2006 TRI/PRINCETON CONFERENCE 387 performed using a spectrophotometer (GretagMacbeth Color-eye® 2180UV, New York, USA). The instrument configuration used was the same as previously described (12). Spectra provided values of coordinates L* (color lightness), a* (redness, if positive or greenness, if negative), b* (yellowness, if positive or blueness, if negative) from the CIELAB system of equations. From these, the color difference parameters, DL * (light- ness difference: lighter if positive, darker if negative), Da* (red-green difference: redder if positive, greener if negative), Db* (yellow-blue difference: yellowish if positive, bluer if negative) and DE* (total color difference: [(DL *2 + (Da *)2 + (Db*)2J 11 2 ) were calculated. Measurements were done keeping the same sample region and turning the hair sample in the instrument sample holder. Ten diffuse reflectance measurements were done for each sample. The internal reference was the average of a set of 10 measurements from control samples. Prior to reflectance measurements, the samples were conditioned at 50 ± 5% RH and 25 ± 2 °C for 24 h. MECHANICAL PROPERTIES Stress/strain curves were obtained from 40 fibers (5 .0 cm length, 24 h conditioning at 25 ± 2°C and 50 ± 5% RH) of each sample using a universal test machine (EMIC DL 2000, Sao Jose dos Pinhais, Brazil) with a 10 N load cell operating at 10 mm/min constant speed. The diameter of each fiber was measured after conditioning using a micrometer (Mitutoyo Ltd., Sao Paulo, Brazil). RES UL TS AND DISCUSSION COLOR CHANGES Figure 1 shows the average values of the lightness difference parameter (DL *) for the hair samples obtained after 16 and 64 days of 'sun exposure' (4 h exposure per day). As 20 White hair 15 ·c: 10 a, 5 :J -1 16 days 64 days Blond hair 16 days 64 days Dark-brown hair 16 days 64 days Figure 1. Average values of the lightness difference parameter (DL *) for white, blond and dark-brown hair obtained after 16 and 64 days of simulated sun exposure, considering 4 h exposure per day. Ten color measurements on each sample. UV exposed. D UVA exposed. ■ Unexposed.

388 JOURNAL OF COSMETIC SCIENCE expected, every hair became lighter after exposure. This change was more pronounced when UVB was cut out of the radiation system. Blond hair showed the greatest change, followed by white and dark-brown hair, respectively. Figure 2 shows the average results obtained for the yellow-blue difference parameter (Db*). Blond hair turns yellower after UV exposure, but not after UVB filtered radiation exposure. Dark-brown hair turns yellow after both UV and UVB filtered radiation exposure. Surprisingly, white hair turns less yellow after both UV and UVB filtered radiation exposure. Figure 3 shows the average results obtained for the red-green difference parameter (Da*). Dark-brown hair became redder after both exposure conditions. Blond and white hair showed an opposite trend, turning less red. Figure 4 shows the total color variation (DE*) obtained to the different hair type. Blond hair showed the greatest change, with DE* values on the order of 6.0 and 20.0 after 16 and 64 days of exposure, respectively. Total color difference values of about 3.0 for dark-brown and 10.0 for white hair were measured after exposure. Results show that hair color changes are mainly affected by UVA radiation in every hair type. According to Borges et al. (13 ), the total amount of melanin (eumelanin + pheomelanin) in blond and red hairs is about 2.5 mg/g hair, in dark-brown hair 5.2 mg/g hair and in black hair 7.2 mg/g hair. As expected, we observe that the hair color change increased with the decrease in melanin content. On the other hand, the observation of color changes on white hair (without melanin) after irradiation shows that the melanin type and content of each hair is not the only parameter related to hair damage caused by sun exposure. Keratin is also photosensitive. Among the keratin amino acids, tryptophan, cystine, tyrosine and histidine are more susceptible to photo-degradation. The total amount of these amino acids depends on hair type. Male hairs have more cystine than female and, usually, dark hairs have more cystine than light hairs (8). According to Bertazzo et al. (14), the amount of tryptophan in dark-brown and black hair is greater than in blond hair. The highest trypthophan concentration is found in gray and white hair, indicating that tryptophan concentration in hair increases with age. Vincenci et al. White hair Blond hair Dark-brown hair -1 ·c: -3 -5 -7 -9 16 16 64 64 16 64 days days days days days days Figure 2. Average values of the yellow-blue difference parameter (Db*) for white, blond and dark-brown hair obtained after 16 and 64 days of simulated sun exposure, considering 4 h exposure per day. Ten color measurements on each sample. UV exposed._) UVA exposed. Unexposed.