Abstract
Preservation using combinations of antibacterial molecules has several advantages, such as reducing the level of usage and broadening their antimicrobial spectrum. More specifically, the use of quaternary ammonium surfactants (QAS)—which are profusely used in hair care products and some are known as efficient antimicrobial agents—is limited due to some potential cytotoxicity concerns. This study shows that the concentration of some widely used cosmetic preservatives can be decreased when combined with very small quantities of QAS, i.e., Polyquaternium-80 (P-80) and/or Didecyldimethylammonium chloride (DDAC). The antimicrobial activity of their mixtures was first evaluated by determining the minimum inhibitory concentration (MIC) before and after the addition of QAS. Following up on this finding and targeting an ultimate consumer friendly antimicrobial blend, yet with optimal safety, we chose to utilize the food-grade preservative Maltol as the main natural origin antimicrobial agent mixed with minimum concentrations of QAS to improve its moderate antimicrobial properties. The preservatives were tested for MIC values, challenge tests and synergy using the fractional inhibitory concentration index (FICI). The antimicrobial efficacy of Maltol was found to be synergistically improved by introducing catalytic amounts of P-80 and/or DDAC.
Highlights
Surfactants are the core compounds of cosmetic formulations and contribute to a wide range of roles [1,2]
Surfactants play a key role in the performance of solubilization and deposition systems used to deliver active molecules onto the hair, scalp and skin [3]
Cationic surfactants are used for quite different purposes than the anionic surfactants, since they are not effective as anionic detergent in cleansing systems
Summary
Surfactants are the core compounds of cosmetic formulations and contribute to a wide range of roles [1,2]. At pH above the isoelectric point of hair, i.e., pH 3.67, the cationic surfactants bind to the negative charges on the hair’s keratin with their cationic heads close to the negatively charged sites on the fiber surface and their hydrophobic tail oriented away from the fiber. This results in a hydrophobic coating of the fiber, which is soft and easy to comb [5,6]
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