A comparative histological study on the skin occlusion performance of a cream made of solid lipid nanoparticles and Vaseline.

The water content of the epidermis is a main factor in maintaining skin smoothness and elasticity and preventing skin dryness. Occlusive products can greatly affect skin hydration by forming a barrier on the skin following the topical administration of oil-based formulations. These products repair the skin barrier by restoring the skin lipids as well. Solid lipid nanoparticles (SLNs) have recently been introduced as a novel carrier with several benefits in pharmaceutics and cosmeceutics. It has been suggested that SLNs may have an occlusive effect following topical application. In this study, the occlusion effects of lipidic particles in different size ranges were investigated in vitro, ex vivo, and in vivo, and the results were compared with the positive (vaseline) and negative (blank) controls. Although larger lipidic particles showed better occlusion properties than nanoparticles in vitro, but ex vivo experiments confirmed the benefits of nanoparticles (almost 30% higher occlusion factor for particles in the range of 170 nm than ones in the range of 600 and 1800 nm). The superiority of SLN formulation to Vaseline as a positive reference was confirmed by the in vivo study. SLN formulation resulted in much thicker stratum corneum than Vaseline. It was indicated that in vitro and ex vivo study methods may not be a good reflective of the in vivo method for determining the occlusive properties of nanoparticulate systems. It was concluded that formulations containing SLNs can be used as efficient skin moisturizer products.