What causes sweating during Rapid Eye Movement (REM) sleep?

Causes of Sweating During REM Sleep

Sweating during REM sleep occurs primarily due to reduced thermoregulatory efficiency and altered autonomic control, with the sweat response being significantly diminished compared to other sleep stages due to decreased sensitivity of the thermoregulatory system during REM. 1

Physiological Mechanisms in REM Sleep

Thermoregulatory Changes

• For a given core body temperature, sweating is lowest during REM sleep compared to all other sleep stages, with the mechanism involving a reduced slope of the sweat rate-to-core temperature relationship rather than a change in the temperature threshold for sweating onset 1
• The thermoregulatory system shows decreased excitability and sensitivity specifically during REM sleep, making sweating responses less robust even when body temperature rises 1

Autonomic Dysregulation

• During REM sleep, muscle tone reaches its nadir and upper airway muscles (except nasal and laryngeal dilators) become atonic, which can contribute to autonomic instability 2
• Loss of rib cage stabilization occurs due to inspiratory intercostal muscle inhibition during REM sleep, potentially affecting respiratory-related autonomic functions 2, 3

Pathological Causes of REM Sleep Sweating

Sleep-Disordered Breathing

• Obstructive sleep apnea is strongly associated with nocturnal sweating, with 30.6% of male and 33.3% of female OSA patients reporting frequent sweating (≥3 times per week) compared to only 9.3% of men and 12.4% of women in the general population 4
• Sympathetic overactivity from repetitive apneic events drives excessive sweating, though objective polysomnography findings (apnea-hypopnea index) do not always correlate with subjective sweating complaints 5, 6
• Successful PAP therapy dramatically reduces frequent nocturnal sweating from 33.2% to 11.5%, confirming OSA as a reversible cause 4

Circadian and Inflammatory Factors

• Cortisol nadir, increased skin temperature, and poor barrier function during nighttime hours can promote sweating, particularly in inflammatory conditions 2
• Circadian dysregulation with shifted cortisol rhythms and increased melatonin levels may result in increased systemic inflammation that triggers sweating 2

Medication Effects

• Serotonergic antidepressants can induce or exacerbate REM sleep abnormalities and potentially affect autonomic functions including sweating 3

Clinical Approach

Key Diagnostic Considerations

• Screen for obstructive sleep apnea in any patient complaining of nocturnal sweating, as this is the most common and treatable cause 4
• Evaluate for associated symptoms: daytime fatigue, snoring, breathing trouble at night, morning headaches, and restless legs symptoms, all of which correlate with night sweats 6
• The American Academy of Sleep Medicine recommends polysomnography when abnormal sweating during sleep is reported to differentiate between various sleep disorders 3

Treatment Considerations

• For primary sleep hyperhidrosis unrelated to other sleep disorders, oxybutynin (a muscarinic receptor-blocking anticholinergic) can provide excellent efficacy with minimal side effects 7
• Address underlying sleep disorders first, as treating OSA with PAP therapy normalizes sweating prevalence to general population levels 4

Important Caveats

• Subjective reports of night sweats often do not correlate with objective polysomnography findings (sleep onset latency, arousal index, periodic leg movements), making clinical history alone insufficient for diagnosis 6
• The mechanism of sweating may differ between thermoregulatory and emotional/psychological sweating, with some cases showing characteristics of the latter (ammoniacal odor, sensation of coldness) 7
• Younger age, cardiovascular disease, hypertension, and insomnia symptoms are all associated with increased nocturnal sweating independent of sleep stage 4