The Effect of Air Humidification on Symptoms and Perception of Indoor Air Quality in Office Workers: A Six-Period Cross-Over Trial

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Abstract
The objective of this study was to evaluate the effect of air humidification on (a) the dryness of the skin and mucosa, (b) allergic and asthmatic reactions, and (c) the perception of indoor air quality. A total of 290 office workers at the Pasila Office Center were included in a six-period cross-over trial. One wing of the building was operated with 30–40% humidification, and the other wing operated under conditions of no air humidification (relative humidity from natural conditions was 20–30%). The length of each study period was 1 work wk. The workers were instructed to keep a structured daily diary of their symptoms, their perception of the indoor air, and potential determinants of the symptoms. A total of 211 (72.6%) workers who returned at least two weekly diaries, and who had experienced both humidified and nonhumidified conditions, were included in the analyses. The primary outcome—dryness symptom score—was characterized by dryness, irritation or itching of the skin and eyes, dryness or irritation of the throat, and nasal dryness. Means of the daily symptom scores and perception ratings during the humidified and nonhumidified periods were calculated for each participant, and intraindividual differences in the means were used to assess the effect of air humidification. The dryness symptom score was significantly smaller during the humidified phase than during the reference phase (paired t test; p < .05). Allergic symptoms that were considered as a separate outcome, a sensation of dryness, and draft were also significantly less frequent during the humidification phase (p < .05). The perception of stuffy air increased during the humidification phase (p < .01). These results suggest that dryness of the skin and mucosa, allergic reactions, and the sensation of dryness can be alleviated by proper air humidification.