ISOLATION OF CUTICLE 285 Figure 2. Scanning electron micrograph showing the surface of DS-2'. Refer to Table I for experimental conditions. outermost layer disappears. Even on the inner side of the cuticle layers, the boundary becomes more obscure than in DS-1. Based on the above observations, the mechanism of the isolation of the cuticle can be inferred as follows: 1) the boundary between the exo- and endocuticles in a few outer layers becomes obscure at first, and the thickness of one layer decreases to less than half of the virgin cuticle 2) the change occurs with the simultaneous dissolution of the outermost layer 3) the boundary between the exo- and endocuticles becomes obscure even on the inner side of the layers, with the thickness kept unchanged, suggesting partial dissolution in the layer and 4) the dissolution proceeds from the outer layer to inner layer, successively accompanied by the complete disappearance of the boundary between exo- and endocuticles in the inner layer. No cuticle cells are observed both in DS-3 and DS-4, as shown in Figures 3d and 3e, respectively. The boundary between the cuticle and cortex is no longer detected, and the cortical cells are partially dissolved, particularly in DS-4. The rough surface detected in DS-3 by an SEM micrograph (Figure ld) arises from the partially dissolved cortical cells. The only difference in the treatment condition between DS-2 and DS-2' is the concen- tration of KOH. It is noted that the cuticle layer in DS-2' shrinks and the cuticle thickness is apparently decreased despite the equal number of layers (Figure 3f). This means that the dissolution occurs simultaneously on the inner side of the cuticle layer. The higher concentration of KOH may not be preferred for mild removal of hair cuticle, because dissolution may reach the cortex without isolation of cuticle layers. It is noted that the smooth surface observed from the SEM micrograph does not always mean the complete removal of cuticle when we compare SEM with TEM micrographs for DS-2 hair in Figures lc and 3c, respectively. RELATION BETWEEN CUTICLE THICKNESS AND REACTION TIME Although the total treatment time of DS-2 is the same as that of DS-l, the extent of

286 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS (a) 1,OlJm (b) (c) 1.01•m (d) 1,Op• (e) (f) Figure 3. Transmission electron micrographs showing cross section of cuticle cells: (a) untreated hair and (b) DS-I, (c) DS-2, (d) DS-3, (e) DS-4, and (f) DS-2' hair. elimination of cuticle cells is greater in DS-2 than in DS-1. This is due to the longer treatment at 50øC for DS-2. In Figure 4, the relation between the total thickness of cuticle cells and the total treatment time at 50øC is shown. For DS-1 and DS-2, cuticle thickness is directly measured by TEM microphotographs. For DS-3 and DS-4, the