Inter- and intra-individual differences in human stratum corneum lipid content related to physical parameters of skin barrier function in vivo

For a full understanding of the properties of the human skin barrier, physi cal macroscopic parameters of barrier function must be correlated to the st ructural organization of the barrier on a molecular level. This study was u ndertaken to relate differences in the relative composition of the three ma in lipid classes of human stratum corneum, i.e., free fatty acids, choleste rol, and ceramides, to differences in transepidermal water loss, stratum co rneum electrical impedance, and corneometer value. A new high performance l iquid chromoatography/light scattering detection-based analysis method rece ntly developed was used for collection of quantitative lipid data in conjun ction with gas chromatography/mass spectrometry/flame ionization detection measurements on the free fatty acid fraction. After subtraction of contamin ating lipid fractions we have estimated the molar ratio of the human skin b arrier lipid composition to be, respectively, 15% cholesterol esters, 16% s aturated long chain free fatty acids, 32% cholesterol, and 37% ceramides, T he inter-individual difference in the relative amount of free fatty acids, cholesterol, and ceramides, respectively, can be >100% in the individual ca se. It was found that the relative amount of ceramides to cholesterol is la rger in the wrist area, paralleled by a higher transepidermal water loss an d corneometer value as well as different skin electrical impedance values a s compared with the upper forearm area. We conclude that the site-dependent differences in the stratum corneum lipid composition are small compared wi th the large inter-individual variation. Interestingly, in the individual c ase, no correlation was registered between relative ceramide content and ba rrier properties.