We modify the Pennes model by taking into account the thermal relaxation time of biological tissue. Specifically, we employ the Maxwell-Cattaneo thermal flux law, in conjunction with the fourth power law, to model the effects of high thermal radiation on such skin. The skin is considered to be a 3D triple-layered structure with embedded dendritic countercurrent multi-level blood vessels, artery and vein, where the dimensions and blood flow of the multi-level blood vessels are determined based on the constructal theory of multi-scale tree-shaped heat exchangers. The method is illustrated by a numerical example. (C) 2008 Elsevier Ltd. All rights reserved.