Characterization of the physical properties of the stratum corneum by a new tactile sensor

BACKGROUND/AIMS: The physical properties of the stratum corneum (SC) change with its water content, which is regulated by the presence of water solutes (natural moisturizing factors) and lipids in the SC, and are considered to be responsible for the induction of desquamation, skin surface roughness, and fine wrinkles. Recently a new type of tactile sensor developed for evaluating the physical properties of objects has been introduced as a simple, non-invasive method to evaluate them; because the data obtained with this sensor have not yet been characterized in detail, we compared them with other physical parameters of the skin. METHODS: A change in resonant frequency (Deltaf ) was measured under various levels of pressure applied by a tactile sensor placed on the cheeks of 29 women. We also measured high-frequency conductance that reflects the hydration state of the skin surface, water holding capacity of the SC, transepidermal water loss (TEWL), skin flexibility, skin elasticity, amino acid composition of the SC, and desquamation index of the SC at the same time, and evaluated the correlation between Deltaf and other physical parameters. RESULTS: The correlation between Deltaf and high-frequency conductance of the SC, and that between Deltaf and the water holding capacity of the SC were substantially high. Deltaf under high pressure was more closely correlated with the acidic amino acid ratio of the SC. Deltaf also showed a correlation with desquamation index for thickness of the SC as well as with skin elasticity, independent of the applied pressure. CONCLUSIONS: Because Deltaf determined with the tactile sensor correlated with other physical parameters specific to the properties of the SC, such as high frequency conductance of the SC, its water holding capacity, ratio of acidic amino acids, and the desquamation index for thickness, the physical properties of the SC may be adequately evaluated with the measurements of Deltaf.