EMOLLIENT ACTION OF KUKUI NUT OIL

SYNOPSIS
Dry skin drives the search for effective emollients. This report searches for an explanation of the superb skin feel and healing properties of this native Hawaiian oil. Using skin stripping technology and gas chromatography, we demonstrated kukui nut oil's ability to penetrate the stratum corneum, leaving a triglyceride barrier containing a mixture of saturated and unsaturated fatty acids. A kukui oil-based lotion was also very effective in laying down an emollient layer of lipids. It is speculated that the superior skin feel of kukui oil is due to the fact that it lays down a mixture of saturated and unsaturated fatty acids, forming a semipermeable barrier that would protect the skin from further drying and would allow dry skin to heal naturally. This would also explain its beneficial effect on the symptoms of psoriasis.

Kukui oil does not cure psoriasis, eczema or dry skin, but it does provide effective treatment for the symptoms. The pure oil softens the scales, and provides lipids that are quickly absorbed by the skin. These lipids slow water loss through the skin.

INTRODUCTION
Kukui nut oil is produced in Hawaii by expeller pressing the oil from the nut of the kukui tree (Aleurites moluccana). Hundreds of years ago, Hawaiians used it to protect the skin of babies. It is used as a body oil by modern-day Pacific Islanders. Kukui oil forms a semipermeable barrier that protects dry skin from further damage and permits dry skin to heal naturally.

While the definition of dry skin is beyond the scope of this paper, it may be assumed that dry skin is characterized by apparent dryness, scaling, cracking, etc. These conditions may be induced by the loss of natural lipids in the stratum corneum.

Household chemicals such as soaps, or extreme exposure to the wind, sun, and sea such as occurs commonly in Hawaii, may also cause dry skin. The same condition is often reported by people who live in very cold environments (where barrier lipid fluidity may be inappropriate to prevent water loss through the skin) or very dry environments (where water loss would be extremely high).

Normal dry skin heals naturally. Unless further damage occurs, barrier function is restored to dry skin within 48 hours. We propose that lipids composed of a mixture of saturated and unsaturated fatty acids, as in kukui oil, provide a protective barrier against excessive trans epidermal water loss and promote healing. Kukui oil contains 8.1% saturated fatty acids, 15.3% monounsaturated fatty acids, 43% linoleate (C18:2n-6, a diunsaturated fatty acid), and 33% linolenate (C18:3n-3, a triunsaturated fatty acid).

DISCUSSION
We are lukewarm about dry skin being caused primarily by a localized essential fatty acid deficiency in omega 6 fatty acids. Our data also exclude skin penetration as an explanation.

We conclude that skin penetration is not the reason kukui oil has a different skin feel compared with oils containing primarily saturated fatty acids. 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. This blanket would protect the skin from further drying yet would allow some water to escape, inducing the skin to heal naturally.

We can speculate further as to the use of kukui oil by the ancient Hawaiians on newborns. The skin senses the rate to 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.

The use of kukui nut oil to treat psoriasis is as yet, anecdotal. However, the ability of this oil to penetrate the stratum corneum and and its outstanding emollient properties easily explain why this oil helps with the symptoms of psoriasis.

*JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS (September/October 1993) by H. Ako, L. Fujikawa and D. Gray, Department of Environmental Biochemistry, University of Hawaii (Harry Ako, Ph.D.) and Oils of Aloha, (Dana Gray).

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