188 JOURNAL OF COSMETIC SCIENCE these processes are likely to be affected. It is, therefore, interesting to speculate that the kinetics and equilibrium parameters of this exchange may provide information on the structural integrity of the fibers. Figure 3 shows the effect of moisture on the NIR spectrum of hair in the 1900-nm region. This figure clearly shows that the intensity of the band at 1935 nm can be used to measure both the dehydrating effects of heat, as in blow-drying or upon using a curling iron, as well as in water uptake by dried hair. It should be noted that heating the hair to 110øC for 90 min did not cause any apparent irreversible change in the water-binding properties of hair and that the process was totally reversible. Also, the bands due to protein that are used to normalize the data were also unaffected. This suggests that no apparent damage to protein, as judged by these markers, occurs under these conditions. A previous study on the use of NIR to measure water content of hair used second-derivative methods (12). We have chosen to use baseline subtraction of the raw spectra as the method of choice because it is simple, straightforward, and as the data show, not influenced significantly by the protein bands. The derivative method, we feel, is complicated when deconvolving bands of differing bandwidths. Hair treatments, particularly the "leave-in" kind, may affect the water-binding proper- ties of hair. Mechanistically, this may result from one or more of a variety of effects, such as the interaction of the product with the hydrophilic sites in hair, or be due to the hydrophobicity of the product, etc. The result of such an experiment is seen in Figure .40 .30 .20 .10 .00 (6) O) (5) (4) (2) i L • 1900 1950 2000 2050 2100 Wavelength (nm) Figure 3. Changes in the ambient hair spectrum (1) upon heating at 110øC for 90 min (2), followed by water regain in a room, maintained at 20øC and 50% RH, after 5 min (3), 10 min (4), and 75 min (5). The hair tress was then soaked in water and dabbed with a paper towel, and the spectrum was measured (6).

NEAR-INFRARED SPECTROSCOPY 189 4. It compares the results obtained with the untreated (control) half of a hair tress with the other half of the tress treated with a leave-in conditioning product. After the treatment the tress was heated at about 90øC for 30 min, following which the mea- surements were made (see Experimental section for details). As is clearly seen, there appears to be more water in the treated portion of the tress right after heating and for short water-take times, after which the two seem to converge. The data obtained after 24 h (infinite time) were indistinguishable from those obtained after 4 h, and have not been shown in the figure for clarity. The data obtained at 4 h at this humidity may, therefore, represent the equilibrium amount of water under these conditions. Thus, these data show that this product allowed more moisture to be retained in hair under the drying conditions of high temperature, similar to those encountered during blow-drying 100 - • 90 •- 70 o 60 o 0• 50 40 r'Y 30 0 50 100 150 200 Time (min) Figure 4. The water regain by hair as a function ooe time. The hair samples were heated to 93øC for 30 min, following which they were measured in a room maintained at 20øC and 50% RH (see text for details). The 1935-nm band was normalized against a water-insensitive protein band. The open circles represent the treated site, while the open squares represent the untreated control. Notice that at early times the treated sample contains more water than the untreated control, but that the two converge as the system approaches equilibrium.