Evaluation of hair growth properties of glycyrrhizic acid

Background: Many studies have indicated that hair growth and color regulation are cyclical processes involved in the strict regulation of multiple signaling pathways, such as the transforming growth factor and Wnt/β-catenin protein pathways. It has also been reported that Glycyrrhiza uralensis extract can promote hair growth, but its active components are still unclear. Objectives: The aim of this study was to investigate the potential hair blackening effect and mechanisms of glycyrrhetic acid (GA) extracted from Glycyrrhiza uralensis. Materials and Methods: Different concentrations of GA solution (1.0 wt%, 10.0 wt%, and 20.0 wt%) were coated onto the skin surface of fur model mice induced by H₂O₂ for two weeks. After that, the number and depth of follicles and cortex thickness were observed in the skin tissue stained by hematoxylin and eosin (H&E). The relative mRNA levels of β-catenin, vascular endothelial growth factor (VEGF), and tyrosinase in skin tissue were analyzed using quantitative real-time polymerase chain reaction. The protein levels of β-catenin, VEGF, and tyrosinase were also evaluated by western blotting and immunohistochemistry. Results: There was a marked increase in the number of hair follicles and the blackening effect upon exposure to 10.0 wt% and 20.0 wt% GA. Moreover, the β-catenin, VEGF, and tyrosinase expression levels in the skin tissue varied significantly compared to those in the model group. Conclusion: GA showed positive effects on hair growth factor expression levels in mice, which meant that GA could promote hair blackening.