FOURIER TRANSFORM INFRARED SPECTROSCOPY OF HAIR 71 The results shown in Tables VI and VII were obtained from a single analysis (--10 fibers) on each tress. Single values represent one analysis. Where apparent inconsisten- cies appeared, a range is given. Although these results were usually close, an example of an inconsistency is where a waved and weathered tress showed less oxidation than a waved and unweathered one. In spite of the relatively high uncertainty of a single determination, the general order of oxidation occurred as might be expected. Weath- ering alone caused relatively minor (although measurable) oxidation, while bleaching and weathering was 2 to 4 times more damaging than waving and weathering. Blond and brown hair were used in these studies, but no consistent trend was found as to which was more readily oxidized. It appeared that 12 weeks of outdoor weathering was comparable to about 2 weeks in the Weather-Ometer. EFFECT OF BLEACHES OF DIFFERENT STRENGTHS The effect of subjecting tresses to different bleaching intensities is shown in Figure 5. The cysteic acid content of these treated tresses was determined by measuring the absorbance ratio of 1042 cm-•/1650 cm -• and using Bit-Alkhas' calibration curve (Figure 1). These experiments suggest that a nearly linear relationship exists between the bleach intensity and the percentage of sulfur atoms oxidized to sulfonic acid. DISCUSSION If one assumes that the absorptivity of the sulfonate linkages in cysteic acid is the same as the S = O linkages in the thiosulfonate (Bunte salt), one can compare the results in Tables I and III. It appears that more disulfide linkages are attacked by the bisulfite waving process than by a single bleaching. For each broken disulfide linkage by oxi- dation we obtain two -SO• groups compared to one -S-SO• residue when a disulfide link is severed by bisulfite attack. The mean values in the last three columns of Table I should have twice the value of the same columns in Table III to account for Table VI Oxidation Levels of Hair in the Atlas Weather-Ometer Exposure 1042 cm- 1 Time Treatment Color 1076 cm- 1 2 weeks Heat, moisture, UV 4 weeks Heat, moisture, UV 0 Waved 2 weeks Waved, heat, moisture 2 weeks Waved, heat, moisture, UV 4 weeks Waved, exposed and unexposed 0 Bleached 2 weeks Bleached, heat, moisture 2 weeks Bleached, heat, moisture, UV 4 weeks Bleached, heat, moisture 4 weeks Bleached, heat, moisture, UV Blond Blond Blond Brown & Blond Blond Sh* Sh, O. 06 O. 08 0.22 0.46 0.25-0.62 1.17 1.35 1.70 1.9l-2.27 2.51 * Unresolved shoulder clearly larger than virgin hair.

72 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS Table VII Oxidation Levels of Hair After 12 Weeks of Outdoor Weathering* 1042 cm- • Treatment 1076 cm- • Unexposed (heat and moisture only) or Exposed (heat + moisture + UV) Waved unexposed or waved exposed Bleached unexposed or bleached exposed Sh-O. 12 o. 17-0.57 1.26-1.88 * Each group includes blond and brown hair. the splitting of the same number of disulfide groups. This was not the case, indicating that more disulfide bonds were attacked by bisulfite than by the bleaching process. Hair diameter is a parameter that affects the results. In a diamond cell, the entire hair fiber is viewed in transmission. Oxidative attack is likely to be concentrated in the cuticle and outer cortical cells. This is because of the impervious nature of the cuticle scales and because cystine is more concentrated in the cuticle than in the cortex, with very little found in the medulla (8, 16). Infrared analysis of hair in transmission will determine the oxidation of sulfur in the entire hair. A surface analysis method (such as multiple internal reflectance) would probably show higher percentages of oxidation and may even yield more reproducible results. 30- 2o u g_ o Bleach Strength Figure 5. Plot of percentage of sulfur atoms oxidized as a function of bleaching strength.