CHEMICAL AND PHOTO-OXIDATIVE HAIR DAMAGE 385 lO 20 40 6• 80 Distance (•m) 6O so 40 20 1o b 0 20 40 60 80 Distance (Inn) so • 30 20 10 0 ., 0 20 40 60 80 100 120 Distance (Inn) Figure 2. Micrographs and fluorescence emission profiles of diffused uranine (5.5 h) in (a) untreated hair and in hair fibers exposed to (b) 200 h and' (c) 600 h of UV/humidification cycling.

386 JOURNAL OF COSMETIC SCIENCE • 45 • 40 • 35 = 30 • 25 r• 2o .• 15 • 10 • 0 :1 I I I Pre•reatments Figure 3. Effects of chemical and photochemical oxidative processes on diffusion kinetics of uranine in human hair. the hair fiber has occurred during the short-term treatment, and little or no significant additional damage is inflicted, because of the loss of hydrogen peroxide by side reactions. The newly obtained diffusion coefficient for the untreated hair fiber agrees well with the value obtained in the earlier work. The plot and table clearly show that the oxidative damage in hair fibers exposed to short-term (200 and 300 h) UV/humidification cycling is less than that of hair fibers bleached for one and four hours. However, hair fibers exposed to long-term (500 and 600 h) of UV/humidification cycling show greater oxidative damage than from both one and four hours of bleaching with peroxide. In general, long-term exposure to UV radiation results in damage greater than that ob- served for hair bleached with hydrogen peroxide, but less than that for hair bleached with hydrogen peroxide and ammonium persulfate. It has to be pointed out, however, that each of the diffusion coefficients listed in Table I and shown in Figure 3 is an average value along the diffusion front of uranine into the hair shaft of several hair fibers. It is therefore important to look at the diffusion coef- ficients of uranine into an individual fiber because of the significant variation in diffu- sion coefficients within a given fiber. In the UV-exposed fibers, diffusion coefficients show a clear skin/core differentiation. As can be seen in Figure 4, the diffusion coefficient in the fiber periphery is significantly higher than that in the core of the fiber. This may be due to two reasons: (a) This gradient may be due to greater oxidative damage in the fiber periphery than in the fiber interior, which in turn results in greater fiber swelling