Thermal properties of human skin related to nondestructive measurement of epidermal thickness.

The thermal and physical properties of skin are reviewed briefly in the light of their relationship to skin functions and their influence on temperature measurement and related methodology. Thermal conductivity and epidermal thickness have a direct bearing on the majority of skin functions as these significantly affect heating rates, thermal pain thresholds, and blister formation, as will be seen from the experimental data. The accumulated data on both temperature and pain threshold are used to estimate epidermal thickness in the intact individual. The procedure to accomplish this end utilizes the measured thermal pain threshold, surface temperature, exposure time, and incident energy on a standardized skin site (volar surface of the forearm) to obtain conductivity values. These values are then used in a two-layer system heat flow equation to determine epidermal thickness in other skin sites (fingers) referred to the standard area. Systematic exposures to various materials at high temperatures in contact-burn studies provide data for checking the reliability of this procedure by alternative computations and comparison with predicted tissue temperatures derived from earlier work. Certainly, blister formation and physical measurement of the excised epidermis would provide direct verification of the accuracy of the procedure but these measures have not been undertaken. It is quite possible that over a period of time verification data could be accumulated incidentally in the clinic where skin grafting procedures are carried out. For this purpose only relatively simple measurements of skin temperature and pain threshold, as described herein, would be required to be performed on skin graft donors to provide epidermal thickness measurements for comparison with direct measurements of excised skin immediately after removal.