Nanoemulsions for topical delivery: formulation, applications and recent advances.

Nanoemulsion (NE) is a kinetically stable dispersion comprising oil and water stabilised by an emulsifier, having a droplet size of around 20-200 nm. NE offers versatile formulations for lipophilic and hydrophilic drugs by increasing their solubility and permeability thereby improving their bioavailability. Various high energy and low energy techniques such as the phase pH inversion method, solvent diffusion method, and membrane emulsification method are reported to develop NE. The selection of method is crucial, thus a comparison of different methods in terms of droplet size and stability has been provided. This review emphasises the topical application of NE for various skin ailments like psoriasis, skin infection, cancer, wound healing, and many others. This review highlights the advancement in the NE formulation using ionic liquids and nanoparticles, as well as stimuli-responsive and pickering NE. The approaches to overcome the toxicity concern of NE and its constituents specifically surfactant has been discussed.