210 JOURNAL OF COSMETIC SCIENCE PHOTO-OXIDATION OF HUMAN HAIR PHOTO DAMAGE: ITS CHARACTERIZATION/ QUANTIFICATION AND ALLEVIATION Sigrid B. Ruetsch, Ph.D. and Yash K. Kamath, Ph.D. TRI/Princeton, Princeton, NJ 08542 Introduction - When exposed to sunlight, the human hair undergoes changes in morphological, chemical, mechanical and cosmetic properties. The hair becomes dry, brittle, dull in appearance and rough to the touch. The work in this study involves simulated sunlight, optimized at 340 nm in the UVA region. The extent of UV radiation-induced damage to unprotected human hair is characterized as well as quantified using different methods. In addition, the performance of UV absorbers (sunscreens) is evaluated in terms of their diffusion behavior and their effectiveness in being able to provide protection to the keratin fiber against photodegradation. The results clearly show the importance of diffusion behavior, distribution and concentration (uptake levels) of the UV absorbers throughout the hair fiber cross sections with regard to their protective effect. Uniform distribution and high concentration levels are the prerequisite for successful performance. Techniques and Results - Scanning electron microscopy is used to highlight drastic changes in the physical nature of the hair fiber surface and interior as a result of long-term and short-term UV exposure. Longterm exposure to UV radiation/humidification cycling leads to collapsed and thinned out surface cuticle cells, fused firmly to the underlying cuticles, Figures 1 a-b. 33 'IK 4.3 30503S 5. 0 kV x4. 0•k'' •: Fig. 1 a-b Typical topography of unaltered hair before and after exposure to UV radiation/humidification cycling. Gradation of damage in the cortex as a function of progressive UV exposure is characterized and quantified using a microspectrophotometric technique. Changes in dye diffusion rates characterize/quantify UV radiation-induced morphological changes in the keratin fiber. The higher the dye diffusion rate, the greater the changes in fiber morphology, the greater the damage.

2002 ANNUAL SCIENTIFIC MEETING 211 The degradation of the main classes of hair proteins by UV radiation is characterized by gel electrophoresis. The results strongly indicate that along with the degradation of proteins, there may be a parallel reaction, which leads to crosslinking. This decreases the solubility and eliminates the extractability of the crosslinked protein network. Figure 2 shows easy extraction of matrix, intermediate filament and high-molecular weight proteins from untreated different ethnic hair (lanes 2, 4, 6 and 8), and the elimination of extractability of all proteins after UV exposure (lanes, 3, 5, 7 and 9). UV microspectrophotometry is used to characterize and quantify UV radiation-induced degradation of the hair proteins, especially of the aromatic and ring amino acids, which absorb at the lower wavelengths but shift to higher wavelengths after UV exposure. These higher wavelengths represent the photo-oxidized amino acids (Figure 3). UV microspectrophotometry is used to map the formation of photodegradation products within the fiber cross section, to trace the diffusion behavior of UV absorbers in the fiber, and to establish their effectiveness in providing photostability to the keratin system. Fig. 2 UV radiation-induced elimination Fig. 3 UV radiation-induced photo-oxidation of protein extractability. of the hair proteins (spectrum shifts to higher wavelengths). The extent of long-term UV radiation-induced damage to the cortex and the effectiveness of UV absorbers in reducing such damage are evaluated by measuring the changes in tensile mechanical properties. Changes in torsion, bending, shearing and fracture behavior may be used as alternate techniques to measure the damage. We show that already short-term UV exposure severely modifies the properties of the cuticula. Such UV radiation-induced changes in surface chemistry are characterized by measuring changes in surface wettability (surface energy), as well as in fiber friction and coarseness. Conclusions - UV damage inflicted upon the cuticula, such as dryness, dullness and increases in fiber friction (roughness), may be repaired/remediated by the use of conditioners, humectants and moisturizers. Damage to the cortex may be prevented or at least retarded by the use of UV absorbers (sunscreens). However, their diffusion behavior, distribution and concentration in the keratin fiber are all important.