HAIR DAMAGE PREVENTION BY COCONUT OIL 335 loss as compared to straight hair. This is mainly due to greater comb-hair interactions of a frictional nature in curly hair as compared to straight hair. WATER-RETENTION INDEX The water-retention index of undamaged hair is shown in Figure 7. From the data it can be seen that coconut oil reduces the WRI by 2-5%. Since coconut oil was used as a prewash conditioner, it would be reasonable to conclude that the effect may be due to oil residues left in the hair. The data for the bleached and boiling-water-damaged hair are shown in Figures 8 and 9, respectively. For these damaged samples, the WRI is much higher than that for the undamaged hair. This is mostly due to chemical degradation of proteins, generating hydrophilic groups. Both cleavage and oxidation of disulfide bonds, 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. Assuming that most of the water is absorbed by the fiber, the WRI reflects the swelling propensity of hair. Since repeated swelling and contraction damage the cuticle, reduction in the WRI can be considered as beneficial in reducing hair damage. The data in Figures 8 and 9 show that the sequence of application (whether pre- or postwash) is important. Postwash application is less effective in reducing the WRI as compared to prewash application. The difference seems to be in the location of the oil residues. In postwash application the oil film is on the surface, with no penetration into the fiber. In prewash application, because the fiber is swollen after the application of the 1'6 •o 2 o 14.10 12.10 ß 9.02 ß 8.42 De M½o S trmght Wavy Curly HAIR TYPES r--I With Coconut Oil •,•Without Coconut Oil J Figure 7. WRI of various hair types: Effect of coconut oil as a prewash conditioner.

336 JOURNAL OF COSMETIC SCIENCE X 60 z z LI.I 3o 20 (:• •0 .• o 55.03 •• 38.02 • 31.6 2 • 27.23 • 1'9,68 20,00 20.19 14.35 T • • -- 13.62 15,0 7 16.15 DaMco Straicjht Wavy Curly HAIR TYPES W(thout Coconut Oil [•'lWith Coconut Oil as Postwash ['-I With Coconut Oil as Prcwash Figure 8. WRI of bleached hair with coconut oil as a pre- and postwash conditioner. 80 74 ,•4 64.92 61.07 57,19 52,35 , 55•j 53.59 ß ß 49,15 39,12 x 70 60 50 40 30 20 10 0 De M½o 5trai cjht Way y C u rl y HAIR TYPES []Without Coconut Oil E•]With Coconut Oil as Postwash [--IWith Coconut Oil as Prcwash I Figure 9. WRI of boiling-water-damaged hair with coconut oil as a pre- and postwash conditioner. oil, it is possible that the molecules of the oil penetrate into the cuticle and probably even 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 triglyceride into the keratin structure.