Nanoemulsion: process selection and application in cosmetics--a review.

In recent decades, considerable and continuous growth in consumer demand in the cosmetics field has spurred the development of sophisticated formulations, aiming at high performance, attractive appearance, sensorial benefit and safety. Yet despite increasing demand from consumers, the formulator faces certain restrictions regarding the optimum equilibrium between the active compound concentration and the formulation base taking into account the nature of the skin structure, mainly concerning to the ideal penetration of the active compound, due to the natural skin barrier. Emulsion is a mixture of two immiscible phases, and the interest in nanoscale emulsion has been growing considerably in recent decades due to its specific attributes such as high stability, attractive appearance and drug delivery properties; therefore, performance is expected to improve using a lipid-based nanocarrier. Nanoemulsions are generated by different approaches: the so-called high-energy and low-energy methods. The global overview of these mechanisms and different alternatives for each method are presented in this paper, along with their benefits and drawbacks. As a cosmetics formulation is reflected in product delivery to consumers, nanoemulsion development with prospects for large-scale production is one of the key attributes in the method selection process. Thus, the aim of this review was to highlight the main high- and low-energy methods applicable in cosmetics and dermatological product development, their specificities, recent research on these methods in the cosmetics and consideration for the process selection optimization. The specific process with regard to inorganic nanoparticles, polymer nanoparticles and nanocapsule formulation is not considered in this paper.