Physical and chemical perturbations of the supramolecular organization of the stratum corneum lipids: In vitro to ex vivo study

Background: FTIR spectroscopy is classically used to study the supramolecular organization of the stratum corneum lipids. Exposure to UV_A is responsible for a small decrease in packing observed on cutaneous lipid films. Methods: Lipid films and human skin biopsies were either exposed to UV_A irradiation of 120 J/cm², UV_B irradiation of 0.15 J/cm² or put in contact with ethanol. Using FTIR in vitro and IR microspectroscopy ex vivo provided information on: i) the precise localisation of the stratum corneum in the skin, ii) its thickness, and iii) the organization of its constituted lipids. Results: Different action modes were observed for UV irradiation and the contact with ethanol with a certain destabilisation of the lipidic layer. Ethanol was also found to be responsible for the creation of pores. The destabilisation of the lipid cement was mainly observed ex vivo. Conclusion: The barrier function of the skin is affected by the action of physical and chemical external agents at the molecular level. The increased laxity of the lipid packing could enable the percutaneous penetration velocity of actives.