HAIR PHOTOPROTECTION BY DYES 387 .4- z i Unexposed • 96 h exposed S--S Stretching mode 600 550 500 450 400 Wavenumbers (cm Figure 7. Changes in the intensity of the band associated with the disulfide (S--S) stretching mode of hair keratin upon photo-exposure of Piedmont hair. The amount of damage is calculated from changes in the height of this band at ca. 510 cm -•. predict apriori. Since most commercial products use similar dyes and precursors, and the chemistry involved in oxidation dyeing is similar, the results are likely to be qualita- tively similar. Some subtle and quantitative differences may, however, exist, depending on the precise combination and the use of certain unique and product-specific dyes. The pattern of dye deposition within a fiber is another factor that can affect the efficacy of photoprotection. Although this depends on the dye structure to some extent, the pH and other ingredients in the formulation can also play an important role. For example, we have found that the black shades of oxidation dyes at pH 9.5 penetrate the hair fibers quite well, while at pH 7 most of the color is localized close to the surface. These differences in the dye distribution affect the appearance of color and the fading charac- teristics and, as a result, they will likely affect the efficacy of photoprotection.

388 JOURNAL OF COSMETIC SCIENCE 12 Untreated SP 1 (mue) SP 1 (Red) SP2(Red) Figure 8. Comparison of the effects of photo-exposure on undyed and dyed Piedmont hair. In this case the hair was dyed with semipermanent products SP1 and SP2. CONCLUSION We have shown that commercial hair-dyeing products, used either for gray coverage or to enhance the natural hair color, provide an additional and less-appreciated benefit of protection against sun damage. This effect is seen for both unpigmented and pigmented hair, and with semipermanent as well as oxidation dyes. In general, within a product type, the darker the shade the higher the degree of protection. We believe that hair dyes, particularly the direct or the semipermanent type, could be used effectively to protect hair against sun damage. In fact, dyes have been used in the wool industry to protect against phototendering (14). The methodologies discussed here can help formulators optimize the efficacy of the products and help marketers in making novel claims. REFERENCES (1) C. Robbins, Chemical and Physical Behavior of Human Hair (Springer-Verlag, New York, Berlin, Heidelberg, 1988). (2) C. Zviek and R. P. R. Dowber, "Hair Structure, Function and Physical Properties," in The Science of Hair Care, C. Zviek, Ed. (Marcel Dekker, New York, 1986), pp. 1-48. (3) J. Jachowicz, Hair damage and attempts at its repair, J. Soc. Cosmet. Chem., 38, 263-286 (1987). (4) C. Pande and J. Jachowicz, Hair photodamage: Measurement and prevention,J. Soc. Cosmet. Chem., 44, 109-122 (1993). (5) E. Hoting and M. Zimmerman, Sunlight-induced modifications in bleached, perreed, or dyed human hair,•/. Soc. Cosmet. Chem., 48, 79-91 (1997). (6) E. Hoting, M. Zimmerman, and S. Hilterhaus-Bong, Photochemical alterations in human hair. I. Artificial irradiation and investigation of hair proteins, d. Soc. Cosmet. Chem., 46, 85-99 (1995).