Ag nanoparticles as a safe preservative for use in cosmetics

Concern is continuously raised regarding the safety of preservatives, which are crucial in most cosmetic preparations. The antimicrobial effects of silver (Ag) are well recognized; however, Ag has some limitations as a preservative, such as its interference with salts. In this study, we investigated the effects of recently synthesized Ag nanoparticles on microorganisms, the permeability of Ag nanoparticles in human skin, and the cytotoxicity of Ag nanoparticles in human keratinocytes under UVB-irradiation. Ag nanoparticles were found to be very stable, and they did not exhibit sedimentation for over one year. Ag nanoparticles showed sufficient preservation efficacy against mixed bacteria and mixed fungi, and did not penetrate normal human skin. At concentrations of 0.002 ppm~0.02 ppm, Ag nanoparticles had no effect on HaCaT keratinocytes, and did not enhance UVB-induced cell death. These results suggest that Ag nanoparticles are suitable for use as a preservative in cosmetics.