Thermal stress and the body
Heat and the brain
Cognitive and psychological benefits
Risks and limitations
Clinical research and emerging studies
Heat that heals?
Long before modern medicine, cultures turned to heat as a therapeutic force. The ritual of exposing the body to intense heat — whether in Finnish saunas, Turkish hammams, or Japanese onsens — has served as a method of renewal, resilience, and recovery.
Thermal therapies, such as sauna use and hot yoga, have recently surged in popularity across wellness and medical communities. Rooted in ancient traditions, such as the Finnish sauna, these heat-based practices are now being reevaluated through the lens of modern medicine.
With an increasing body of peer-reviewed literature substantiating their biological effects, heat exposure has garnered interest for its potential to positively influence cardiovascular function, brain health, metabolic regulation, and psychological well-being.1–4
This article examines the current scientific understanding of how controlled thermal stress influences human physiology and neurology.
Image Credit: DRistimaki/Shutterstock.com
Thermal stress and the body
Exposure of the body to heat triggers a complex cascade of physiological responses aimed at maintaining homeostasis. When the body encounters elevated temperatures, thermoregulatory systems initiate physiological processes such as vasodilation, increased cardiac output, and stimulation of sweat production to dissipate heat.1
The acute cardiovascular response to heat stress includes elevated heart rate and reduced systemic vascular resistance, which mirrors the effects of moderate aerobic exercise.
Regular sauna bathing has been shown to improve endothelial function and arterial flexibility, particularly in individuals with cardiovascular risk factors.2 The mechanism involves enhanced nitric oxide bioavailability and reduced arterial stiffness, contributing to improved vascular health over time.3
Heat exposure also mobilizes immune responses. Elevations in circulating leukocytes and cytokines such as interleukin-6 (IL-6) have been observed following sauna or hot water immersion, indicative of transient immune activation.3
Additionally, repeated exposures may build thermotolerance, and promote resilience against physiological stressors. Furthermore, while the mechanisms are still being studied, there is evidence that heat therapy may modulate systemic inflammation and reduce oxidative stress, both of which are critical factors in chronic diseases.1
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Heat and the brain
Thermal therapy exerts direct and indirect effects on the central nervous system. One of the key mechanisms is the induction of heat shock proteins (HSPs), which act as molecular chaperones to preserve protein integrity and support mitochondrial function.4
These proteins have been implicated in neuroprotection and the mitigation of pathological protein aggregation seen in neurodegenerative diseases such as Alzheimer’s disease.
Moreover, heat exposure is also known to influence neurochemical pathways. Elevated core body temperature is associated with increased release of endorphins, dopamine, and brain-derived neurotrophic factor (BDNF), which are crucial for mood regulation, synaptic plasticity, and cognitive function.2,4
Additionally, exposure to passive heat stress has been linked to the upregulation of BDNF in the hippocampus, a brain region essential for memory formation.5
The modulation of neurotransmitters and increased blood flow to the brain has been shown to enhance mental clarity, sleep quality, and mood.2 Furthermore, regular heat therapy sessions have also been associated with the alleviation of depression and anxiety symptoms and a sense of relaxation and well-being.3
These findings suggest that thermal therapies may facilitate neuroplasticity and cognitive maintenance, particularly in populations at risk of cognitive decline. Emerging evidence supports this potential, with heat exposure linked to improved memory performance and executive function in older adults.6
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Cognitive and psychological benefits
Controlled human studies increasingly substantiate the psychological benefits of thermal exposure. Hot yoga, which combines the benefits of traditional yoga practice with ambient heat (typically ~40.5 °C), has been associated with reduced perceived stress, enhanced mood, and lower depressive symptoms.7
The combined effect of physical exertion, mindfulness, and heat may account for the unique mental health benefits of this practice.8
Regular sauna use has also been inversely associated with the risk of developing psychotic disorders and dementia.2 These correlations are hypothesized to result from the cumulative effects of heat on vascular function, neuroinflammation, and stress hormone regulation.
Additionally, cortisol, the body’s primary stress hormone, has been observed to decrease following repeated thermal exposure, suggesting a normalization of the hypothalamic-pituitary-adrenal (HPA) axis response.7
Researchers believe that this hormonal adjustment may be the underlying cause of the calmness and mental clarity experienced after sauna or hot yoga sessions.
Heat therapy can also complement and augment the benefits of physical exercise. Studies have shown that combining heat therapy with exercise can improve cardiovascular fitness and exercise tolerance.1,3
For instance, sauna yoga, which combines yoga practice with heat exposure, has been found to enhance flexibility, strength, and balance in older adults.9
Risks and limitations
Despite the array of benefits, heat-based therapies carry potential risks. Acute heat stress can cause dehydration, electrolyte imbalance, and heat exhaustion, particularly in vulnerable populations such as the elderly, pregnant women, or individuals with cardiovascular compromise.3
Individuals with certain cardiovascular conditions, such as recent myocardial infarction, severe aortic stenosis, or uncontrolled hypertension, should be especially cautious while opting for heat therapies. The increase in heart rate and blood flow can pose risks for these individuals.2
Furthermore, thermoregulatory capacity is known to diminish with age and certain medical conditions. Impaired sweating, reduced cardiac reserve, or autonomic dysfunction may increase the likelihood of adverse events. Therefore, individual risk assessment and appropriate acclimatization are essential when initiating thermal therapy protocols.6
Additionally, the duration and intensity must be carefully managed. Excessive heat exposure can be counter-productive by inducing oxidative stress and neuroinflammation or exacerbating pre-existing medical conditions.
As with any therapy, practitioners strongly recommend personalization and clinical supervision.
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Clinical research and emerging studies
Recent clinical investigations have advanced the understanding of how repeated passive heat exposure contributes to systemic health benefits. In a randomized controlled trial, hot water immersion conducted three times per week over eight weeks improved fasting glucose levels reduced arterial stiffness, and enhanced mood in sedentary adults.1
These findings align with mechanistic data suggesting that heat acts as a metabolic modulator through pathways involving insulin sensitivity and mitochondrial biogenesis.
Notably, passive heat exposure appears to mimic some effects of physical exercise, making it a potential adjunct or alternative for individuals unable to engage in regular physical activity due to mobility limitations or chronic illness.
In neurological research, heat therapy has gained traction for its putative role in delaying or preventing the progression of Alzheimer’s disease.
One study from 2020 discusses how the activation of heat shock proteins improves cellular proteostasis (the regulation of the proteome), reduces neuroinflammation, and enhances mitochondrial dynamics, which are all hallmarks of neurodegenerative pathology.4
Another study demonstrated that heat exposure increased hippocampal volume and functional connectivity in key brain networks associated with attention and memory.
These structural adaptations and changes also support the hypothesis that heat may serve as a non-pharmacological intervention to preserve cognitive function.6
Heat that heals?
In summary, heat exposure through sauna therapy and hot yoga presents a compelling, evidence-based approach to enhancing physiological and neurological health.
The cardiovascular benefits, including improved endothelial function and reduced systemic inflammation, align with improved metabolic outcomes such as insulin sensitivity and lipid regulation.
At the same time, the upregulation of heat shock proteins and neurotrophic factors supports the claims of enhanced brain function and psychological well-being associated with thermal therapy.
Nevertheless, the application of thermal therapies must be approached with clinical prudence, particularly for at-risk populations.
Furthermore, continued investigation, particularly through randomized trials in diverse cohorts, is required to refine protocols, validate outcomes, and explore the long-term safety of thermal therapy.
In the evolving landscape of integrative medicine, sauna therapy and hot yoga may emerge as accessible and non-invasive strategies for promoting systemic resilience and cognitive longevity.
Their potential role in the prevention and management of chronic diseases also emphasizes the need for further interdisciplinary research and clinical translation.
References
- Brunt, V. E., & Minson, C. T. (2021). Heat therapy: mechanistic underpinnings and applications to cardiovascular health. Journal of Applied Physiology, 130(6), 1684–1704. DOI:10.1152/japplphysiol.00141.2020
- Laukkanen, J. A., & Kunutsor, S. K. (2024). The multifaceted benefits of passive heat therapies for extending the healthspan: A comprehensive review with a focus on Finnish sauna. Temperature, 11(1), 27–51. DOI:10.1080/23328940.2023.2300623
- Hussain, J., & Cohen, M. (2018). Clinical Effects of Regular Dry Sauna Bathing: A Systematic Review. Evidence-Based Complementary and Alternative Medicine, 2018, 1857413. DOI:10.1155/2018/1857413
- Von Schulze, A. T., Deng, F., Morris, J. K., & Geiger, P. C. (2020). Heat therapy: possible benefits for cognitive function and the aging brain. Journal of Applied Physiology, 129(6), 1468–1476. DOI:10.1152/japplphysiol.00168.2020
- Kojima, D., Nakamura, T., Banno, M., Umemoto, Y., Kinoshita, T., Ishida, Y., & Tajima, F. (2018). Head-out immersion in hot water increases serum BDNF in healthy males. International Journal of Hyperthermia, 34(6), 834–839. DOI:10.1080/02656736.2017.1394502
- Cheng, J. L., & MacDonald, M. J. (2019). Effect of heat stress on vascular outcomes in humans. Journal of Applied Physiology, 126(3), 771–781. DOI:10.1152/japplphysiol.00682.2018
- Henderson, K. N., Killen, L. G., O'Neal, E. K., & Waldman, H. S. (2021). The Cardiometabolic Health Benefits of Sauna Exposure in Individuals with High-Stress Occupations. A Mechanistic Review. International Journal of Environmental Research and Public Health, 18(3), 1105. DOI:10.3390/ijerph18031105
- Hunter, S. D., Dhindsa, M. S., Cunningham, E., Tarumi, T., Alkatan, M., Nualnim, N., & Tanaka, H. (2016). Impact of Hot Yoga on Arterial Stiffness and Quality of Life in Normal and Overweight/Obese Adults. Journal of Physical Activity & Health, 13(12), 1360–1363. DOI:10.1123/jpah.2016-0170
- Bucht, H., & Donath, L. (2019). Sauna Yoga Superiorly Improves Flexibility, Strength, and Balance: A Two-Armed Randomized Controlled Trial in Healthy Older Adults. International Journal of Environmental Research and Public Health, 16(19), 3721. DOI:10.3390/ijerph16193721