418 JOURNAL OF COSMETIC SCIENCE The observed difference in shampoo fading of hair treated with product (IV), containing 1-hydroxyethyl-4,5-diamino pyrazole sulfate, and hair treated with products (I) or (II) can be probably explained by the higher water solubility of the dye products formed in hair as a result of the use of (IV). One should also point out that the mechanism of reactions involving pyrazolone coupler and its role in the formation of red color was not fully elucidated (12). It was suggested that the material does not participate in the final color formation. An additional complication in the interpretation of the data is the use of ethanolamine and ammonia as alkalizing agents in formula (V), which may affect the dye penetration into the hair. COLOR FADING BY UVB AND UV A It is a common practice to include UV absorbers in hair-care formulations designed for treatment of dyed hair. While visible light can also cause fading, visible-light absorbers are colored, which precludes their use in commercial products. The relative color-fading efficacy of various segments of solar radiation (UVA [320-400 nm}, UVB [280-350 nm}, visible [370-780 nm}, and IR [750-2800 nm}) was investigated by Hoting and Zimmerman for red-colored hair (6). They found that the photo-fading efficiency per 1 W/m2 of light intensity (calculated as dB/(light intensity [W/m2})) is the greatest for UVB (0.38 m2/W) and the smallest for IR (0.0019 m2/W), with a relative efficiency varying in the following order: UVB UVA Vis IR. However, considering the relative intensity of various portions of radiation, which were chosen to approximate the intensities of natural summer sunlight in central Europe, the actual photo-fading effect expressed as dB equaled 8.5, 3.8, 0.95, and 0.84 for hair subjected to visible, UVA, UVB, and IR light irradiation, respectively. Thus the contribution of UVB and UVA to the total photo-fading effect is about 34%. In order to determine if filtering off UV radiation from natural light would result in noticeable color protection, we irradiated hair with simulated solar light passing through special filters such as a Schott glass-type GG 420 UV filter, which effectively blocks UV light (-0% transmission below 390 nm), and the quartz filter, which is nearly transparent to light with a wavelength above 290 nm. White hair treated with a commercial medium auburn dye (II) was employed in these experiments. Figure 7 shows the total color change of hair, dB1 after 16, 32, and 48 hours of irradiation. Hair samples covered with the UV filter showed -30-60% less color loss and were noticeably darker and redder than the samples covered with the quartz plates. The amount of protection offered by the UV filter is calculated from the formula 100 x (dBc - dBp) %Protection = d Ee (3) where dB c and dB p are the total color changes after the irradiation of unprotected (quartz filter) and UV filter-protected hair, respectively. Results presented in Figure 7 refer to hair samples that were irradiated without shampooing. It should be noted that the amount of protection varied in the range of 27% to 63%, depending upon the time of exposure. Longer irradiation times led to smaller photoprotection values. This result could be expected as a consequence of the existence of a limiting value of residual concentration of chromophores in a hair color, which are gradually depleted during photo-exposure (at sufficiently long exposures the coloration should completely fade

a) 12 7 0 10 FADING OF ART FICI .... HAIR COLOR 419 20 JO 40 50 lrr,adlation 1ime (Hr:&) 60 b) frer 8 hrs irradiafon Irradia1ed through quartz Irradiated through filter blocking UV light "igun: 7. Total color loss for white hair, dyed with medium auburn dye (a) and irradiated through a quartz filter and a filter completely absorbing UV light (b). away, and% protection would be reduced m zero). In summary, the present data confirm the previous suggestion that blocking UV light can ·ignificantly limit artifici, I hair­ color fading. THEORETI 'AL AND EXPERIMENTAL ANAI.YSIS OF PHOH R TECTION B UVA AND fJVB PHOT HlTER, The tht:oretical extent of phoroprotection by a formulation, containing phow-absorbers 'nd evenly disnjbuted on h, ir, can b� assessed by calcula1ting the percentage of UV lighr it absorbs. It can be shown that the attemntinn of li :i-ht, at a given wavelength, b, a multi-component photofilter , ystem is given by 1:he foJlowing: relationship, which is a modification of Beer's equation: wh. re / /"Ii.) is the ab, orbanc of _pho ofil t r i at wavelength A, l s(A) i the intensity of solar radiation, ep1.) is the molar extinction coefficient of )homfilter i at wavelen , h (A.), m i is the amoun of formulation deposited on hair (gig hair), C is i:he concentm -ion of a photofilter in a formulation (% w/w), J\ is the specific surface area of hair assumed to be 800 (cm2/g), p is the densiry of a dry formulation (assumed to be approximately 1 g/cm3 ), and /W u •i is th molecular weight of an i-�h photofil r. Equation 4 can be used to calculate the fraction of light absorbed at each wavel.ength by a given quantity of absorber on the hair. The total percentage of absorbed UV radiation can be determined by integrating (numerically) equation 4 over th wavelength range 29-0-400 nm. For calculations, values for the solar irradiation on the surface of the earth between ?90 mm and 400 nm were taken from the literature (19). figure 8 shows rhe _percentage of attenuated UVB and UV A light (290�/400 nm) as a function of the