JOURNAL OF COSMETIC SCIENCE 386 at higher levels of hydration (15). Trp fl uorescence is known to be extremely sensitive to its immediate environment, and may increase or decrease depending on the mobility of the Trp residues. One may even observe an increase in Trp fl uorescence when hair is sub- jected to damaging treatments such as permanent waving due to the cleavage of disulfi de bonds. Although one may expect less Trp to be present after such a damaging treatment, such an effect may be explained by an increase in the mobility of Trp residues in the pro- tein in the absence of disulfi de bonds (17). In hair, we observe several distinguishable fl uorescence peaks when examining the spec- trofl uorescence excitation–emission matrices. Trp is the most familiar with an excitation wavelength of 290 nm and an emission maximum between 335 and 345 nm, depending on the degree of pigmentation—the greater the pigmentation, the longer the wavelength of the peak maximum. In previous studies, we identifi ed several emission peaks in the UVA–visible region that could be attributed to Trp metabolic/degradation products, in- cluding N-formylkynurenine, kynurenine, and 3-hydroxykynurenine (15). Figures 5 and 6 provide excitation–emission matrices for dark brown and Piedmont (white) hair. The difference in melanin content between these two samples greatly affects the spectrofl uo- rescence thumbprint. In dark brown hair, the Trp peak (Iex = 290 nm, Iem = 343 nm) appears as a minor constituent next to the large conglomerate of the kynurenines (Iex = 366 nm, Iem = 433 nm). Such a greater fl uorescence emission in the case of the kynuren- ines may be attributed to either higher concentration of these fl uorophores or less quench- ing by melanin (as compared to Trp where melanin absorption is greater). In the case of Piedmont hair (Figure 6), the Trp peak appears to be barely present (Iex = 292 nm, Iem = 337 nm) due to its miniscule emission relative to the kynurenines (Iex = 378 nm, Iem = 448 nm). More than likely, this is an optical effect in which case less melanin allows much greater fl uorescence for all fl uorophores in the tissue. Melanin has a monotonically de- creasing absorption spectrum when going from shorter to longer wavelengths. Contrary to intuition, it appears to infl uence the fl uorescence of the kynurenines to a greater extent than Trp. In the sections below, we compare peak intensities for Trp and the kynurenines from vir- gin hair with those of hair subjected to damaging treatments. We report the intensity of Trp, the kynurenines, and a degradation product of the kynurenines (I509). We also exam- ine the ratio of these peaks to better understand the effects of these treatments on protein degradation. Figure 5. Spectrofl uorescence excitation-emission matrix of dark brown hair.

HAIR SHAPE AND DAMAGE FROM RE-SHAPING HAIR 387 THERMAL DEGRADATION OF HAIR Frequently, hair is exposed to thermal treatments to provide a desired hair set or style. In previous studies, we found that hair experiences surface (cuticular) and internal (cortical) damage as a result of thermal treatment (7). Hair also undergoes color changes on expo- sure to heat. This is clearly evident in the photograph of Piedmont hair shown in Figure 7, where one can visually observe the region of the tress where the hot iron treatment was administered, resulting in the formation of a dark yellow hue. In the case of dark brown hair, we do not observe a visually signifi cant color change, probably because it is masked by the absorption of melanin. Thermal treatment was administered for 1 min of Figure 6. Spectrofl uorescence excitation-emission matrix of Piedmont hair. Figure 7. Photographs of thermally exposed Piedmont and dark brown hair.