OBJECTIVE To study regularity of different components whose skin permeability is enhanced by essential oils (EOs) from traditional Chinese medicine (TCM) with hot property.

METHODS Five EOs from TCM with hot property, namely Galangal oil, Dried Ginger oil, Cinnamon oil, Pepper oil, and Evodia oil were prepared and used in further studies. The in vitro skin cytotoxicity of these EOs and chemical penetration enhancer (PE) Azone were compared. HPLC method was established to determine 9 TCM components that are usually used in permeation studies. And the in vitro permeation experiments were carried out using the modified Franz diffusion cell method to evaluate the penetration enhancement effects of five EOs.

RESULTS The cytotoxicity test revealed the IC₅₀ value of EOs was 3.63-8.15 times of that of Azone, the classical chemical PE. HPLC method showed perfect specificity and 9 TCM components performed well in linear relationship, precision, repeatability, stability, and average recovery rate. The results of multiple linear regression showed a significant association between the penetration enhancement effects of EOs from TCM with hot property and logP values of the TCM components. EOs from TCM with hot property showed satisfactory penetration enhancement effects for hydrophobic components with logP values in the range of 2.6-3.5, e.g. resveratrol, tetrahydropalmatine and quercetin.

CONCLUSION EOs from TCM with hot property should be reasonably selected as PE according to the oil-water partition coefficient of the ingredients.