EFFECT OF CURLING IRONS 225 ways for the formation of yellow-colored chromophores (17-19). In the case of thermal degradation, the process of yellowing is accelerated at high pH levels and can be controlled under acidic conditions or in the presence of certain reactive reagents, such as maleic anhydride or various antioxidants (20,21). Our results, discussed below, indicate that white, Piedmont, and bleached hair also experience yellowing as a result of short- term thermal treatments induced by hot irons. The objective of this communication is to analyze hair damage resulting from the use of conventional curling irons. We have employed fluorescence spectroscopy to quantify the decomposition of hair chromophores (i.e., Trp), and color analysis to measure the extent of color changes resulting from thermal treatments. In addition to this, combing mea- surements were used to detect changes in the fiber frictional properties of hair, which could reflect thermal damage to the surface elements (e.g., surface lipids) of the fiber structure. EXPERIMENTAL INSTRUMENTATION Thermal treatment of hair was performed using curling irons purchased from several manufacturers. We have elected to refer to these as curling iron A, curling iron B, curling iron C, and curling iron D. Figure 1 presents a dependence of temperature as a function of temperature setting for the four appliances employed in this work. The results indicate that the temperatures produced by these devices can range from 80øC to 300øC. These measurements and the analysis of similar appliances suggest that a more typical range is 130øC to 170øC. Within these limits, the process of hair drying occurs very rapidly, and fiber damage may be controlled by proper timing, even at 170øC. In order to maintain uniformity of the experimental conditions and to assure reproduc- ibility of the obtained data, the thermal treatment to each hair tress was administered in the same position, as indicated by the discolored band present on the hair tresses in Figure 9. Throughout this report we will refer to intermittent and continuous conditions with respect to the mode of curling iron application. Intermittent are those conditions in which heat treatment of a short duration (15 s) was applied to hair. Between each treatment interval the tresses were rinsed and towel-dried to a moist condition. The sum of all heating cycles constitutes a total treatment time. Continuous conditions of thermal exposure, on the other hand, represent the case in which a tress (initially containing 15-25 % water) is subjected to thermal exposure for a long period of time, typically 5-15 rain, without interruption. The intermittent mode of treatment emulates consumer usage conditions more closely than the continuous mode. Several experiments, discussed in subsequent paragraphs of this paper, were designed to compare the extent of hair damage resulting from both procedures. Fluorescence measurements were performed using a Fluorolog-2 fluorescence spectro- photometer (Model 212) manufactured by Spex Industries, Edison, NJ. The experimen- tal conditions were similar to those described previously (4). We used a bifurcated fiber optics probe to collect the spectra directly from the surface of hair. The emission and excitation slits were set at 2-nm bandpasses. The measurements were performed in both emission and excitation modes by irradiating hair in the wavelength range of 290-380

226 JOURNAL OF COSMETIC SCIENCE 350 300 250 E i•, 150 lOO 5o O Curling Iron A [] Curling Iron B O Curling Iron C X Curling Iron D x x o ¸ 0 oooooo oøø0 x E] o o o o o 0 2 4 6 8 10 12 14 Temperature Setting # Figure 1. Temperature profile comparison of several commercially available curling irons. 16 nm. This range of wavelengths was monitored in order to probe hair chromophores absorbing and emitting light in various parts of the UV/Vis spectrum. Spatially resolved combing analysis was achieved using a miniature tensile tester (Model 160), manufactured by Dia-Stron, Ltd., Hampshire, UK. The combing measurements were performed on wet hair with the following instrumental parameters: range, 2000 G gauge, 2 G sample size, 50 mm phase 1 (extension), 350% phase 2, 0% phase 3, 0%