Cooling Core Temperature with Warm Bath at Bedtime May Improve Sleep Interview with:

Shahab Haghayegh, Ph.D. Candidate Department of Biomedical Engineering Cockrell School of Engineering University of Texas at Austin

Shahab Haghayegh

Shahab Haghayegh, Ph.D. Candidate
Department of Biomedical Engineering
Cockrell School of Engineering
University of Texas at Austin What is the background for this study? What are the main findings?

Response: I’m a sleep researcher and I wanted to find the link between warm bath and sleep. Body temperature which is involved in the regulation of the sleep/wake cycle, exhibits an endogenous circadian cycle, that is a 24-hour pattern, being highest by 2-3°F in the late afternoon/early evening than during sleep when it’s lowest. The average person’s circadian cycle is characterized by a reduction in core body temperature by ~ 0.5 to 1° F the hour or so before one’s usual sleep time, dropping to its lowest level between the middle and later span of nighttime sleep. It then begins to rise, acting as a kind of a biological alarm clock wake-up signal. The temperature cycle leads the sleep cycle and is an essential factor in achieving rapid sleep onset and high efficiency sleep. What should readers take away from your report?

Response: An easy way to improve your sleep is to take a hot bath or shower 1-2 hours before bed. That’s the optimal timing of bathing for cooling down of core body temperature in order to improve sleep quality and help with falling asleep faster. Warm baths and showers stimulate the body’s thermoregulatory system, causing marked increase in the circulation of blood from the internal core of the body to the outer skin sites of the hands and feet resulting in very efficient removal of heat from the body which causes decline in body temperature. Therefore, if baths are taken at the right biological time– 1-2 hours before bedtime, they will aid the natural circadian process and increase one’s chances of not only falling asleep more quickly but and getting better sleep. What recommendations do you have for future research as a result of this work?

Response: I would recommend more research to find the optimal duration of bath/shower. Also, researches can study the difference in effect of bath and shower, to see if one of them works better. Is there anything else you would like to add? 

Response: I would like to emphasize the importance of timing of the bath/ shower into your nightly routine. Since the body temperature starts to naturally decline as part of its natural circadian cycle about 1-2 hours before the usual bed time. When we take the warm bath or shower in this period, it helps the natural biological circadian process. However, if we take it too close to bedtime, it is too late to be effect and may even disrupt the natural circadian process controlling sleep.


Haghayegh, Shahab, Sepideh Khoshnevis, Michael H. Smolensky, Kenneth R. Diller, and Richard J. Castriotta. “Before-bedtime passive body heating by warm shower or bath to improve sleep: A systematic review and meta-analysis.” Sleep medicine reviews (2019). 

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Last Updated on August 7, 2019 by Marie Benz MD FAAD