Research
Mixed
Heat exposure during sleep increases wakefulness and decreases slow wave sleep (SWS) and REM sleep, primarily by suppressing the normal nocturnal decline in core body temperature (Tcore) and increasing skin blood flow.
To optimize sleep, keep your bedroom cool enough to allow your core body temperature to drop. Heat exposure, especially humid heat, disrupts deep sleep (SWS) and REM by preventing this natural cooling process. Use air conditioning or cooling bedding to maintain a thermoneutral environment, particularly during the first half of the night.
GoodSupportsHIGH confidence
Heat load suppresses the decrease in Tcore and increases Tsk and whole body sweat loss during sleep... This suppressed decrease in Tcore may disturb sleep at the initial segment of sleep.
Why this rating
Based on multiple human studies cited, including semi-nude and real-life conditions.
Source
Effects of thermal environment on sleep and circadian rhythm
Kazue Okamoto-Mizuno et al. · Journal of PHYSIOLOGICAL ANTHROPOLOGY · 2012
DOI 10.1186/1880-6805-31-14
narrative_reviewCited 450×
Read the paper DOI resolved against Crossref · corpus check 2026-06-10
More from this paper
- Cold exposure during sleep does not significantly disrupt sleep stages (SWS/REM) when bedding and clothing are used, but it significantly alters cardiac autonomic activity (increasing parasympathetic dominance) without affecting subjective sleep quality.Good
- Humid heat exposure has a more severe disruptive effect on sleep stages (specifically SWS) than dry heat, particularly when exposure occurs in the initial segment of sleep.Good
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