Applications of microemulsions in cosmetics.

Since microemulsions were discovered approximately six decades ago, their applications in several fields, including cosmetics, have been increased due to their good appearance, thermodynamic stability, high solubilization power, and ease of preparation. In addition, microemulsions can enhance skin permeation of the loaded substances. They are classified into three types: oil-in-water, bicontinuous, and water-in-oil. All types of microemulsions can be formed spontaneously when the ratios of oil, water, and amphiphile in the systems are appropriate. These proper ratios can be found in a microemulsion region of a phase diagram. The efficiency of microemulsions in topical application is related to microemulsion type. Microemulsion characterization needs a combination of the data from several experimental techniques. Numerous applications of cosmetic microemulsions include skin-care, hair-care, and personal-care products for improving the product efficiency and stability. Moreover, new materials have been developed to be used in cosmetic microemulsion formulations for increasing the product efficiency and reducing the toxicity. The aim of this review is to present some basic information of microemulsions and novel applications of microemulsions in cosmetic formulations.