Research Summary:
Objectives: Diethyltoluamide and ethylhexyl p-methoxycinnamate (OMC) are two active ingredients commonly found in insect repellent and sunscreen products, respectively. The concurrent application of these two substances often increases their systemic absorption, compromising the safety and efficiency of cosmetic products. In this study, diethyltoluamide and OMC were incorporated into solid lipid nanoparticles, a colloidal drug delivery system, to reduce percutaneous absorption, avoid toxic effects, and maintain the efficacy of the two active compounds on the skin surface for a long duration.
Methods: Solid lipid nanoparticles were prepared using an ultrasonication technique and characterized by differential scanning calorimetry (DSC) analyses. In-vitro studies were conducted to determine the percutaneous absorption of diethyltoluamide and OMC.
Key findings: DSC data on unloaded and diethyltoluamide- and/or OMC-loaded solid lipid nanoparticles revealed that diethyltoluamide and OMC modified the temperature and the enthalpy change associated with the calorimetric peak of the solid lipid nanoparticles. The concurrent presence of both compounds in the solid lipid nanoparticles caused a synergistic effect, indicating that the lipid matrix of the nanoparticles guaranteed high encapsulation of both diethyltoluamide and OMC. Results from the in-vitro study demonstrated that the nanoparticles were able to reduce the skin permeation of the two cosmetic ingredients compared to an oil-in-water emulsion.
Conclusions: This study has provided supplementary evidence on the potential of lipid nanoparticles as carriers for the topical administration of cosmetic active compounds.
Keywords: diethyltoluamide; differential scanning calorimetry; ethylhexyl p-methoxycinnamate; percutaneous absorption; solid lipid nanoparticles.
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