PENETRABILITY OF OILS IN HAIR 183 Figure 11. Increases in fiber diameter in untreated and oil-treated hair fibers during one-hour immersion in water, demonstrating the protective action of oils. decrease in swelling behavior as a result of the oil treatment. Figure 12 shows the inter-fiber averages. While both oil-treated categories show a significant decrease in swelling, it is slightly greater for the coconut-oil-treated fibers than the mineral-oil- treated specimens. In coconut- and mineral-oil-treated specimens, swelling is reduced by 48% and 33%, respectively. This strongly suggests that the fiber is protected from damage by hygral fatigue (swelling and de-swelling). It should be emphasized that the reduction in moisturization of the fiber does not make the fiber rigid because of the plasticizating action of the absorbed coconut oil. CONCLUSIONS This work has shown that the TOF-SIMS technique can be used to study the penetration 16/1 14 12 10 8 6 4 2 0 --= Untreated Mineral Oil Coconut Oil Figure 12. Averaged increases in fiber diameter in untreated and oil-treated hair fibers during one-hour immersion in water, demonstrating the protective action of oils.

184 JOURNAL OF COSMETIC SCIENCE of small diffusible molecules into the cortex of hair. Due to its polarity and affinity for the protein, coconut oil was found to penetrate into the hair cortex. Mineral oil, on the other hand, did not penetrate the fiber. The reason is likely to be its lack of affinity for the protein. Penetration of oils seems to reduce the hydrophilicity of the protein, as indicated by the lower amount of swelling observed in hair fibers treated with coconut oil. Mineral oil also shows lower levels of swelling compared to the untreated fiber, suggesting that it may have penetrated into the cuticular regions, thereby preventing further penetration of water into the hair shaft during the swelling experiment. Significant reduction in swelling suggests that this will prevent swelling and de- swelling (hygral fatigue) of the fiber. Hygral fatigue can lead to cuticular damage as well as damage to the cortex, which can, in turn, affect the mechanical properties. These re- suits support the beneficial effects of coconut oil to the hair observed in earlier work (1). REFERENCES 1. A. S. Rele and R. B. Mohile, J. Cosmet. Sci. 50, 327-339 (1999). 2. E. D. Goddard and J. V. Gruber, Eds., Principals of Polymer Science and Technology in Cosmetics and Personal Care (Marcel Dekker, New York, 1999), p. 469. 3. C. R. Robbins and K. M. Fernee, J. Soc Cosmet. Chem., 34, 21 (1983). 4. P. Stam, R. F. Katy, and J. R. White, Text. Res. J., 22, 48 (1952). 5. J. A. Swift, Proceedings of the 8th International Hair Science Symposium of the DWI, Kiel, Germany, September 9-11, 1992.