The water content of the stratum corneum is of utmost importance for the mechanical integrity and the function of this structure. Therefore, many approaches have been used to assess skin hydration, including electrical measurements, infrared spectroscopy, microwave propagation, heat conductivity, photoacoustic spectroscopy and even indirect indicators such as viscoelastic properties, friction, dye fluorescence, and topography.For the use under clinical conditions, non-invasive and relatively unexpensive devices are needed. Several commercially available instruments fulfil these requirements, including the Corneometer, the Nova Meter, the Scicon Hygrometer and a newly developed impedance instrument. However, it has to be kept in mind that these devices do not measure hydration, but electrical indicators of it. Therefore, measurements with different instruments cannot be compared at the current stage. Furthermore, epidemiological data on hydration values in normal and diseased skin are still unavailable. Therefore, single measurements with a given instrument are of no use for the clinician, as long as defined cut-off values to discern between healthy and diseased skin are missing.Routine skin hydration measurements might be useful in the early detection of environmental and occupational skin damage, especially in individuals at increased risk, such as atopics. In addition, these measurements might provide an objective basis for treatment decisions and allow the monitoring of treatment success. In order for hydration measurements to be employed successfully in these clinical situations, defined clinical studies under field conditions are necessary. Only they will show if measurement precision is not inadequately affected by the increased variability of environmental conditions to be anticipated in the clinical setting.