We demonstrate the application of terahertz pulse imaging for the in-vivo study of human tissue, in this case the upper layers of human skin. The terahertz pulses comprise frequencies from below 100 GHz to over 2 THz and are generated using optical pulse excited semiconductor devices with a conversion efficiency of better than 10-3. The terahertz pulses are used to obtain tomographic information on the skin surface tissue. From the data the stratum corneum thickness and hydration may be mapped or cross-sectional images displayed.