Risk-Based Assessment of Cosmetic Preservation Using Raw-Material-Associated Microorganisms in an Adapted EN ISO 11930 Challenge Test

Cosmetic formulations containing natural or minimally processed raw materials are prone to microbial contamination, which can compromise product safety and quality. The standard ISO 11930 preservation challenge test employs a predefined set of test microorganisms, which may not adequately represent product-associated contaminants. In the present study, an adapted ISO 11930 preservation challenge test was applied to compare the antimicrobial performance of four preservative systems in an oil-in-water cosmetic formulation. In addition to the five standard reference strains, seven environmental and raw-material-associated microorganisms associated with walnut and apricot kernel shells were included. All preservative-containing formulations fulfilled the required acceptance criteria; however, marked differences in time-dependent antimicrobial activity were observed between preservative systems. Among the tested systems, the formulation containing 0.4% potassium sorbate demonstrated the most rapid and broad-spectrum antimicrobial performance across the expanded microbial panel. In contrast, combinations of potassium sorbate with sodium benzoate and benzyl alcohol showed slower antimicrobial efficacy. In conclusion, this study demonstrates that reliance solely on standard reference microorganisms may underestimate preservation risks in cosmetics that use naturally derived raw materials. The adaptive preservation challenge test is a risk assessment approach for evaluating the microbiological stability of cosmetic formulations with reduced-preservative systems.