Wet work is the main cause of occupational contact dermatitis in the cleaning industry. Dermatologists and occupational physicians need to base their primary and secondary prevention for workers in the cleaning industry on the characteristics of wet work exposures. We quantified the burden of wet work in professional office cleaning activities with a continuous standardized observation by trained observers of 41 office cleaners. Duration and frequency of wet work exposure and of different cleaning activities were assessed. Wet work made up 50% of such cleaning work. Within a typical 3-hr shift, a mean frequency of 68 episodes of wet work was observed, which classifies office cleaning as wet work. Skin exposure to irritants was markedly different among cleaners who did the same cleaning activities. Reduction in skin irritation can be achieved by training the workers. Because this group of workers, who have a low level of education, has a high risk of developing irritant hand dermatitis, a special effort on training and instruction should be made. A reduction of exposure can be achieved by: using gloves more often; using gloves for a shorter period of time; using gloves while doing activities that otherwise cause the skin to be in contact with water and cleaning substances and washing hands with water only, reserving soap for when the hands are visibly dirty.