Using hair growth activity, physical stability, and safety tests to study hair tonics containing ethanol extract of licorice (Glycyrrhiza glabra Linn.)

Objective: The purpose of this study was to determine the safety, physical stability, and hair growth activity of ethanol extract of licorice. Methods: In this study, 2.5%, 5%, and 10% licorice extract was formulated into a hair tonic as a tonic is easier to use and is not sticky like a semisolid dosage. The hair growth activity test was conducted by rubbing the hair tonic preparations on rabbit’s backs; subsequently, the hair length, hair thickness, hair weight, and hair density were measured. Quantitative analysis of glycyrrhizic acid from the licorice ethanol extract with a ultraviolet spectrophotometer showed a level of about 156.65 mg/g or 15.665%. The physical stability test was performed on samples of the tonic stored at low (4±2°C), room (25±2°C), and high (40±2°C) temperature, and a cycling test was also performed. The safety test was performed using an eye irritation test that employed the Hen’s egg test–chorioallantoic membrane (HET-CAM) method and a skin irritation test that employed the patch test method. Results: The hair tonics containing 5% and 10% licorice extract had an equivalent activity of hair growth and even better than the positive control containing 2% minoxidil. The physical stability test showed that the licorice extract hair tonic has good physical stability. The results of the safety test showed no skin irritation, whereas the HET-CAM test showed that the hair tonic containing licorice extract showed mild eye irritation. Conclusions: Licorice ethanol extract hair tonic solutions in concentrations of 2.5%, 5%, and 10% had hair growth activity similar to that of the positive control (minoxidil). They have a good physical and chemical stability, also safe for topical use, except the 2.5% licorice ethanol extract hair tonic solution which caused mild eye irritation.