420 JOURNAL OF COSMETIC SCIENCE 9()-.-------------------------------------, 80 -----------------------------1 Avobenzone -a 70+---------------=�-==----------------I CD .cl 0 60+--------------::-.,,,,::.-----------------------1 u, .cl !50-t-------------------------------------1 .c en ���--��-----------�--������-----I ::I Benz-4 :30+--��-----�----:::--o,::::_--------:�---=---------=-:-:-=----------1 ::, · · · · · · · · · -;;e 20+-------.,-----------:::aJll"'l-,::__--:::a.,..=----=--..-----,,------!!..•__.!•:........:.._•_•_._._.---=--:-:-----,=-:--::--:--I CmalTIQOpmpyl Trineth'JI 10 0 0 10 mg absorber/gm hair Amin.Cl 20 30 Figure 8. Calculated proponion of attenuated UVB and UV A light (290--400 nm) as a function of the amount of photo-absorber deposited on the surface of hair. amount of UV photo-absorbers deposited on the hair. The data show that UVB absorbers such as dimethylpabaimidopropyl laurdimonium tosylate, cinnamidopropyl ammonium chloride, and octyl methoxy cinnamate absorb less than 25% of the total UV radiation. This is because UVB (290-320 nm) constitutes only about 9% of the total solar radiation in the UV range. As might be expected, the compounds with a greater UV A absorbance (benzophenone-3, benzophenone-4, and butyl methoxydibenzoylmethane) absorb a greater percentage of the radiation between 290 mm and 400 nm. It has to be stressed that the theoretical assessment of the performance of various photofilters pre­ sented in Figure 8 assumes that they are characterized by perfect photostability. Such an assumption is justified in the case of materials such as benzophenone-3 and benzophe­ none-4. For butyl methoxydibenzoylmethane, which is very unstable under irradiation, the results of the calculation probably overestimate the capacity of this compound to absorb UV light under practical usage conditions. In a series of experiments, tresses of natural white hair dyed with a medium auburn dye were treated with leave-in aqueous or ethanol solutions of benzophenone-3 and benzo­ phenone-4, respectively. Figure 9 presents a gradual decrease in L1E as a function of the concentration of benzophenone-3 after 16 hours of irradiation and two shampooings. Figure 10 is a plot of percent color protection (calculated according to equation 3 from the experimental data) for both benzophenone-3 and benzophnone-4 as a function of the calculated extent of UV attenuation (calculated from spectroscopic data by using equa­ tion 4) by a given treatment. Extrapolation of the linear least-square fit to the data points suggests 72% color protection for 100% UV attenuation. This is in reasonable agree­ ment with the 63% protection observed in an experiment in which glass filters were employed to completely eliminate UV radiation (Figure 7), but it has to be kept in mind

FADING OF ARTIFICIAL HAIR COLOR 421 10 9 8 ) 15% 26.2% 21.3% Cl) 7 34% ca 6 ('\ (J ... 5 (J 4 3 2 1 0 I I I I 0 1 2 3 4 5 %Benz-3 Figure 9. Color changes in dyed hair treated with formulations containing benzophenone-3 at various concentrations. Percent protection is indicated for each data point shown in the figure. Data were obtained for white hair tinted with a medium auburn hair dye and treated with a 0.5 formulation per 1 g of hair. Irradiation time was 16 hours (two shampooings). that the experiment employing organic photofilters included two shampooings in ad­ dition to irradiation. It should also be pointed out that hair-color protection products containing high con­ centrations of photofilters (above 5% w/w) may lead to excessive modification of hair tactile properties. Such formulations cannot be designated as everyday treatments but only as special-use, color-protection leave-in lotions or fixatives for use during the time of highest-intensity solar exposure. HAIR COLOR PROTECTION BY A COMBINATION OF PHOTO FILTERS We have also investigated multicomponent photoprotection systems containing two photo-absorbers, such as benzophenone-3 or benzophenone-4 and zinc oxide. It was anticipated that a combination of an organic photofilter and an inorganic photofilter/ scattering agent might result in a synergistic effect similar to that reported for sunscreen formulations designed for skin protection (20-22). In one experiment, white yak hair was dyed with a light auburn dye, treated with a leave-on formulation containing a total of 3% UV absorber (benzophenone-3 and ZnO), and subjected to two eight-hour irra­ diation/shampooing cycles. The greatest color protection was observed for the mixture of 1.5% benzophenone-3-1.5% ZnO, and it was greater than the protection offered by an equal concentration of either ZnO or Benzophenone-3 alone (Figure 1 la). The use of