316 JOURNAL OF COSMETIC SCIENCE 5O e 30 • 2O 10 0 i • i 100 hours 200 hours 300 hours 0 20 40 60 80 % RH Figure 4. Reduction in work-to-20%-strain of Piedmont hair exposed to simulated solar radiation. 50 ß 40 • 30 ß • 2O 10 ß 100 hours ß 200 hours ß 300 hours 0 20 40 60 80 % RH Figure 5. Reduction in stress-at-20%-strain of Piedmont hair exposed to simulated solar radiation. ANALYSIS OF THE FTIR SPECTRUM The FTIR/ATR spectra obtained from Piedmont hair exposed for 300 hours at different RH levels are shown in Figure 7. The spectra were normalized using the absorbance at 1513 cm -1 (peak 1), the amide-II band, allowing a semiquantitative comparison of the cystine oxide content. A listing of the different absorbance peaks is given in Table III (2). The absorbances at 1042 cm 1 (peak 5) due to cysteic acid and at 1073 cm -• (peak 4) due to cystine monoxide, the primary degradation products of the disulfide links, indicate that irradiation at 20% RH caused the least amount of degradation. These absorbances for fibers exposed to radiation at other RH levels are essentially invariant, as shown in Figure 7. Since the beam essentially penetrated only the cuticle, the results suggest that damage to the cuticle is nearly identical for irradiation under different conditions over similar duration of exposure. This concurs with the results reported by Hoting eta/. (2). The low absorbances shown for exposure at 20% RH are probably due to experimental error. An important point to be noted is that cuticular damage, unless excessive, does not affect the tensile properties significantly (16). However, such damage is often the cause of crack initiation and fiber fracture. ROLE OF MOISTURE IN HAIR PHOTOLYSIS According to Arnaud (17), photolysis of hair proteins is caused by radiation with

PHOTODEGRADATION OF HUMAN HAIR 317 8O 03 70 '-- 6O '- 40 • 30 ß • 20 y = -0.0616x 2 + 5.2888x - 35.693 R 2 - 0.9982 0 10 20 30 40 50 60 70 RH (%) Figure 6. Diametral swelling of Piedmont hair exposed for 300 hours at different relative humidities. Bio-Rad Win-IR .1- 1 I I 310 I I I 1500 1400 1 0 1200 1100 1000 Wavenumber (cm-1) 20, 30, 50 and 70 indicate %RH during exposure Figure 7. FTIR/ATR spectra for Piedmont hair exposed for 300 hours at different relative humidities. wavelengths in the range of 254 to 350 nm. The absorption spectrum for Piedmont hair, shown in Figure 8, indicates this range to be the primary absorption region of unpig- mented hair. Radiation of this wavelength can also initiate free radicals by Fenton's reaction involving iron, oxygen, and water. This is consistent with the suggestion that photolysis of hair keratin can follow the free-radical pathway as proposed by Tolgyesi (1) and Wei (7). A steady-state analysis suggests that the rate of photolysis of hair should vary with the square root of the concentration of the "initiator." Assuming that hair contains small but uniform amounts of free-radical initiator (im- purities) and that hair photolysis follows the proposed hypothesis, the damage will