Formulation and Evaluation of a Natural Herbal Soap from Noni (Morinda Citrifolia) and Lemon (Citrus Limon): Synergistic Effects on Skin Compatibility and Antimicrobial Efficacy

Abstract

The growing demand for safe, effective, and eco-friendly skincare alternatives has spurred interest in plant-based formulations. Noni (Morinda citrifolia) and Lemon (Citrus limon) possess documented bioactive properties beneficial for skin health, but their combined application in soap remains underexplored. This study aimed to formulate, characterize, and evaluate herbal soaps from Noni extract and Lemon juice to determine their suitability as natural skincare products. Three soap batches were produced via cold-process saponification with varying Noni:Lemon ratios (N90/L10, N80/L20, N70/L30). Physicochemical properties (pH, moisture content, total fatty matter, foam stability) and antimicrobial efficacy (against Staphylococcus aureus, Escherichia coli, and Pseudomonas aeruginosa) were assessed using standard laboratory protocols. A controlled laboratory experiment coupled with a consumer trial involving 30 adult consumers was conducted, while 28 dermatologists provided independent expert assessments of skin compatibility and product safety. All formulations met standard quality benchmarks. The N80/L20 soap demonstrated superior broad-spectrum antimicrobial activity, with the lowest Minimum Inhibitory Concentration (MIC) values. Consumer evaluation revealed the N80/L20 formulation as optimal, receiving the highest scores for gentleness (4.2/5), moisture retention (4.4/5), and overall skin compatibility (4.4/5). It was the most preferred for long-term use (70%) and generated the fewest adverse skin reactions. Statistical analysis confirmed a significant difference in suitability between formulations (Repeated Measures ANOVA, F=9.87, p=0.0002), with N80/L20 being significantly superior. The 80:20 ratio of Noni to Lemon juice produces a soap with an ideal balance of antimicrobial potency, skin-friendliness, and user acceptance. This study validates the synergistic potential of these botanicals, offering a promising, natural, and multifunctional alternative to conventional skincare cleansers.