Take a bath 90 minutes before bedtime to get better sleep

13 Aug Take a bath 90 minutes before bedtime to get better sleep

A Systematic review, which is a method used to analyse data, was done by a group of Biomedical engineers at the University of Texas in Austin US, in order to check how one warm shower before bed could be linked to a better way for people to improve sleep.

The researchers analysed thousands of studies linking water-based passive body heating (PBHWB) (or bathing and showering with warm/hot water), with improved sleep quality. They checked specifically the sleep onset latency, which is the length of time it takes to accomplish the transition from full wakefulness to sleep; total sleep time; sleep efficiency, that is the amount of time spent asleep relative to the total amount of time spent in bed intended for sleep; and subjective sleep quality.

In regards to the water-based passive body heating they found that a temperature of 40–42.5 °C was associated with both improved self-rated sleep quality and sleep efficiency, and when scheduled 1–2 hours before bedtime, can reduce sleep onset latency by at least 10 minutes.

How is this possible?

Much of the science to support links between water-based body heating and improved sleep is already well-established. For example, it is understood that both sleep and our body’s core temperature are regulated by a circadian clock located within the brain’s hypothalamus that drives the 24-hour patterns of many biological processes, including sleep and wakefulness.

Body temperature, which is involved in the regulation of the sleep/wake cycle, exhibits a circadian cycle, being 2-3 degrees °F higher in the late afternoon/early evening than during sleep, when it is the lowest. The average person’s circadian cycle is characterised by a reduction in core body temperature of about 0.5-1 °F around an hour before usual sleep time, dropping to its lowest level between the middle and later span of night time 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.

The researchers found the optimal timing of bathing to cool down the core body temperature in order to improve sleep quality is about 90 minutes before going to bed. Warm baths and showers stimulate the body’s thermoregulatory system, causing a marked increase in the circulation of blood from the internal core of the body to the peripheral sites of the hands and feet, resulting in efficient removal of body heat and 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 quickly but also of experiencing better quality sleep.



  1. Shahab Haghayegh, Sepideh Khoshnevis, Michael H. Smolensky, Kenneth R. Diller, 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, Volume 46, 2019, Pages 124-135, ISSN 1087-0792, https://doi.org/10.1016/j.smrv.2019.04.008.
  2. University of Texas at Austin. (2019, July 19). Take a bath 90 minutes before bedtime to get better sleep. ScienceDaily. Retrieved August 12, 2019 from sciencedaily.com/releases/2019/07/190719173554.htm