Biophysical measures of skin tissue water: variations within and among anatomical sites and correlations between measures.

BACKGROUND: Biophysical measures to assess that skin water includes stratum corneum hydration via capacitance (SC), dermal water via tissue dielectric constant (TDC), and transepidermal water loss (TEWL). Since skin differs among anatomical sites and tissue depth we sought to determine the site and depth variability of these measures and their relationships. METHODS: Measurements were done at 17 skin sites from forehead to foot in 32 supine healthy women. Measurements included SC at 1.25 MHz, TDC at 300 MHz to depths of 0.5, 1.5, and 2.5 mm and TEWL. RESULTS: Tissue dielectric constant decreased with increasing depth at forehead, forearm, and calf; increased with depth at palm, thenar eminence and great toe; and was independent of depth at cheek, hand dorsum, thumb pulp, and foot dorsum. SC correlated with TDC at most sites and depths. TEWL correlated with TDC at 2.5 mm only at calf sites and thenar eminence. CONCLUSIONS: Results establish parameter ranges for each measure, show that TDC values do not necessarily change with skin depth, and show a significant correlation between TDC and SC values at most sites. These correlations suggest that SC hydration but not TEWL is directly linked to dermal tissue water levels in normal skin