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.

52 5 4 3 2 1 0 -1 JOURNAL OF COSMETIC SCIENCE -.-YI'-------- -u-uv irradiation units .6L b 5 -+-VIS 4 .,.o, .. UV-----+----+---,,-� 3 2 1 -1 10 20 30 irradiation units Figure 3. Lightening degree of irradiated blond hair. a: Irradiation was carried out without washing. b: Irradiation was carried out with washing. 1nelaningranules /1 cavities Figure 4. Cross section of red hair. Decomposition of melanin granules. The percentages of disappeared melanin granules from the non-irradiated, UV-light-irradiated, and VIS-light-irradiated samples are shown in Figure Sa. For comparison, the result from blond hair is shown in Figure 56 (1). After UV-light irradiation, the percentage of disappeared melanin granules increased by