EMOLLIENT ACTION OF KUKUI NUT OIL 247 Our data also exclude skin penetration as an explanation. Oils made of lipids containing saturated fatty acids are reputed to have a greasy feel because they are reputed to remain on top of the skin. We used coconut oil as such an example. Our skin stripping data did not confirm this reputation because coconut oil penetrated the stratum corneum essen- tially as well as kukui oil. We therefore conclude that skin penetration is not the reason kukui oil has a different skin feel compared with oils containing primarily saturated fatty acids. We can speculate as to why kukui oil either neat or as a lotion feels like an excellent emollient, taking into account reviews by Rieger (7) and Idson (8). We know that kukui oil penetrates deeply into the stratum corneum. It would lay down a triglyceride blanket of lipids containing both saturated and unsaturated fatty acids. Such blankets should be semipermeable (9) with regard to TEWL. This blanket would protect the skin from further drying yet would allow some water to escape, inducing the skin to heal natu- rally. We can speculate further as to the use of kukui oil by the ancient Hawaiians on newborns. The skin senses the rate of TEWL and biosynthesizes a protective lipid layer that is responsive to the humidity of the environment. A child in utero would tend to have skin that is adapted to 100% humidity. After birth, the baby's skin would therefore be extremely susceptible to chapping as the relative humidity would probably be considerably less than 100%. Kukui oil would have provided a semipermeable barrier that would have protected the skin of newborns from further chapping and would have allowed their skin to adjust to the new environment. ACKNOWLEDGMENTS We wish to thank Mathew Pania for determining peroxide values and Christopher Ako for helping to develop skin stripping fatty acid analyses. This work was supported by the Governor's Agriculture Coordinating Committee Contract #91-34 and is Journal Series #3773 of the Hawaii Institute of Tropical Agriculture and Human Resources. REFERENCES (1) G. O. Burr and M. M. Burr, On the nature and role of the fatty acids essential in nutrition, J. Bid. Chem., 86, 587-621 (1930). (2) J. T. Goodgame, S. F. Lowry, and M. F. Brennan, Essential fatty acid deficiency in total parenteral nutrition: Time course of development and suggestions for therapy, Surgery, 84, 271-277 (1978). (3) G. Grubauer, P.M. Elias, and K. R. Feingold, Transepidermal water loss: The signal for recovery of barrier structure and function, J. Lip. Res., 30, 323-333 (1989). (4) C. S. Tamaru, H. Ako, and C.-S. Lee, Fatty acid and amino acid profiles of spawned eggs of striped mullet, Mugil cephalus L, Aquaculture, 105, 83-94 (1992). (5) J. Brod, H. Traitler, A. Studer, and O. De Lacharriere, Evolution oflipid composition in skin treated with blackcurrant seed oil, Int. J. Cosmet. Sci., 10, 149-159 (1988). (6) G. R. Goss, D. D. Brooks, S. K. Brophy, and B. L. Hayden, A comparative study of soybean oil oxidation methodology, Presentation at the 1989 AOCS Convention, Cincinnati, Ohio. (7) M. Rieger, Skin care: New concepts vs established practices, Cosmet. Toiletr., 106, 55-68 (1991). (8) B. Idson, Dry skin, moisturizing and emolliency, Cosmet. Toiletr., 107, 69-78 (1992). (9) V. K. LaMer, Ed., Retardation of Evaporation by Monolayers: Transport Processes (Academic Press, New York, 1962).

j. Soc. Cosmet. Chem., 44, 249-261 (September/October 1993) Direct measurement of moisture in skin by NIR spectroscopy KATHLEEN A. MARTIN, Helene Curtis, Inc., 4401 W. North Avenue, Chicago, IL 60639. Received March 23, 1993. Synopsis A method to directly determine water content in skin as well as the nature of water binding using near-infrared reflectance spectroscopy is introduced. The method is able to quantirate water on a relative basis and to distinguish free, bulk, and bound water. In addition, scattering of near-infrared radiation off the skin surface can be used as a measure of skin smoothness. As examples of the method's potential, effects of both humidity and moisturizer application on moisture content, water type, and scattering effects have been studied on dry legs. INTRODUCTION According to Kligman (1), skin characterized as dry is not necessarily lacking in mois- ture but is more often considered to have a rough, uneven surface that scatters light efficiently, leading to a dry, matte appearance. Normal dry skin can be caused by climate, cleansing, age, or heredity. The function of a moisturizing product is to retard water loss by creating a barrier to surface evaporation, to create a smoother, softer feel to the skin, and to improve the appearance of the skin. The outermost layer of skin is the stratum corneum (SC), about 10-20 microns thick and composed of partially dehydrated cells in a lipid matrix. It is this layer that is considered to be responsible for the barrier function of skin. Below the SC is the epidermis, about 100-200 microns thick, and below that the dermis, about 2-4 mm thick. Skin becomes increasingly more hydrated at the deeper layers. Obata and Tagami indicate that the main role of water in the stratum corneum is to control softness and pliability (2). Several studies on the effect of humidity on both the strength and number of water-binding sites in the SC have been performed and are summarized by Potts (3). Generally, increasing relative humidity causes an increase in tissue hydration, the rate of hydration being greater at higher relative humidity. The nature of water in the SC was concluded to be different at different relative humidities. Using NMR and IR, Hansen and Yellin (4) determined that at a water content of below 10% the water present was tightly bound, presumably to the polar sites of the proteins. At water contents between 10% and 40%, they found less tightly bound water, which 249