Competing influences of mental stress and melatonin on skin temperature regulation

Introduction: In preparation for sleep, endogenous melatonin release increases distal skin temperature due to elevated skin blood flow, which contributes to reductions in core body temperature. The distal-to-proximal skin temperature gradient (DPG) is a well-documented physiological predictor of sleep onset. Psychological stress has been shown to disrupt sleep onset, though the underlying mechanisms remain unknown. One potential mechanism may be stress-induced peripheral vasoconstriction and decreased blood flow to the extremities. These effects may attenuate the beneficial influence of melatonin on sleep onset processes (i.e., distal vasodilation and core temperature decline). The aim of this study was to investigate the thermoregulatory response to a psychosocial stress task with and without melatonin supplementation to evaluate if melatonin modifies thermoregulatory stress responses. We hypothesized that stress would have a significant effect on lowering distal skin temperature, and that this response would be blunted with melatonin supplementation. Methods: 10 participants (5 male, 5 female; age: 20 ± 1 years; BMI: 23 ± 4 kg/m 2 ) ingested either a melatonin (3mg) or placebo (sugar) pill in a randomized, repeated-measures, crossover design. Following ingestion, participants rested for 45 minutes, after which they were subjected to an afternoon (~4-5PM) Trier Social Stress Test (TSST) which included resting baseline (5min), nonverbal speech preparation (5min), judged speech (5min), judged mental arithmetic (5min), and recovery (5min) periods. Throughout the task, participants wore a thermoneutral (33°C), water-perfused suit. Distal and proximal skin temperature were recorded, and the DPG was calculated as the difference between subjects’ hands and forearm/shoulder temperature at baseline and throughout the TSST. Participants repeated the same protocol in the opposite condition one month later. Repeated measures ANOVA were used to examine the influence of time (i.e., stress), condition (placebo vs. melatonin), and their interaction on distal skin temperature at proximal (forearm and wrist) and distal (hand) anatomical regions. Results: We observed an effect of stress (p< 0.001), characterized by significant reductions of distal skin temperature from baseline starting at minute 3 of the nonverbal speech preparation phase across both conditions. A significant effect of condition was observed whereby melatonin supplementation elevated skin temperature relative to placebo (p=0.016). Specifically, the DPG was more negative (i.e., colder extremities) throughout the stress task following placebo (-4.1±2.4°C) versus melatonin supplementation (-1.7±1.5°C). Melatonin’s effects were primarily driven by elevated distal skin temperature (Placebo: 29.7±2.1 vs. Melatonin: 31.7±1.5°C, p=0.032), as proximal skin temperature was comparable between conditions (Placebo: 32.3±0.9 vs. Melatonin: 32.4±0.6°C, p=0.740). There were no significant interactions between melatonin and stress on DPG (p=0.860). Conclusion: Distal skin temperature responded similarly to mental stress regardless of melatonin administration. This study suggests that melatonin’s effects on peripheral skin blood flow are unable to fully override the impact that stress has on skin temperature regulation. Stress-induced impairments in thermoregulation may be a candidate physiological mechanism underlying the deleterious influence of acute stress on sleep onset processes. Further studies investigating the combined influence of both melatonin and stress reduction strategies to optimize sleep appear warranted. Funding: Sleep Research Society Foundation (02-SRG-23) This abstract was presented at the American Physiology Summit 2026 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.