Adverse environmental health effects of ultra-low relative humidity indoor air.

In Japan, relative humidity (RH) shows the lowest achievement rate among the various general air quality standards for work environment. It has been mainly contributed by airtight design of modern buildings and occurrence of dry outdoor air in winter. Furthermore, an ultra-dry air environment of nearly 0% RH is often required in sophisticated industries. In order to assess the adverse health effects of the ultra-dry air environment, using a self-reported questionnaire, we have undertaken a study of over 200 employees of a high-tech device developing laboratory having a room at 2.5% RH (ultra-dry room). Those who worked in the ultra-dry room were identified and the prevalence of symptoms was compared with the other workers. Analysis was performed by Wilcoxon's test and Fisher's exact test. In the ultra-dry room, all the twelve workers covered their skin with long-sleeve clothes, paper caps, paper masks and latex gloves. They reported skin symptoms more often (p<0.05) than the other workers (N=143). The prevalence of atopic dermatitis was also higher in the exposed workers (p<0.05). The complaints of workers in the ultra-dry environment were similar to preceding reports concerning moderately dry environmental exposures. The current precautions to protect the workers from the adverse effects of ultra-low RH appear to be insufficient, indicating that additional measures such as selection of appropriate clothing to mere skin coverage should be considered.