In a comprehensive study carried out by Yokota, T. et al., the inhibitory effects of glabridin on melanogenesis as well as inflammation were examined. The structure-function relationship of glabridin was also studied. Topical skin-depigmentation activities of the active component, glabridin, were examined using UVB-induced pigmented skins of brownish guinea pigs. A 0.5% glabridin solution was applied topically to the skin. Topical application of glabridin significantly reduced pigmentation induced by UVB radiation on the backs of the brownish guinea pigs. Skin samples were also taken from each of the glabridin treated areas for histological studies. The treated tissue was stained with 0.1% DOPA and the inhibition of melanogenesis was evaluated by counting the number of DOPA-positive melanocytes/mm2 under an optical microscope. Epidermal histological studies performed showed that DOPA-positive melanocytes reduced in number on the skin treated with glabridin. Treatment with glabridin also lightened the skin colordue to inhibition of melanogenesis. The authors concluded that the glabridin present in Licorice roots inhibits both melanin synthesis and inflammation. They also observed that these properties of glabridin were related to its structure.
