188 JOURNAL OF COSMETIC SCIENCE 24.2 % WATER RETENTION INDEX 10- COCONUT SUNFLOWER COCONUT SUNFLOWER OIL OIL OIL OIL PRE-WASH TYPES OF OILS POST-WASH •WITHOUT EIWITH Figure 8. Comparison of water retention index for hair treated with boiling water. WATER RETENTION INDEX The water retention index for undamaged hair is shown in Figure 6. From the data it can be seen that coconut oil reduces the WRI of undamaged hair by 44%, whereas in the case of mineral oil and sunflower oil, there is hardly any reduction in WRI, as seen in Figure 6. The ability of coconut oil to penetrate hair (4) supports this observation. The data for the bleached, heat-damaged, and UV-damaged hair are shown in Figures 7-9, respectively. For these damaged samples, the WRI is much higher than that for the undamaged hair. This is mostly due to the chemical degradation of proteins, generating hydrophilic groups. Both the cleavage and oxidation of disulfide bonds, followed by their oxidation to cysteic acid, as well as hydrolysis of the peptide linkage, occur, although the contribution of the latter is probably minor. All samples show a reduction in the WRI as a result of the application of coconut oil, whereas the same findings were not observed to a significant level in the case of mineral oil and sunflower oil. Assuming that most of the water is absorbed by the fiber, the WRI reflects the swelling propensity

EFFECT OF COCONUT OIL ON HAIR DAMAGE 189 % WATER RETENTION 40 INDEX i59.8 ß 5 60 x::":• 20- COCONUT OIL 61.2 61.2 SUNFLOWER OIL •,..•8.7 57.5 COCONUT SUNFLOWER OIL OIL PRE-WASH TYPES OF OILS POST-WASH EIWITHOUT EIWITH Figure 9. Comparison of water retention index for UV-treated hair. of hair. Since repeated swelling and contraction damages the cuticle, reduction in the WRI can be considered as beneficial in reducing hair damage. The data in Figures 6-9 show that the sequence of application (whether pre- or post- wash) is important. Post-wash application is less effective in reducing the WRI as compared to pre-wash application. The difference seems to be in the location of the oil residues and their ability to counteract surfactant damage. In post-wash application the oil film is on the surface, with no penetration into the fiber. In pre-wash application, it is possible that the molecules of the oil penetrate into the cuticle and probably even into the cortex. This may also be the case with undamaged hair, although the effect is small. The reduction in the WRI must be due to the introduction of the hydrophobic triglyc~ eride into the keratin structure. See Table VI for pair-wise comparison of treatment effects for water retention index data. MECHANISM OF PROTECTION BY COCONUT OIL AND NOT BY MINERAL OIL AND SUNFLOWER OIL The histology of a cuticle cell and the mechanism of damage in wet combing is proposed by Swift (5,6) Because of cross-linking, the exocuticle is brittle and does not swell. The