Assessment of Personal Relaxation in Indoor-Air Environments: Study in Real Full-Scale Laboratory Houses

The relationship between chemical concentrations in indoor air and the human sense of comfort and relaxation have been reported. We investigated the effect of the sum of volatile organic compounds (sigma VOCs; sum of 79 VOCs) on the level of relaxation in two laboratory houses with almost identical interior and exterior appearances. The electroencephalogram (EEG) was monitored to evaluate the degree of personal relaxation objectively. The experiments were conducted in laboratory houses (LH) A and B with lower and higher levels of sigma VOCs, respectively. A total of 168 healthy volunteers participated, who each performed the task for 20 min, followed by a 10-min break, and EEG was measured during the break. Simultaneously as subjective evaluations, the participants were asked to fill a questionnaire regarding the intensity of odor and preference for the air quality in each LH. The subjective evaluation showed a significant association between sigma VOCs and participants' relaxation (OR: 2.86, 95%CI: 1.24-6.61), and the objective evaluation indicated that the participants were more relaxed in the LH with lower levels of sigma VOCs than that with higher levels (OR: 3.03, 95%CI: 1.23-7.50). Therefore, the reduction of sigma VOCs and odors in indoor air would have an effect, which is the promotion of relaxation.