In the UK, approximately 30% of cases of dermatitis reported to the national surveillance scheme are associated with wet working or exposure to aqueous mixtures. There is evidence that the duration and frequency that hands are wet are key determinants of risk, but there are no objective methods to measure these exposure factors. This research aimed to develop a practical tool to measure the duration and the number of occasions hands are wet. We developed an electronic sensor that is worn on the finger, which detects wetness from evaporative cooling. The output signal is recorded in electronic memory and the frequency and duration of exposure calculated using a simple data processing algorithm. The device has been tested in a variety of environmental conditions and for a standardized wet-work task. Wetting events were detectable in all the standardized tests, with the proportion of time the hands were wet ranging from 15 to 49% (mean 30%). The electronic sensor is slightly affected by abrupt changes in air temperature and rapid air movements, but these do not seem to impose any practical limitations. This IOM Wet-Work sampler has the potential to provide reliable measurements of exposure that may be used to assess the risk of contact dermatitis.