50 JOURNAL OF COSMETIC SCIENCE Case 2: Irradiation without washing. The hair tresses remained unwashed throughout. The color was measured at identical irradiation times to those in Case 1. IRRADIATION OF GRANULES OBTAINED FROM RED HAIR In order to accurately measure the color, granules were fixed in a silicone film using the following method: Granules (40 mg) were dispersed in hexane (3g)/dimethypolysiloxane (Silicone SH-200C, 1,000,000 cs Toray Dow Corning Silicone, Tokyo, Japan) (0.6 g), after which 0.2 g of the dispersion was poured into a petri dish (I 16 mm) and left overnight to remove all the hexane and leave the granules in the silicone film. Nine samples were prepared. Three of the samples were kept shielded from light, three addi­ tional samples were irradiated with VIS light, and the final three samples were irradiated with UV light. The color of the irradiated samples was measured after each irradiation period, and it was found there was no color change of the shielded samples after the experimental period. IRRADIATION OF RED HAIR CROSS SECTIONS Three red hair fibers were fixed between two plastic plates and cut with an ultramicro­ tome to expose the hair cross sections in the way described in the previous paper (1). Twelve samples were prepared in this manner and divided into three groups. Four of the samples were shielded from light, an additional four samples had cross sections irradiated with VIS light, and the final four samples had cross sections irradiated with UV light. Irradiation of the cross sections was carried out for 20 irradiation units. Two samples from each group were gently shaken in deionized water (100 ml) for 30 seconds. The cross sections from both washed and unwashed samples were observed using SEM (magnification: x 7,000). Ten SEM images were taken for each unwashed sample, and the number of melanin granules, together with the number of cavities where melanin granules had run out, were then counted. The percentage of melanin granules that disappeared was defined as: Percentage of disappeared melanin granules = Number of cavities I (Number of cavities + Number of granules) x 100 In those cases where only a partial solid remained in a cavity, it was counted as one granule. In order to ensure the data were reliable, over 1000 cavities and granules for each experimental condition were counted. Percentages were calculated for each image and then averaged. COLOR MEASUREMENT The lightness (L) values of the samples were measured using a chromameter CR-300 (Minolta Co., Ltd., Osaka, Japan), according to the CIELAB system (illuminant C, 2° standard observer). The lightening degree (� L) was calculated as follows: �L = Lt - L0 where L0 is the L value of the untreated sample and Lt is the value of the treated sample.

PHOTOLIGHTENING MECHANISM OF RED HAIR 51 SEM EXAMINATION A JSM-6330F SEM CTEOL Ltd., Tokyo, Japan) was used and samples were coated with Au (200A) prior to observation. RES UL TS AND DISCUSSION PHOTOLIGHTENING OF RED HAIR The lightening behavior of irradiated red hair is shown in Figure 2. For comparison, the result from irradiated blond hair (1) is shown in Figure 3. It was quite interesting to find that UV light did lighten red hair but did not lighten blond hair without washing. Conversely, VIS light lightened both red and blond hair regardless of whether they were washed or not. In all cases the washing process accelerated the lightening. Comparing red and blond hair, it was found that the lightening level caused by UV light was higher for red hair than for blond hair, while the lightening caused by VIS light was higher for blond hair than for red hair. This result obviously indicates that the photosensitivity of melanin in red hair is dras­ tically different from that of melanin in blond hair, especially regarding UV sensitivity. PHOTOCHANGE OF RED HAIR CROSS SECTIONS A cross section of red hair is shown in Figure 4, which shows melanin granules and cavities where the granules originally existed. The photosensitivity of chemically intact melanin granules, which are exposed in the cross section, was measured using the previously devised method (1). �L �L b 6 6 5 ....... ·-0-lJV -+-VIS 4 4 o UV 3 3 2 2 1 1 0 0 -1 -1 irradiation units irradiation units Figure 2. Lightening degree of irradiated red hair. a: Irradiation was carried out without washing. b: Irradiation was carried out with washing.