A 3-min bath in 47°C hot-spring water called ‘jikan-yu’ has been recommended for over 130 years at Kusatsu-spa. There is a traditional custom of pouring hot-spring water of the same temperature over the head before entering the bath to avert an afflux of blood to the brain. The medical significance of this custom was investigated in 8 healthy male volunteers (age 31±6 years and body mass index 22.4±1.6kg/m²). There were no significant differences in plasma levels of corticotropin-releasing hormone (CRH), adrenocorticotropic hormone (ACTH), cortisol, and β-endorphin on a comparison of findings before and after the action of pouring 20 pails of 47°C hot-spring water over the parietal and occipital areas of the head. However, the direct effect of heat stress on the internal thermosensor in the anterior hypothalamus regulating heat loss and thermogenesis was not examined in this study. Thus, it is considered that the action does not provide a direct hyperthermal stimulus to the brain stem to release stress hormones but may dilate blood vessels of the head to prepare for the abrupt afflux into the cerebral circulation of blood heated by subsequent very hot hot-spring bathing.

We have investigated change in platelets and the blood coagulation and fibrinolytic systems as a mechanism of the onset of thrombotic diseases during and after hot-spring bathing. In this study, We examined effect of 10min 42°C and 37°C hot-spring bathing on protein C, protein S and antithrombin III in seven healthy male subjects. The mean values of protein C antigen, protein C activity, total and fee protein S antigens, protein S activity and antithrombin III activity were slightly increased by both methods, while these changes were not statistically significant. Taken together with our previous reports, 10min 42°C hot-spring bathing gives no effect on the blood coagulation system.