[ Summary ]
 Human beings of homeothermic animals control their body temperature constantly by regulating thermogenesis and thermolysis against the changes of environmental temperature. However, hyperthermia (heat stroke) occurs easily in sleeping infants, if the mechanism of thermolysis (cooler) is remarkably inhibited by a high-temperature environment or excessive clothing. Adults can take appropriate means against the unpleasant external environment. However, it is impossible for infants to turn over in their sleep, take off their socks, or remove bedclothes by kicking, so we must always care if their environments are pleasant and ensure against risk. During daytime, an infant is often observed by someone. So his/her unusal condition (heat stroke) is possible to detect earlier and SIDS can be avoided. At night, however, the environment surrounding of the infant is dark and his/her parents are often sleeping, so detection of disorder may be delayed and "heat stroke" may result in the worst situation.
 An infant with hyperthermia ("heat stroke") in the cause of external environmental factors has to suppress thermogenesis. Consequently, he/she is obliged to sleep deeply, relax the muscles, and decrease body movement in order to keep his/her body temperature normal. As a homeothermal animal, these behaviors occur commonly. However, if the suppression of thermogenesis lasts for a long time, it may cause serious troubles in the life of the sleepig infant.
To sum up, this new hypothesis suggests that SIDS tends to occur when the following three factors are overlapped each other.
1)External environmental factors (nursing environment) causing hyperthermia (heat stroke)
(1) Excessive clothing, such as caps, gloves, and socks, and bedclothes
(disturbance of thermolysis).
(2) Lying prone in sleeping (disturbance of thermolysis from the
abdomen which release the heat of infants, higher than back).
(3) Long-time sleeping under a high-temperature environment
(in bedclothes, inside warm car, near heater, on hot carpet, in incubator, during bathing, etc.)
2)Characteristics of (SIDS) infants
(1) Infants cannot give a "hazard signal(too hot)" with word.
(2) Infants cannot escape from the unpleasant external environment (high temperature).
3)Human beings are homeothermal animal.
(1) Infants with hyperthermia (heat stroke) keep sleeping more deeply
and relax the muscles to inhibit thier thermogenesis.
(2) Unless the situation with heat stroke is improved, arousal reaction is
retarded. Long-time deep sleeping and relaxation of the muscles cause respiratory inhibition (hypoxemia).
(3) According to the rise of environmental temperature, oxygen
consumption of infants increases.
(4) Release of catecholamines is suppressed during peripheral
vasodilation, especially during sleep.
 The above-mentioned characteristics, 2. and 3. are those of human infants. We adults should pay attention to the item 1. It is the most important for us to understand these characteristics of infants thoroughly, and to give them safe and comfortable environments.
 The new hypothesis described above may not be suitable completely for all the cases of SIDS. In this study, the investigations of central(core) and peripheral deep body temperatures of infants could clarify the thermo-control mechanisms of infants, and the risk of prone-sleeping for SIDS. Nevertheless, it must be necessary to carry out further studies in order to make more clear actual contrivances(=mechanisms) of neuro-regulaion center of temperature and respiration, and other mechanisms of infants. Furthermore, it must be clarified the reasons hastely and scientifically why the bottle-feeding and the smoking, as remained risk factors for SIDS, are dangerous for infants.