Researchers at cosmetics company Kao have demonstrated that a eucalyptus extract has the ability to improve the skin function on the outer layer in dry skin by increasing ceramide levels in the stratum corneum, in the epidermis and in keratinocytes.
The scientists from the Japanese firm found the plant extract may have a therapeutic effect on dry skin by increasing its content of ceramide (lipid molecules), and improving its water-holding and barrier functions.
The study and the results were published in the International Journal of Cosmetic Science.
“These results indicate that the ceramide increase in keratinocytes elicited by the eucalyptus extract plays an important role in recovering stratum corneum dysfunctions and that may underlie the therapeutic effects of the eucalyptus extract,” noted the researchers.
The aim of the study for the Japanese researchers was to identify a plant extract that would improve stratum corneum functions and to highlight the mechanisms involved.
Based on the previous information that the skin’s outer layer functions depend on the level of ceramide in the stratum corneum, the researchers identified a eucalyptus extract that elicited the desired effects.
Their tests demonstrated that the addition of the plant extract to the skin’s outer layer cells in culture increased the level of ceramide in a dose-dependent manner and also increased the biosynthesis of ceramide, glucosylceramide and sphingomyelin.
Topical application of the eucalyptus extract on the dry skin of human subjects induced by acetone and diethylether treatment resulted in a significant increase in ceramide level in the stratum corneum, a significant improvement in its water-holding function and an improvement in its barrier function.
This holds key implications for further use in topical skin creams or formulas.
Furthermore, the addition of one of the main components of the eucalyptus extract, macrocarpal A, to human keratinocytes in culture increased the level of ceramide and showed it is the key component that stimulates the synthesis of ceramide in the stratum corneum.
Clinical tests were also carried out with the aid of eighteen healthy subjects. Two skin sites were chosen on the inner forearm of each subject which was then treated with acetone/diethylether for 30 min to induce dry skin.
The subjects were asked to treat the acetone/diethylether-treated skin sites either with lotion containing one per cent eucalyptus extract or with lotion containing only the vehicle for four days.
The skin sites were measured after the dry skin was induced and after the four day treatment by a tape stripping method.
Ishikawa, J., Shimotoyodome, Y., Chen, S., Ohkubo, K., Takagi, Y., Fujimura, T., Kitahara, T. and Takema, Y. (2012), ‘Eucalyptus increases ceramide levels in keratinocytes and improves stratum corneum function.’ International Journal of Cosmetic Science, 34: 17–22. doi: 10.1111/j.1468-2494.2011.00675.x