Orthorhombically Packed Cosmetic Oils or Formulations Could Ensure Skin Lipid Barrier Stability—An Ex Vivo Porcine Skin Study

Background: The lipid components of the skin barrier have the strongest structure when arranged in an orthorhombic packing. This structure can be influenced by the external supply of lipophilic ingredients. While the benefits of ceramide supplementation are well-documented, the effects of the cosmetic formulation’s oil-based ingredients have been less explored. Methods: The packing structures of commonly used oil and wax ingredients in cosmetics were analyzed using FT-IR. These components were then combined to formulate a cosmetic composition with an orthorhombic packing structure. The strength of the skin barrier was assessed by measuring transepidermal water loss (TEWL), and the lipid packing of the porcine skin was analyzed using FT-IR. Results: In cosmetic oil ingredients, structurally simple oils such as mineral oil and squalane exhibited orthorhombic lipid packing, while more complex oils like isopropyl myristate (IPM) and isononyl isononanoate (ININ) showed hexagonal packing. Based on these structural characteristics, cosmetic formulations were designed by selectively combining oils, waxes, and emulsifiers to achieve a desired packing structure. Formulations incorporating orthorhombically packed oils successfully resulted in orthorhombic overall structures, whereas those including hexagonally packed oils tended to form hexagonal packing. The orthorhombic oils and formulation effectively maintained the structure and function of the porcine skin lipid barrier without disruption. Conclusions: This study demonstrated that orthorhombic oils and emulsions with orthorhombic packing effectively maintained skin barrier integrity, unlike hexagonal structures.