Comparative studies on tyrosinase inhibitory activities of aqueous and ethanolic extracts of cosmetic whitening traditional Chinese medicines

OBJECTIVE: "Eight White Herbal Powders" documented in "The Secret Formula in Lu's House" is a well-known cosmetic whitening prescription in ancient China. This study aimed to investigate (a) the tyrosinase inhibitory activity of the aqueous extracts of individual herbs in this formula and (b) the feasibility of utilizing 80% ethanol as an alternative extraction medium for the whitening components of the herbs. METHODS: The aqueous extracts of individual herbs were tested for tyrosinase inhibitory effects, using kojic acid as the positive control. Comparative activity analysis was done between the aqueous and the 80% ethanol extracts for three selected herbs. RESULTS: Bailian showed the highest tyrosinase inhibitory activity, followed by Baizhi and Baiji. However, compared with the aqueous extracts, the 80% ethanol extracts of the three herbs displayed significantly lower tyrosinase inhibitory effects, as evidenced by their substantially larger IC₅₀ values (by ∼ 5.9 ∼ 23 times). CONCLUSION: By comparison of the tyrosinase inhibitory activities of the extracts, water appeared to be a better extraction medium than 80% ethanol for the whitening constituents in Bailian, Baizhi and Baiji.