Sauna
How it works

The cardiovascular response and why it matters

When you enter the sauna, your body faces a thermal challenge it cannot ignore. Core temperature begins to rise. The hypothalamus detects this and initiates a cascade of thermoregulatory responses. Blood vessels in the skin dilate, heart rate increases, cardiac output rises. A 2025 review in Frontiers in Cardiovascular Medicine confirmed that the physiological responses to sauna bathing closely resemble those of moderate to vigorous aerobic exercise. The cardiovascular system works at comparable intensity without the mechanical load on joints and muscles (Sastriques-Dunlop et al., 2025).

The haemodynamic effects are well characterised. Crandall and Wilson (2015) reviewed the human cardiovascular response to passive heat stress comprehensively in Comprehensive Physiology, documenting the mechanisms behind vasodilation, increased cardiac output and the redistribution of blood flow during heat exposure. Skin blood flow increases dramatically as the body attempts to dissipate heat. Blood pressure changes are complex. Acute sauna use causes initial rises followed by significant reductions post-session, and regular use is associated with meaningful reductions in resting blood pressure over time.

For people who cannot exercise intensively due to injury, illness or age, this cardiovascular stimulus is not a minor benefit. It is a rare opportunity to stress the cardiovascular system adaptively, driving the same vascular adaptations that exercise produces, without the physical demand that exercise requires.

Heat shock proteins and cellular resilience

Every cell in your body contains proteins that fold into precise three-dimensional shapes to perform their function. Heat, mechanical stress and chemical insults can cause proteins to misfold, aggregate and accumulate, a process linked to ageing, neurodegeneration and cellular dysfunction. Heat shock proteins are the cell's response to this threat.

When core temperature rises during sauna, cells throughout the body upregulate heat shock protein expression. These molecular chaperones do two things: they help misfolded proteins refold correctly, and they protect other proteins from subsequent stress. Calderwood, Theriault and Gong (2005) documented the relationship between heat shock proteins and immune function specifically, showing that heat-induced HSP expression enhances immune surveillance and the body's capacity to respond to cellular damage.

Ullah et al. (2021) found that heat shock protein 20 promotes sirtuin 1-dependent cell proliferation. Sirtuins are a class of proteins that regulate cellular ageing, inflammation and metabolic function. Grabowska, Sikora and Bielak-Zmijewska (2017) reviewed sirtuins as a promising target in slowing the ageing process in Biogerontology, and the connection between sauna-induced heat shock protein expression and sirtuin activation is one of the most interesting mechanistic pathways in the longevity literature. The heat is not just uncomfortable. It is sending cellular repair signals throughout the body.

Hormesis and the principle of adaptive stress

Hormesis is one of the most important concepts in biology that most people have never heard of. It describes the phenomenon whereby a low-dose stressor that would be harmful at high doses produces beneficial adaptive effects at controlled doses. Exercise is hormesis. Cold exposure is hormesis. And sauna is hormesis.

Calabrese and Mattson (2017) reviewed how hormesis impacts biology, toxicology and medicine in npj Aging and Mechanisms of Disease, describing the fundamental principle that brief, controlled thermal stress activates adaptive pathways that strengthen the body's capacity to handle future stressors. Calabrese, Scuto and Calabrese (2020) extended this specifically to mental health and resilience in Healthy Aging and Longevity, finding that hormetic interventions including heat exposure enhance psychological resilience alongside their physiological effects.

This is the framework that explains why regular sauna use produces cumulative benefits. The body is not just surviving the heat. It is adapting to it, and those adaptations accumulate. Each session builds on the last. The heat acclimatisation that occurs with regular use means the same thermal stress produces a progressively more efficient adaptive response over time.

Nitric oxide, endothelial function and vascular health

One of the primary mechanisms through which sauna produces its cardiovascular benefits is through endothelial nitric oxide synthase. The endothelium is the single-cell lining of every blood vessel in the body, and its health determines whether those vessels can dilate appropriately, resist atherosclerosis and regulate blood pressure effectively.

Heat stress upregulates endothelial nitric oxide synthase, the enzyme that produces nitric oxide in blood vessel walls. Nitric oxide causes blood vessels to relax and dilate, reducing vascular resistance and blood pressure. Kellogg, Zhao and Wu (2009) characterised the roles of nitric oxide synthase isoforms in cutaneous vasodilation during whole body heat stress in the Journal of Applied Physiology, and Sarmah et al. (2022) reviewed the interactions between endothelial nitric oxide synthase, cardiovascular function and pain signalling in Molecules, confirming the multi-system significance of this pathway.

The repeated stimulation of endothelial nitric oxide synthase through regular sauna use trains the vasculature to maintain better baseline function. This is the mechanistic pathway through which the Finnish cohort data translates from epidemiology into biology. The consistent cardiovascular benefit seen over 20-year follow-up periods is the result of repeated endothelial conditioning, session by session.

Brain health, dementia and cognitive protection

The dementia data is the finding that surprises most people. In the Kuopio Ischemic Heart Disease Risk Factor Study, a cohort of 2,315 Finnish men followed for over 20 years, those who used a sauna 4 to 7 times per week had a 66% lower risk of dementia and a 65% lower risk of Alzheimer's disease compared to those who used it once a week. This association held after controlling for age, alcohol consumption, body mass index, blood pressure, cholesterol and smoking (Laukkanen et al., 2017).

The mechanistic explanation involves multiple pathways. Improved cerebral blood flow through nitric oxide-driven vasodilation enhances oxygen and nutrient delivery to brain tissue. Reduced arterial stiffness, documented by Zeki Al Hazzouri and Yaffe (2014) as a key correlate of cognitive decline, is a direct result of regular sauna use. Reduced systemic inflammation removes a known driver of neurodegeneration. And heat shock proteins activated during sauna may directly reduce tau phosphorylation, the process through which tau protein aggregates into the neurofibrillary tangles characteristic of Alzheimer's disease.

The sauna temperatures associated with the greatest dementia risk reduction in the Finnish data were 80 to 99 degrees Celsius, which sits precisely within the range of our traditional steam sauna. This is not coincidental. It is the temperature range at which the cardiovascular and heat shock protein response is most robustly activated.

Sweating, skin health and what sweat actually contains

Sweat is the body's primary heat dissipation mechanism. During a sauna session, sweat rate increases dramatically as the thermoregulatory system attempts to cool the body through evaporation. Baker (2019) reviewed the physiology of sweat gland function comprehensively in Temperature, documenting the composition of sweat and its roles in human health beyond temperature regulation.

Sweat contains water, electrolytes, urea, ammonia and small quantities of various metabolic compounds. Sears, Kerr and Bray (2012) conducted a systematic review of arsenic, cadmium, lead and mercury in sweat in the Journal of Environmental and Public Health, finding evidence that sweat does contain measurable quantities of these heavy metals, though the kidneys and liver remain the primary detoxification organs and the clinical significance of sweat-based elimination is still debated in the literature. The most well-supported skin benefits of sauna relate to the mechanical effects of profuse sweating on pore clearance, skin hydration and sebum regulation rather than systemic detoxification.

The humid heat of steam sauna specifically opens airways and supports mucociliary clearance, the respiratory tract's mechanism for clearing mucus and pathogens. Regular sauna use has been associated in multiple studies with reduced frequency of respiratory infections and improved respiratory function, an effect that is more pronounced with traditional steam than with infrared.

Infrared versus steam: what the research actually shows

The comparison between infrared and traditional steam sauna is one of the most frequently asked questions and one of the most frequently oversimplified. The honest answer is that they produce overlapping but distinct effects, and the right choice depends on what you are using the sauna for.

A 2025 study in the American Journal of Physiology directly compared thermoregulatory, cardiovascular and immune responses to traditional sauna and far infrared sauna and found that traditional sauna produces a greater core temperature rise, stronger cardiovascular response and more pronounced immune activation (Akerman et al., 2025). The Finnish cohort mortality and dementia data is based on traditional steam sauna, not infrared. If cardiovascular conditioning and the evidence-backed longevity outcomes are your primary goal, steam is where the data sits.

For infrared specifically, Mero et al. (2015) confirmed in a peer-reviewed study that far infrared heat penetrates approximately 3 to 4 centimetres into fat tissue and the neuromuscular system, producing deep tissue heating at more tolerable ambient temperatures. Hussain et al. (2022) compared infrared sauna to exercise directly in a randomised controlled crossover trial in Complementary Therapies in Medicine, finding meaningful cardiovascular and physiological responses that supported its use as an exercise-mimetic, particularly for populations who find traditional high heat difficult to tolerate. Growth hormone increased significantly in both traditional and infrared sauna conditions across multiple studies, with the magnitude varying by protocol.

The practical conclusion: both produce genuine physiological benefits. Steam delivers a stronger acute cardiovascular response and is supported by the longest-running longitudinal data. Infrared delivers deeper tissue penetration at a more accessible temperature. You now have both available. Choose based on your goal for that session.

Endorphins, mood and the neuroscience of heat

The pleasant, relaxed state that follows a sauna session is not just subjective. It has a neurochemical basis. Heat stress triggers the release of beta-endorphins, the endogenous opioid peptides that produce analgesia and mood elevation. Przewlocki (2016) reviewed opioid peptide physiology comprehensively in Neuroscience in the 21st Century, documenting the role of beta-endorphins in both pain modulation and mood regulation.

BDNF, brain-derived neurotrophic factor, increases following sauna sessions. Colucci-D'Amato, Speranza and Volpicelli (2020) reviewed BDNF's physiological functions in the International Journal of Molecular Sciences, finding that BDNF supports neuroplasticity, protects against depression and supports long-term brain health. The heat-induced BDNF increase is one mechanism through which regular sauna use may exert its documented effects on mood, cognitive function and mental wellbeing.

Yin et al. (2014) characterised neurochemical properties of BDNF-containing neurons in the ventrolateral periaqueductal gray, a brain region central to both pain modulation and emotional regulation. The connection between heat, BDNF and this region helps explain why regular sauna users consistently report improvements in mood, pain tolerance and stress resilience that outlast the session itself.