Submicron emulsions were chosen as a delivery system because they have shown to enhance the penetration of substances into skin due to their particle size and surfactants.26 Submicron emulsions are oil-in-water emulsions with a droplet size below one micrometer. It is a kinetic stable emulsion in which the droplet size is achieved by an incorporation of emulsifiers.27 The oil phase consisted of oleth-3, -10, ethyloleat (Croda, Germany), coco-caprylat/caprat, cetearyl isononanoat (Cognis, Germany) and 0.002% Nile Red, while the aqueous phase consisted of sodium chloride, citric acid, potassium sorbate (Fagron, Germany), magnesium sulfate and glycerol (Caelo, Germany). The surfactant concentration was adjusted to achieve a hydrophilic-lipophilic balance value of 11. All ingredients obtained were of pharmaceutical grade. The physico-chemical properties were recorded to characterize the delivery system. The dynamic light scattering analyzing method (Zetasizer Nano ZS 90, Malvern Instruments, UK) showed a z-average size of with a polydispersity index of . The viscosity of was determined by RheoStress 300 Rheometer (ThermoHaake, Germany). Due to the preservation with potassium sorbate, the pH value was adjusted to .