Understanding Microemulsions and Nanoemulsions in Transdermal Delivery

Microemulsions and nanoemulsions are promising vehicles for (trans)dermal drug delivery due to their ability to safely transport clinically relevant drug doses across biological membranes. Their effectiveness is largely attributed to their small dispersion size, which enhances skin permeation. However, the literature lacks clear distinctions between microemulsions and nanoemulsions regarding their definitions, behavior, and specific mechanisms of action. This review aims to deepen the understanding of these vehicles by examining their composition and the role of system constituents in affecting skin structures and drug permeability. It highlights the need for further exploration of mesostructures and the impact of cosolvents, oils, and water on permeation profiles, focusing on formulation systems using ternary diagrams with non-ionic surfactants and other common pharmaceutical components.