A review on green nanoemulsions for cosmetic applications with special emphasis on microbial surfactants as impending emulsifying agents

摘要

Abstract Nanoemulsions are being increasingly utilized in the pharmaceutical, cosmetics, and food industries. They have gained special attention in the cosmetic sector owing to their smaller size and higher kinetic stability and their ability to improve the cutaneous penetration of active ingredients. In addition, they reduce transepidermal water loss, which augments the skin's barrier function. In recent years, the increased awareness among consumers about the health‐linked benefits of natural ingredients in cosmetics has urged finding green cosmetic ingredients that are benign to the skin. One of the natural motivations for this quest is finding suitable emulsifier candidates with negligible side effects that are sourced from plants or microbes, which can serve as viable replacements to the erstwhile used synthetic surfactants. Formulating a stable nanoemulsion system for cosmetic application entails a systematic understanding of important attributes of the surfactant candidate such as critical micelle concentration, hydrophilic lipophilic balance, critical packing parameter, and Winsor ratio that are pivotal to the overall performance of the emulsion system. The current review attempts to portray the salient features of nanoemulsion systems in cosmetic formulations, by essentially capturing the important characteristics of the emulsifier that dictate the overall stability of a nanoemulsion system. The recent transition toward the use of green ingredients such as emulsifiers and oils that are dermatologically safe has been delineated, by highlighting their important properties. Furthermore, the progress made so far in the application of microbial biosurfactants in nanoemulsion formulations is presented. Finally, the factors that dictate the overall stability of the nanoemulsion are briefly reviewed.