In 2023, López-Otín and colleagues published an updated framework identifying twelve hallmarks of aging, including genomic instability, telomere attrition, epigenetic alterations, loss of proteostasis, disabled macroautophagy, deregulated nutrient sensing, mitochondrial dysfunction, cellular senescence, stem cell exhaustion, altered intercellular communication, chronic inflammation, and dysbiosis[1]. These interconnected processes drive the progressive functional decline we experience as we age.

What makes thermal stress therapies so compelling from a longevity perspective is that they simultaneously target multiple hallmarks. Sauna use addresses loss of proteostasis (via heat shock proteins), chronic inflammation, cardiovascular decline, and disabled autophagy. Cold exposure targets mitochondrial dysfunction (via brown fat activation), deregulated nutrient sensing (via improved insulin sensitivity), and altered intercellular communication (via anti-inflammatory signaling). Together, they constitute one of the most accessible multi-target longevity interventions available.

The concept underlying both interventions is hormesis — the biological principle that controlled, low-dose stressors trigger adaptive responses that leave the organism stronger than before. Thermal stress, whether hot or cold, activates ancient cellular defense pathways that have been conserved across hundreds of millions of years of evolution.

When core body temperature rises during sauna bathing, cells activate a family of molecular chaperones known as heat shock proteins (HSPs). HSP70 and HSP90 are the most extensively studied. These proteins refold misfolded proteins, prevent toxic aggregation, and tag irreparably damaged proteins for degradation[6]. This process directly addresses the hallmark of “loss of proteostasis” — the age-related decline in the cell’s ability to maintain its protein quality control machinery.

Protein misfolding is central to neurodegenerative diseases. Alzheimer’s involves misfolded amyloid-beta and tau, Parkinson’s involves misfolded alpha-synuclein, and ALS involves misfolded SOD1. By upregulating HSPs, regular sauna use may provide neuroprotective effects. A prospective study of 2,315 Finnish men found that those using the sauna 4–7 times per week had a 65% lower risk of Alzheimer’s disease and a 66% lower risk of dementia compared to once-a-week users[4].

Patrick and Johnson (2021) published a comprehensive review in Experimental Gerontology arguing that sauna use should be considered a legitimate lifestyle practice for extending healthspan. They documented that regular heat stress activates FOXO3 — a longevity-associated transcription factor — increases expression of sirtuins, and triggers the Nrf2 antioxidant response pathway[5]. These are the same molecular targets that caloric restriction and exercise activate, establishing sauna use as a third pillar of hormetic longevity interventions.

A systematic review of clinical effects of regular dry sauna bathing confirmed improvements in cardiovascular function, pain management, chronic fatigue symptoms, and markers of oxidative stress[12]. The evidence is strongest for traditional Finnish saunas at 174–212°F (79–100°C) with sessions lasting 15–20 minutes.

Just as heat activates HSPs, cold exposure triggers the production of cold shock proteins — most notably RNA-binding motif protein 3 (RBM3). A landmark 2015 study published in Nature demonstrated that RBM3 mediates the structural plasticity and neuroprotective effects of cooling[7]. In mouse models of neurodegeneration, cooling-induced RBM3 expression prevented synapse loss and delayed disease progression. When RBM3 was blocked, the protective effects of cooling vanished entirely.

This finding has profound implications for human aging. Synapse loss is one of the earliest detectable changes in Alzheimer’s disease and correlates more strongly with cognitive decline than amyloid plaque burden. If cold exposure can stimulate RBM3 production in humans — and preliminary evidence suggests it can — then regular cold plunging may represent a practical strategy for preserving brain structure during aging.

Cold exposure also triggers a dramatic surge in norepinephrine — a neurotransmitter and hormone with potent anti-inflammatory properties. Immersion in 57°F (14°C) water increases plasma norepinephrine by 530%[13]. This catecholamine surge activates brown adipose tissue, enhances immune surveillance, and improves mood — all processes that deteriorate with age.

Cardiovascular disease remains the leading cause of age-related death worldwide. The strongest epidemiological evidence for thermal stress and longevity comes from the Kuopio Ischaemic Heart Disease (KIHD) study — a prospective cohort that followed 2,315 Finnish men for over 20 years. Men who used the sauna 4–7 times per week had a 63% lower risk of sudden cardiac death and a 40% lower risk of all-cause mortality compared to those who used it once per week[2].

A follow-up analysis confirmed that frequent sauna use was associated with reduced cardiovascular mortality in a dose-response manner, and the association held after adjusting for conventional risk factors including physical activity, socioeconomic status, and alcohol consumption[3].

The mechanisms are becoming clearer. Brunt et al. (2016) demonstrated that eight weeks of passive heat therapy (equivalent to sauna bathing) improved endothelial function, reduced arterial stiffness, and lowered blood pressure in sedentary adults[9]. Endothelial dysfunction is one of the earliest markers of vascular aging, and its reversal through heat therapy suggests that sauna use may functionally “de-age” blood vessels.

Cold exposure contributes complementary cardiovascular benefits. The repeated vasoconstriction and vasodilation that occur during contrast therapy serve as a form of vascular exercise, training blood vessels to respond more efficiently to hemodynamic demands. The Søberg et al. (2021) study on winter swimmers found enhanced cardiovascular and metabolic parameters in those who regularly alternated between sauna and cold water immersion[8].

Chronic, low-grade inflammation — often called “inflammaging” — is now recognized as a central driver of age-related disease[1]. Elevated levels of pro-inflammatory cytokines like IL-1β, IL-6, and TNF-α accelerate tissue damage, promote insulin resistance, and contribute to neurodegeneration. Both sauna use and cold exposure have demonstrated anti-inflammatory effects through distinct but complementary pathways.

Sauna bathing reduces C-reactive protein (CRP), a systemic marker of inflammation, in regular users. The HSP response triggered by heat stress also activates anti-inflammatory gene expression programs via the heat shock factor 1 (HSF1) transcription factor[5]. This dual action — reducing existing inflammation while building resistance to future inflammatory insults — makes sauna use a powerful tool against inflammaging.

Cold exposure contributes through the massive norepinephrine release described earlier. Norepinephrine suppresses TNF-α production by macrophages and shifts the immune system from a pro-inflammatory to an anti-inflammatory state[13]. Winter swimmers who combine sauna with cold immersion show lower baseline inflammatory markers than age-matched sedentary controls[12].

Autophagy — from the Greek for “self-eating” — is the cellular recycling process that clears damaged organelles, misfolded protein aggregates, and dysfunctional mitochondria. Disabled macroautophagy is now classified as a distinct hallmark of aging[1], and restoring autophagic function is considered one of the most promising anti-aging strategies.

Heat stress activates autophagy through multiple pathways. The AMPK pathway, which senses cellular energy status, is stimulated by the metabolic demands of thermoregulation during sauna use. Additionally, HSF1 directly upregulates autophagy-related genes[5]. The result is enhanced clearance of the cellular debris that accumulates with age and contributes to tissue dysfunction.

Cold exposure activates autophagy through complementary mechanisms. The norepinephrine surge stimulates SIRT1 — a longevity-associated deacetylase that promotes autophagy and mitochondrial biogenesis. Brown adipose tissue activation during cold exposure also demands extensive mitochondrial turnover, driving mitophagy (the selective autophagy of damaged mitochondria) in metabolically active tissues[10][11].

Cold acclimation also improves insulin sensitivity. Hanssen et al. (2015) showed that 10 days of cold acclimation improved insulin sensitivity by 43% in patients with type 2 diabetes[14]. Since insulin resistance is both a cause and consequence of impaired autophagy, this metabolic improvement creates a positive feedback loop that further enhances cellular housekeeping.

Based on the available evidence, a longevity-optimized thermal stress protocol should include both heat and cold exposure at frequencies and intensities shown to activate the protective pathways described above.

For a detailed step-by-step routine combining both modalities, see our Contrast Therapy Routine Guide or try the Hot Cold Coach App.

While thermal stress therapies have an excellent safety profile in healthy adults, they carry meaningful risks for certain populations. The acute cardiovascular demands of rapid temperature changes can trigger arrhythmias, syncope, or cardiac events in susceptible individuals[2].

Hydration is critical. Sauna bathing can cause fluid losses of 0.5–1.0 liters per session. Drink water before, during, and after sessions. Alcohol and sauna should never be combined — dehydration and impaired thermoregulation dramatically increase risk.

Never cold plunge alone. Cold shock response can cause involuntary gasping, loss of motor control, and in extreme cases, drowning. Always have a spotter present, use controlled environments, and enter the water gradually.