Efficient transdermal delivery of hydrophobic small-molecule drugs remains a persistent challenge in dermatological 

therapeutics due to the limited solubility of active materials, stability of formulation, and the physical barrier posed by 

the stratum corneum. Here, we report a one-step emulsification strategy that enables the formation of water-in-oil-in-water 

(W/O/W) double emulsions and water-in-oil (W/O) single emulsions using silica nanoparticles as the sole stabilizer. A 

hydrophobic usnic acid derivative active material, usnic acid-cinnamic acid (UA-CA), was solubilized in aqueous solvents

by the precise control of the polarity by addition of organic solvents. The aqueous phase was then incorporated into 

emulsions through a vortexing step with oil phase without the use of surfactants or multi-step emulsification processes. 

By tuning the polarity and volume fraction, phase behavior was correlated with emulsion morphology, demonstrating 

phase-inversion-driven enclosure of the inner dispersed phase to form double emulsions. While stable double emulsions 

and single emulsions with high UA-CA concentrations were successfully fabricated, ex vivo porcine skin permeation 

experiments revealed negligible transdermal transport efficacy (Cpermeate/Cfeed<10–5) of the drug. These results highlights 

trade-off relationship between the emulsion stability and skin permeability, providing design principles for next-generation 

topical formulations.