2006 TRI/PRINCETON CONFERENCE 2--,----------�--------��--------� White hair Blond hair -4 -5 �--------�--------��--------� 16 64 16 days 64 days 16 days 64 days days days 389 Figure 3. Average values of the red-green difference parameter (Da*) obtained for white, blond and dark-brown hair 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. White hair Blond hair Dark-brown hair ;­ 20 5 15 +I CII � 10 0 � 5 16 days 64 days 16 days 64 days days 64 days Figure 4. Average values of the total color difference parameter (DE*) 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. (15) studied red hair, observing that the amounts of pheomelanin and eumelanin vary with sex, age and color shade. In this way, it must be assumed that color changes are related not only to melanin photodegradation but also to protein photodegradation, in a way that is difficult to account by now. MECHANICAL PROPERTIES Figures 5 and 6 show, respectively, the breaking strength and breaking elongation data

390 JOURNAL OF COSMETIC SCIENCE White hair Blond hair Dark-brown hair )( 800 c? 6 600 )( C: � u5 400 � )( "iii C Q) I- 200 Figure 5. Breaking tensile strength data for hair samples after 64 days of simulated sun exposure, con- sidering 4 h exposure per day. The values are the average of 40 hair fibers measurements from each hair sample.� UV exposed.� UVA exposed. D Unexposed. 100 I White hair i Blond hair Dark-brown hair )( i i 90 $ i $I� )( )( +19 � 80 � C 0 � 0) 70 C: 0 iJj I i i i 0) i i C 60 i i � i )( i (1J i i Q) i i )( .... al i i 50 i i i i i i i i i 40 i i )( Figure 6. Breaking elongation data for hair samples after 64 days of simulated sun exposure, considering 4 h exposure per day. The values are the average of 40 hair fibers measurements from each hair sample. � UV exposed.� UVA exposed. D Unexposed. for hair exposed to different wavelength ranges. Both parameters were affected in all hair types, mainly by UVB radiation. A reduction of circa 7% and 15% was observed on breaking elongation in all hair types after UVA and UV exposure, respectively. Con- cerning breaking strength, a more pronounced reduction was observed on white hair, followed by blond and dark-brown hair, respectively. The same trend was found when UVB radiation was filtered. In this case, a smaller reduction on breaking strength was observed, indicating that changes in the a-keratin crystals of hair are mainly related to that range of the solar spectrum.