We demonstrate that spectral ellipsometry is a suitable optical tool to investigate biological samples such as liver tissue, human nails, and human skin. We have performed ex-vivo as well as in-vivo measurements to obtain via the measured optical parameters Ψ and Δ information's such as layer thicknesses or hydration conditions. As an example for in-vivo studies, a tape stripping study of human skin is shown. Furthermore, we present a hydration study of nails over 48 h following a hydration schedule. The dehydration behavior of the nail is compared with the dehydration behavior of liver tissue. By investigating the change of ñ upon hydration and dehydration, we reveal three different time domains, corresponding to ‘free’ and ‘bound’ water and their respective rate changes.