Nanoemulsions: Preparation Techniques and Pharmaceutical Applications – A Comprehensive Review

Nanoemulsions (NEs) are advanced colloidal drug delivery systems consisting of nanosized droplets of one immiscible liquid dispersed within another liquid phase and stabilized using surfactants and co-surfactants. Due to their small droplet size (approximately 20–200 nm), large interfacial area, improved kinetic stability, enhanced solubilization capacity, and ability to protect encapsulated molecules, nanoemulsions have gained considerable importance in pharmaceutical research. Poor aqueous solubility and limited bioavailability remain major challenges for many therapeutic agents, particularly Biopharmaceutical Classification System (BCS) class II and IV drugs. Nanoemulsion-based systems provide an effective approach to overcome these limitations by improving dissolution rate, permeability, absorption, and therapeutic performance. Nanoemulsions can be prepared using high-energy approaches such as high-pressure homogenization, ultrasonication, and microfluidization, or low-energy approaches including spontaneous emulsification, phase inversion temperature, and phase inversion composition methods. The selection of preparation technique depends on formulation composition, desired droplet characteristics, drug stability, and scalability requirements. This review focuses on the formulation principles, preparation techniques, characterization parameters, and pharmaceutical applications of nanoemulsions. Particular emphasis is placed on oral, topical, ocular, parenteral, pulmonary, nasal, anticancer, antimicrobial, and targeted drug delivery applications. The potential of nanoemulsions as versatile carriers for improving drug solubility, bioavailability, stability, and therapeutic efficacy is discussed.