher amount of dye molecules than other areas of the hair fi ber. These results explain our ob- servations from the kinetics measurements, which indicate that dye leaching is much faster in the early stages immediately after dye deposition. Much of the initial dye fading results from dye loss from the cuticle structure, which is dissolved once the dyed hair fi ber comes in contact with water. Previous work in this area demonstrated that, in addition to the cortex, reactions between the dyes and developer also occur at the surface of hair and in the cuticle (12). In addition, studies by Chandrashekara and Ranganathaiah revealed that dyes diffuse much more quickly into the cuticle than they do into the cortex (13). Therefore, it should stand to reason that since a signifi cant quantity of dyes are located in the cuticle structure, these are likely to diffuse from the hair structure fi rst. As already noted, most contemporary hair dye protocols involve rinsing, shampooing, and conditioning steps to bring the pH of hair down closer to physiological conditions Figure 2. FT-IR image of dye distribution in hair fi ber cross sections. The image was generated by taking the ratio of the integration of the peak at 1116 cm-1 resulting from the dye species to the amide I peak at 1650 cm-1 resulting from hair proteins.

HAIR DAMAGE DURING MULTIPLE OXIDATIVE DYEING AND SHAMPOOING 7 with the aim to “close” the cuticle and, of course, prevent the leaching of dyes from the interior of the fi ber. Shampooing plays a major role in the color fastness of hair. In the experiments conducted in this study only the infl uence of water on hair dye leaching is considered. It is very likely that results may be different in presence of surfactants. Dye leaching from dark brown hair is generally faster than from white hair. This trend is more obvious in the later stages of dye leaching kinetics, which refl ects that dye mole- cules are transported from the cortex region through the cuticle, and then to the solution. More than likely, more pores and channels are created in the dark brown hair during the dyeing process when melanin granules are dissolved. This would provide extra pathways for dye molecules to leach out. These results are in agreement with previous studies that demonstrated that hair color fading is greater in pigmented than nonpigmented hair when exposed to solar radiation in combination with shampooing cycles (14). INVESTIGATION OF HAIR DAMAGE AND HAIR DYE LOSS DURING MULTIPLE OXIDATIVE DYEING–LEACHING CYCLES The hair surface becomes more hydrophilic during the dyeing process. The dyeing proce- dure removes most lipids from the hair surface since it is generally performed under alka- line conditions. After the fi rst cycle of the dyeing–leaching process, the contact angle of hair decreases from 104° for virgin hair to 84° for dyed-leached hair. There is no visible damage in the internal structure from AFM observations after the fi rst dyeing–leaching cycle alone. However, if a prebleach process is conducted prior to the hair dyeing process, Figure 3. A photomicrograph of the freshly dyed hair surface of dark brown hair obtained by refl ectance light microscopy (scale bar: 10 microns).