Ambient temperature and humidity are important factors that determine sleep quality. In real-life situations where bedding and clothing are used, sleep is affected more by heat than by cold exposure. Effects of thermal environment on sleep are strongly related to thermoregulation. Increased skin temperature（Tsk） and decreased core body temperature at sleep onset period, and stable Tsk and bed climate during sleep are important for maintaining sleep. Heat exposure increases wakefulness and decreases rapid eye movement sleep（REM） and slow wave sleep（SWS）. In aged subjects, heat exposure increases wakefulness and decreases REM, while no effect is observed on SWS. Furthermore, heat exposure reduces the core body temperature decrease, and increases Tsk, whole body sweat loss, and bed climate humidity both in young and aged subjects. Humid heat exposure further affects sleep stages and thermoregulation. Although the ambient temperature is cold, effects of using electric blankets on sleep and thermoregulation showed similar result to heat exposure, with subjectively dried mouth sensation in the morning. These results indicate that increased thermal stress by humid heat or heated bed climate affects sleep and thermoregulation and might increase dried mouth sensation in the morning.
