Stability evaluation of nano loaded and conventional soaps and ointments

Abstract

This study evaluates the 12-month stability of conventional and nano loaded soap and ointment formulations, focusing on physicochemical and microbiological parameters. The nano loaded products incorporate silver (Ag), copper (Cu), and zinc (Zn) nanoparticles, known for their antioxidant, photoprotective, and antimicrobial properties. Over the storage period, the nano loaded soap consistently maintained a white, smooth, and clear appearance with minimal loss in surfactant and moisturizer content, stable pH, and significantly reduced microbial growth (< 10 CFU/g). In contrast, the conventional soap exhibited discoloration, viscosity loss, and a microbial count exceeding 10⁴ CFU/g by the twelfth month. Similarly, the nano loaded ointment retained its homogeneity, pH, viscosity, and softening point, showing no phase separation or microbial contamination. The conventional ointment, however, showed signs of degradation, including clumping, oil sweating, and microbial proliferation beyond safety thresholds. These findings highlight the multifunctional role of metal nanoparticles in stabilizing formulations by preserving their physical structure, chemical composition, and microbiological safety. The results affirm the superior shelf-life performance and safety of nano loaded topical products and support their continued development for cosmetic and therapeutic applications.