246 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS Table II Fatty Acids in Strippings From Three Individuals • Subject A Subject B Subject C C 12 Laurate 7 1 16 C14 Myristate 6 10 10 Unknown 5 -- -- C16 Palmirate 20 24 35 C 16:ln-7 Palmitoleate 4 10 4 C 18 Stearate 8 5 21 C18:ln-90leate 23 14 7 C 18:2n-6 Linoleate 16 2 6 C 18:3n-3 Linolenate 13 __b 2 C18:4n-30ctadecatetraenoate -- 3 -- C20:ln-9 Eicosenoate -- 5 -- C20:4n-6 Arachidonate -- 3 -- C20:5n-3 Eicosapentaenoate Trace 11 -- C22:6n-3 Docosahexaenoate Trace 9 -- Total fatty acids 100 100 100 For each individual, all five strippings were summed. Data are expressed as percentages of total fatty acids. Not detected. DISCUSSION Kukui oil has a reputation for going rancid quickly. We chose to focus our efforts on linolenate (C18:3n-3) because it is the most unstable of the fatty acids in kukui oil. Disappearance of linolenate would be a worst-case scenario. The sensitivity of linolenate was confirmed by the fact that of the samples that did go rancid, linolenate with three double bonds disappeared far faster than linoleate with two double bonds (C 18:2n-6) or oleate with one double bond (C18: ln-9). Saturated fatty acids were stable. This said, kukui oil has an undeserved reputation for turning rancid quickly. Kukui oil is stable for three to five months, and work is in progress to stabilize it further. Brod et al. (6) noted the non-equivalence of one day at 60øC and 22 days at room temperature. We also observed this non-equivalence. In our 60øC tests, we found little if any linolenate degradation in 17 days, which is equivalent to about one year at room temperature. This was not consistent with the room temperature tests. Also, our 60øC test samples, which were approximately 90% intact based on fatty acid analyses, had very high peroxide values. This points out the problematic nature of molecular-level interpretations of peroxide value tests with kukui oil. The skin stripping method of Brod et al. (5) worked well for us. The data seemed quantitative and internally consistent. Control strippings showing the effect of diet on the skin fatty acid profile may be worth further investigation. They raise a question of whether non-clinical variations in skin fatty acid profiles affect skin properties. We began this paper by wondering why kukui oil has its reputedly excellent emollient properties. On nutritional grounds, we decided to be lukewarm about metabolic ex- planations. We are lukewarm about dry skin being caused primarily by a localized essential fatty acid deficiency in omega 6 fatty acids. This being the case, we are lukewarm about the superiority of gamma linolenate (C18:3n-6), such as found in blackcurrant oil, over the alpha form.

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).