Design and Evaluation of Activated Charcoal-Enriched Antibacterial Soap Using a Design of Experiments (DoE) Approach

Background: The formulation and optimization of an activated charcoal-based antibacterial soap were investigated to enhance cleansing efficacy and antimicrobial properties. The study was conducted at Chalapathi Institute of Pharmaceutical Sciences, Guntur, from 06 April 2024 to 31 January 2025, using a Box-Behnken Design (BBD) to optimize key formulation parameters. Materials and Methods: Activated charcoal and coconut oil were used as primary ingredients, with sodium hydroxide, Sodium Lauryl Sulfate (SLS), and stearic acid to improve lathering and hardness. BBD analyzed the impact of activated charcoal, SLS, and stearic acid concentrations on foam retention time and hardness. Statistical methods, including ANOVA and interaction profiling, were used. Physicochemical properties such as moisture content, free alkali, foam height, viscosity, pH, and Total Fatty Matter (TFM) were evaluated. Antimicrobial activity against Bacillus subtilis and Escherichia coli was determined using Minimum Inhibitory Concentration (MIC) and Minimum Bactericidal Concentration (MBC). Patch testing confirmed dermatological safety. Results: The optimized soap exhibited 12.5% moisture content, 18% alcohol-insoluble matter, 2% free alkali, 13 cm foam height, 2500 cP viscosity, 82% TFM, and pH 6.1. Hardness was 62.78 N. MIC values were 50 μg/mL for E. coli and 25 μg/mL for B. subtilis, with significant bactericidal activity. No skin irritation was observed. Conclusion: The study successfully developed an antibacterial soap with optimized physicochemical properties, promising antimicrobial efficacy, and excellent skin compatibility, making it a potential candidate for personal care applications.