2007, Piran, Slovenia

time(min)
Thermal comfort
WHY DO JAPANESE PREFER TAKING A HOT-WATER BATH?
Hikaru Koshimizu, Youichiro Ichiyanagi, Yutaka Tochihara
Department of Ergonomics, Faculty of Design, Kyusyu University, Fukuoka, 815-8540, Japan
Contact person: koshimiz@design.kyushu-u.ac.jp
INTRODUCTION
Bathing causes physiological and psychological effects in humans such as body temperature
increase, blood pressure decrease and heart rate increase. Since man is naked during bathing,
the effect of the thermal environment is direct. Thus, we postulated that the low ambient
temperature in bathrooms in Japan causes bathing in high-water temperature among Japanese.
To investigate this, we conducted a subjective experiment to measure the influence of the
combination of room ambient temperature and water temperature on human responses.
METHODS
The experiments were conducted in a climatic chamber with a bathtub installed. The ambient
temperature (Ta) conditions were 10, 18 and 26 while the water temperature conditions of
the bath (Tw) were 38, 40 or 42 . Subjects were 8 healthy, Japanese male university
students. Physiological response was assessed by measuring skin temperature, rectal
temperature, blood pressure, heart rate, salivary Ig-A and cortisol. For physiological
responses, thermal sensation vote, thermal comfort vote and acceptability of environment
were asked. Subjects took a bath for 8 minutes, and stayed in the climate chamber for 30
minutes before and after bathing.
Figure 1. Experiment protocol and measurement items
Pretest Room (25 )Climate Chamber (10, 18, 26 ) Bathroom Climate Chamber (10, 18, 26 ) Pretest Room
Body Weight ○ ○
Saliva Collection ○ ○
Heart Rate, Blood Pressure
Skin and Rectal Temperatures
Thermal Sensation and Comfort
-10
0 10 20 30 40 50 60 70
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○ ○ ○ ○ ○ ○
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○ ○ ○
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RESULTS
For the results, the mean skin temperatures while bathing were affected by water temperature,
while after bathing, it was affected by both ambient temperature and water temperature.
Rectal temperatures were higher when water temperatures were higher although the ambient
temperatures were low. Blood pressure and heart rate were affected more by ambient
temperature than water temperature. According to the physiological responses, water
temperature had a greater effect on thermal sensation than ambient temperature. However,
after some time, the effects of water temperature decreased while ambient temperature
increased. There were no significant main effects of Ta and Tw on the change in cortisol
levels, but there was a significant main effect of Ta on the change in Ig-A levels.
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