Low-level efficacy of cosmetic preservatives

Area of Science:

• Cosmetic Science
• Microbiology
• Dermatology

Background:

• Cosmetic preservation often relies on multiple preservatives to ensure broad-spectrum antimicrobial activity.
• Some commonly used cosmetic preservatives are also known allergens, necessitating careful formulation to minimize adverse reactions.
• Phenoxyethanol is a widely used preservative, but its efficacy can be enhanced when combined with other agents.

Purpose of the Study:

• To evaluate the antimicrobial efficacy of cosmetic preservatives, including known allergens, alone and in combination.
• To determine if combining preservatives, particularly phenoxyethanol with allergenic preservatives, allows for reduced concentrations while maintaining preservation.
• To assess the synergistic or additive effects of preservative combinations on microbial growth in a cosmetic formulation.

Main Methods:

• Minimum Inhibitory Concentration (MIC) and Fractional Inhibitory Concentration (FIC) were determined for diazolidinyl urea, MCI/MI, MI, and phenoxyethanol against Staphylococcus aureus, Pseudomonas aeruginosa, Candida albicans, and Aspergillus niger.
• Challenge tests were conducted on a cosmetic cream using various concentrations and combinations of these preservatives.
• Antimicrobial activity and potential interactions between preservatives were analyzed.

Main Results:

• MCI/MI demonstrated the lowest MIC against all tested microorganisms.
• Combinations of preservatives showed additive effects, with no observed antagonistic interactions.
• Phenoxyethanol combined with diazolidinyl urea, MCI/MI, or MI effectively preserved a cosmetic cream at concentrations significantly lower than individual MICs and maximum permitted levels.

Conclusions:

• Combining phenoxyethanol with allergenic preservatives like diazolidinyl urea, MCI/MI, or MI enhances antimicrobial efficacy.
• This strategy allows for a marked reduction in the concentration of allergenic preservatives in cosmetic formulations.
• Optimized preservative combinations offer a viable approach to achieve effective cosmetic preservation while minimizing exposure to high concentrations of potential allergens.