Objectives: Radon is a major feature of radioactive springs. According to an official notification article in Japan, bathing in radioactive springs may alleviate the effects of hyperuricemia (gout), rheumatoid arthritis, and ankylosing spondylitis. This study focuses on changes in the body during the use of a low-temperature sauna at a radioactive hot spring.Methods: In this study, we measured the core temperature, skin temperature, and skin blood flow, and performed an emotional assessment (Mood Check List-Short form.2 (MCL-S.2), Visual Analog Scale (VAS), and Numerical Rating Scale (NRS)) in individuals using a sauna at a radioactive spring. Eight healthy adults participated in this study. All participants partook in two sauna interventions, including one sauna with a high radon concentration (approximately 710 Bq/m3) and one with a low radon concentration (approximately 140 Bq/m3). The indoor temperature and relative humidity of the sauna room were approximately 38°C and 78%, respectively. All participants remained in the sauna room for 40 min, and then rested in an antechamber for 40 min.Results and Discussion: Comparing the MCL-S.2 scores, a significant increase was observed in the pleasantness score in the radon intervention. In addition, after comparing the VAS scores, significant improvements in the feelings of coldness and stress were observed only in the radon intervention. Moreover, skin blood flow increased for a longer duration in the radon sauna intervention than the control intervention. The results suggest that using radon saunas gives rise to positive effects, including reducing coldness, feelings of stress, and promoting blood circulation.