Antimicrobial efficacy of selected natural preservatives in a cosmetic emulsion

Microbiological quality of cosmetic products is a significant issue for the cosmetic industry in terms of the excessive contamination [1] and contact allergies caused by cosmetic preservatives [2]. The term 'natural preservative' has evoked great interest in recent years in consumers, marketing and research. It is not an officially defined term, but rather a reflection of a broader concept of the so-called natural cosmetics presented by different certification standards. As data on the antimicrobial efficacy of natural preservatives are scarce, the aim of the present study was to investigate 13 preservatives (11 accepted as natural and 2 conventional preservatives as controls) at 2 concentrations in an o/w cosmetic emulsion.

The total aerobic bacterial count and total combined yeast count (analysed according to the European Pharmacopoeia 8.0) were below the acceptable limit for all formulations. Challenge tests were performed according to the ISO 11930 standard. The criterion A was fulfilled by p-anisic, benzoic, dehydroacetic, salicylic and sorbic acid, dehydroacetic acid/benzyl alcohol, glyceryl caprylate and ethanol. Grapefruit seed extract was efficient only at a higher concentration, while levulinic acid and Lactobacillus ferment failed to protect the formulation. Phenoxyethanol and methylparaben/propylparaben were inefficient at minimum concentrations.

The results offer important comparative data on the level of antimicrobial protection within the group of natural preservatives and in reference to some typical, widely used conventional preservatives. Moreover, further research must be encouraged with regard to cosmetic over-preservation.

[1] Lundov MD, Zachariae C. Int J Cosmet Sci 2008; 30:471 – 474.

[2] Schwensen JF, White IR, Thyssen JP, Menne T, Johansen JD. 2015; 73:133 – 141.