The effect of repetitive mild hyperthermia on body temperature, the autonomic nervous system, and innate and adaptive immunity was investigated using a new hyperthermia treatment system, nanomist sauna (NMS). Six healthy volunteers participated and the concentration of catecholamines and cortisol, and the frequency and function of leukocytes in the peripheral blood were investigated before and after successive 7 days of hyperthermia treatment (20 min/day, 40°C, 100% relative humidity). After treatment, the blood level of adrenaline and cortisol on the 7th day was decreased compared with the 1st day, indicating the suppression of the sympathetic nervous system activity. Moreover, the frequency of CD56 + NK, CD56 + NKT and B cells on the 7th day tended to be increased compared with the 1st day. The frequency of HLA-DR-positive NK and NKT cells and expression of HLA-DR on B and T cells increased. The cytotoxicity of NK cells and proliferative response of B cells were also elevated. The results indicate that repetitive mild hyperthermia treatment might suppress excessive sympathetic dominance and modify immunity. Additionally, because it can provide the same effects as conventional hyperthermia treatments with minimal burden to the body, NMS may be a novel patient-and elderly-friendly hyperthermia treatment for health promotion.Many researchers have reported that hot springs, saunas and home baths give comfortable and appropriate hyperthermic stimulation. We have also reported a series of studies where systematic mild hyperthermia treatments could activate leukocyte, enhance immunity and treat various diseases (19,28). Thus conventional hyperthermia treatments might be effective for health promotion, including reports that hot-spring treatment is effective for the improvement of locomotive syndromes (14). However, Pilch et al. reported that wet hyperthermia is more stressful than dry hyperthermia for healthy males (22). Furthermore, it is not easy for frail people (especially children, older people and patients with locomotive disorders) to regularly take conventional hyperthermic treatments. For example, the water pressure of baths and the high temperatures (80-100°C) of dry saunas are sometimes stressful and dangerous to these individuals. In addition, conventional wet sauna has the problem of high humidity. Thus aspects of conventional hyperthermia treatments, such as high temperature, water pressure and humidity might induce stress. If such stresses could be lowered, hyperthermia treatment could be useful not only for patients and older people but also for caretakers. To pursue the further study of the effect of hyperthermia itself, we used nanomist sauna (NMS), a
