Formulation and stability evaluation of a cosmetics emulsion loaded with different concentrations of synthetic and natural preservative

Abstract

Essential oils are currently the topic of extensive scientific research, and their potential as active pharmacological chemicals or natural preservatives has attracted the attention of the cosmetic and pharmaceutical industries. Modern cosmetics, with their complex compositions, watery formulations, and direct contact with bacterial skin flora, provide excellent habitat for microbe growth. The use of preservatives is required due to the significant danger of contamination and, as a result, a risk to customers' health. The aim of the study was to formulate and subsequently evaluate the stability of a cosmetic emulsion based on different concentrations of synthetic and natural preservatives. We have performed a cosmetic emulsion base with triethanolamine as an emulsifier. Four samples were prepared using the formulation base and a synthetic preservative, methylparaben, in concentrations 0.2% and 0.3%, and a natural preservative, lemongrass essential oil, in concentrations, 1%, and 2%. The samples were stored for 4 weeks in room conditions. They were evaluated immediately after preparation and for four weeks related to smell, color, odor, consistency, homogeneity, pH, phase separation, viscosity changes and microbial growth. After two weeks, there was a phase separation in two formulations with methylparaben. After four weeks, other formulations were stable in odor, appearance, color, homogeneity. The essential oils didn’t significantly affect the pH values of the formulation, it was in the recommended range. Adding the essential oil affected the viscosity of the formulation base, and the more the concentration of essential oil was more the viscosity of the formulation lowered. The emulsions formulated with lemongrass essential oil had no microbial and fungal growth, so the self-preserving effect was demonstrated. We concluded that cosmetic emulsion entrapped with lemongrass essential oil in a concentration of 1% showed promising stability, physicochemical characteristics and self-preserving effect in room storage conditions.