536 JOURNAL OF COSMETIC SCIENCE 6OO 500 400 300. 200, lOO ! dV i i i Control UVA UV' Bleaching (Mercury) (Mercury) (Xenon) Figure 2. Breaking strength data for photo-oxidized (mercury-vapor and xenon lamps) and bleached hair samples. Box plots were obtained from 20 hair fiber measurements from each hair sample. strength reduction was observed, indicating that changes in the tx-keratin crystals of hair are mainly related to that range of the solar spectrum. Figure 3 shows the modulus data for mercury-vapor lamp photo-oxidized hair samples. An increase in modulus can be observed after exposure to the mercury-vapor lamp radiation, indicating a lower resistance of the fiber to deformation. Unexpectedly, no changes on this parameter were observed either in the samples exposed to xenon lamp radiation or in the bleached samples. CONCLUSIONS Damage caused by chemical and photochemical oxidation influences the same mechani- cal properties, with breaking elongation and breaking strength as the main parameters affected by both treatments. 10 1 , & , Control UVA (Mercury) (Mercury) Figure 3. Modulus data for mercury-vapor lamp photo-oxidized hair samples. Box plots were obtained from 20 hair fiber measurements from each hair sample.

EFFECT ON HAIR OF SUN AND BLEACHING 537 Changes in the stress-strain curves appear after only two bleaching cycles in the bleached samples, indicating that chemical oxidation causes faster cortex degradation than pho- tochemical oxidation. In this case, we also observe that changes in the hair mechanical properties are mainly related to the UVB range of the solar spectrum. ACKNOWLEDGMENTS The authors thank FAPESP (Grant 01/14161-9), CAPES, and EVIC for financial sup- port. REFERENCES (1) C. R. Robbins and R.J. Crawford, Cuticle damage and the tensile properties of human hair,J. Co, met. Sci., 42, 59-67 (1991). (2) P. Zuidema, L. E. Govaert, F. P. T. Baaijens, P. A.J. Ackermans, and S. Asvadi, The influence of humidity on the viscoelastic behaviour of human hair, Biorheol., 40, 431-439 (2003). (3) Z. D. Draelos, The biology of hair care, Dermatol. Clinics, 18, 651-658 (2000). (4) S. B. Ruetsch, Y. Kamath, and H. Weigmann, "Photodegradation of Human Hair: A Microscopy Study," in Sun Protection in Man, P. U. Giacomoni, Ed. (Elsevier, Amsterdam, 2001), pp. 175-205. (5) C. R. Robbins, Chemical and Physical Behavior of Human Hair (Springer-Verlag, New York, 2002), pp. 160-180. (6) C. M. Pande and J. Jachowicz, Hair photodamage: Measurement and prevention,J. Soc. Cosmet. Chem., 44, 109-122 (1993). (7) S. Ratnapandian, S. B. Warner, and Y. K. Kamath, Photodegradation of human hair,J. Cosmet. Sci., 49, 309-320 (1998). (8) A. C. Santos Nogueira and I. Joekes, Hair color changes and protein damage caused by ultraviolet radiation,J. Photochem. Photobiol. B. Biol., 74/2-3, 109-117 (2004).