Water Content of Stratum Corneum in Vivo

Investigations are reported on the nature of the water holding mechanisms in stratum corneum, how certain physical properties of the stratum corneum are altered with changes in water content, and the feasibility of correlating a change in one externally measured physical property with changes in water content. In the first phase of the project the authors have developed methodology which permits the rapid accurate and reproducible assessment of values of heat conduction constants in small samples of material. The results of these experiments show that while there is a three-fold increase in the value of heat conduction constants from the dry to the hydrated state of stratum corneum, the relationship is not predictive in a quantitative sense. Extremely small surface electrodes can be fabricated using microcircuit technology for measuring the sheet resistance of thin layers such as normal thickness stratum corneum. Changes in electrical resistance must be interpreted in light of tissue pathways for ion transport, sweat gland activity, and other generator potentials. (Modified author abstract)