Essential oil-in-water microemulsions for topical application: structural study, cytotoxic effect and insect repelling activity

Essential oils (EOs) extracted from aromatic plants have been well recognized for their insect repellent properties. Although EOs are effective when freshly applied, their protective effect usually dissipates quickly due to low chemical stability and rapid volatilization of their ingredients. To address this issue, encapsulation in protective carrier materials at the nanoscale is proposed. In this study, oil-in-water (O/W) microemulsions containing geraniol or Citrepel® 75 (citrepel) as the oil phase, a mixture of water and diethylene glycol monoethyl ether (DEGEE) as the aqueous phase and caprylocaproyl polyoxyl-8 glycerides as surfactant were formulated and structurally characterized. DLS analysis showed that the emulsified oil droplets had low polydispersity (PdI