HAIR COLORING BY MELANIN PRECURSORS 67 COLOR EVALUATION OF HAIR Color values and spectral reflectance data were obtained using the LabScan LS-5100 spectrocolorimeter (Hunter Associates Laboratory, Inc., Reston, VA). Two measure- ments (one of each side) were obtained per tress and averaged. The tress configuration and the design of the hair tress holder allowed for the measurement of the same area of the tress before and after treatment. Results are expressed in terms of the Hunter L, a, and b color scale where L is a measure of lightness and varies from 100 for perfect white to 0 for black. The chromicity di- mensions a and b are color designations, with 'a' being a measure of redness when the value is positive and greenness when negative, while 'b' is a measure of yellowness when positive and blue when negative. In some tables the total color change (TCC) is used. TCC is calculated from the L, a, and b values according to the equation, Tcc = ViL,- L) 2 + (a,- a) 2 + (b,- where subscript i denotes the initial value and subscript f the final value of the color parameters. LIGHTFASTNESS This was evaluated by exposing the tresses in an Atlas Fade-O-Meter (Atlas Electric Device Co., Chicago, IL) equipped with a sunshine carbon arc lamp. The lamp is centrally located in a 19«-inch specimen rack which rotates at approximately three revolutions per minute during the exposure period. An area of 2 cm ) 3.5 cm of each tress was exposed for 10 hours at approximately 65% relative humidity in all light- fading studies. At the conclusion of exposure, the hair tresses were evaluated for color changes. WATER BLEEDING The dyed tresses were immersed in a stirred bath containing 2% of a commercial shampoo (active ingredient, sodium lauryl sarcossinate, 6%) at 50øC for 15 minutes and then thoroughly rinsed under running tap water and air dried. Color measurements were taken before and after the water bleeding test. SHAMPOO STABILITY The colored tresses were hand shampooed with undiluted commercial shampoo (active ingredient, TEA lauryl ether sulfate, 5%) for 30 seconds, rinsed, and towel dried. This cycle was repeated four more times. LabScan readings were taken before and after the shampoo treatment. ACID PERSPIRATION A synthetic perspiration composition was prepared from sodium chloride, lactic acid, histidine hydrochloride, and sodium dihydrogen phosphate, adjusted to pH 3.5 with

68 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS HCI. The colored tresses were immersed for five hours at 50øC in this solution. The change in color depth was determined on the LabScan. HAIR WAVING Commercially available products were used and process instructions followed, with the exception that the hair was treated in straight, rather than in curled, configuration. RESULTS AND DISCUSSION In vivo the formation of melanin takes place within the melanocytes and it is their secretory products (melanosomes) that are responsible for the color of skin and hair. Melanosomes appear as discrete black granules which are injected into the corticular cells located at the base of the hair follicle where the keratinocytes differentiate. From there the melanosomes are carried upward with the flux of the keratin cells. Note in Figure 1 the distribution of the melanosomes throughout the fibrils of the hair cortex. The color of the emerging hair is a complex function of the chemical characteristics and the quantity of the embedded pigment as well as of its particle size. As long as the hair is in the growing phase, the melanin supply continues unimpeded. In the resting phase (telogen) the melanocytes are dormant and resume their activity once the growth (an- agen) phase is reinitiated. The failure of the pigment cell apparatus to produce melanin at this stage manifests itself in hair greying. Figure 1. Longitudinal cross section of brown hair showing melanosomes (black granules, arrow) in the keratin matrix of the hair cortex.