Sauna

What it is

A sauna session is a short exposure to dry heat. Finnish-style saunas were used at about 79 to 90 °C in the studies cited here [1][2], and infrared saunas at about 60 °C in a heart failure review [3].

How it might work

A 2019 review proposes that regular sauna use may help the heart and blood vessels by reducing arterial stiffness, inflammation and oxidative stress, steadying the autonomic nervous system, improving blood lipids and lowering blood pressure. These pathways are proposed by the authors and are not confirmed [4]. In 2,084 men aged 42 to 60, more frequent sauna use was linked to lower C-reactive protein, a blood marker of inflammation [5].

What the research says

The strongest findings come from the Kuopio Ischaemic Heart Disease study in eastern Finland. Among 2,315 middle-aged men followed for about 21 years, those who used the sauna 4 to 7 times a week had a hazard ratio of 0.37 for sudden cardiac death compared with men who went once a week; sessions over 19 minutes were linked to a hazard ratio of 0.48 compared with sessions under 11 minutes [6]. In 1,688 men and women aged 53 to 74, 4 to 7 weekly sessions were linked to a hazard ratio of 0.23 for fatal cardiovascular disease after adjustment for risk factors [7]. In the same cohort, men with both high fitness and frequent sauna use had the lowest sudden cardiac death risk (hazard ratio 0.31) [8]. In a related analysis of 2,277 men, frequent use (3 to 7 sessions a week) was linked to hazard ratios of 0.74 for cardiovascular death and 0.84 for all-cause death, and men with both good fitness and frequent sauna use had the lowest risks (0.42 and 0.60) [9]. A hazard ratio below 1 means fewer events in the group that used the sauna more often.

In 1,628 Finnish adults aged 53 to 74 without a prior stroke, 4 to 7 weekly sessions were linked to a stroke hazard ratio of 0.38 over about 15 years, after adjusting for risk factors, physical activity and social status [10].

In 2,315 of the same men, 4 to 7 weekly sessions were linked to a dementia hazard ratio of 0.34 over about 21 years; the Alzheimer's disease estimate was 0.35, with a wide range, and 2 to 3 sessions a week did not clearly differ from once a week [11]. In 2,575 men from the same study, frequent use (3 to 7 sessions a week) was linked to a hazard ratio of 0.86 for all-cause death [12].

For blood pressure, a 2021 meta-analysis of 15 studies of heat therapy, with sessions of 30 to 90 minutes over 10 to 36 sessions, found systolic pressure 3.94 mmHg lower and diastolic 3.88 mmHg lower than control [13]. A 2025 review of 20 randomised trials of passive heating found no clear pooled effect on most markers; the systolic pressure reduction was significant only with whole-body heating (4.11 mmHg lower), with high heterogeneity [14]. In a 47-person trial, adding a 15-minute sauna after exercise lowered systolic pressure by 8.0 mmHg more than exercise alone over 8 weeks [15].

In heart failure, a 2018 meta-analysis of infrared sauna studies found that 5 sessions a week for 2 to 4 weeks was linked to lower B-type natriuretic peptide, a marker of heart strain, and a higher left ventricular ejection fraction, with no change in blood pressure; the authors rated the evidence from moderate to insufficient [3]. A pilot study without a control group, in 18 people with heart failure and preserved pumping function, found better peak oxygen uptake (a fitness measure) and longer 6-minute walks after 10 weeks of sauna; some of the gain faded three months after stopping, and no adverse events were reported [16].

Blood vessel results are mixed. A meta-analysis found flow-mediated dilation, a test of how well an artery widens, improved by 1.95%, but rated the certainty of that result as low [13]. A 2025 review of 20 randomised trials found no significant pooled effect on flow-mediated dilation [14]. An 8-week trial in 41 adults with coronary artery disease, using four Finnish sauna sessions a week, found no change in artery dilation, arterial stiffness or blood pressure [1].

In a 37-person trial, adults with chronic tension-type headache who used a sauna regularly for 8 weeks had less headache pain than a control group that received advice only, with a between-group difference of 1.27 on the pain rating scale; sleep disturbance and depression did not change significantly [17].

In 16 male basketball players, one infrared sauna session after resistance training led to less muscle soreness than passive rest, and a smaller drop in jump performance measured about 14 hours later [18].

In an online survey of 482 regular sauna users, relaxation and stress relief were among the main reasons given for sauna use, and 83.5% reported sleep benefits; these are self-reports, not measured results [19]. A 2025 trial of 38 sedentary adults found that adding a 15-minute sauna after exercise did not improve heart rate variability beyond exercise alone [20].

Doses used in studies

These are doses used in studies, not recommendations. Finnish sauna at 79 °C with 13% humidity, 20 to 30 minutes, four times a week for 8 weeks, in adults with coronary artery disease [1]. Finnish sauna at 80 to 90 °C, 15 minutes, twice a week for 3 months, in 10 men [2]. Infrared sauna at 60 °C for 15 minutes, five times a week for 2 to 4 weeks, in heart failure studies [3]. Sauna at 60 °C, twice a week, with sessions rising from 8 to 15 minutes, for 10 weeks in the heart failure pilot [16]. Infrared sauna at about 43 °C (plus or minus 5) as a single session after resistance training [18]. A 15-minute sauna after exercise, for 8 weeks [15]. Regular sauna for 8 weeks in the headache trial; session details are not given in the abstract [17].

Safety and interactions

Common side effects: in an online survey of 482 regular users, adverse reactions were mostly minor (93.1%), mainly dizziness, dehydration and headache; two people needed hospital care, for chest pain and eye irritation [19]. Dehydration showed up in these reports, and sweat rate rose in the coronary artery trial [1].

Injuries: in a trauma centre series of 209 patients injured in saunas, the 274 injuries diagnosed were most often caused by slips and falls (57.5%) and dizziness or fainting (30.0%); fainting was most often linked to head and face injuries, and 9 patients (4.3%) needed surgery. The authors suggest drinking water before and after each session [21].

Alcohol: one patient in that series, with a blood alcohol level of 3.6 per mille, was burned while unconscious in the sauna [21]. A review notes that the few reports linking sauna with sudden cardiac death are single cases, attributed to dehydration, low blood pressure or heart rhythm problems, and some involved alcohol [4].

Medicines and heart conditions: a review found that sauna bathing was not particularly risky for people with hypertension, coronary heart disease or heart failure when medicated and stable, but blood pressure medicines may cause low blood pressure after a bath [22]. A later review says sauna is generally safe for most healthy people and for people with stable heart disease if used sensibly and with caution [4]. People with unstable heart disease, low blood pressure or fainting spells should ask a doctor first.

Pregnancy: a 2019 systematic review of 12 studies (347 pregnant women) found that sitting in a 40 °C bath or a 70 °C dry sauna for up to 20 minutes kept core temperature below 39 °C, the threshold for maternal overheating linked to birth defects [23]. An older narrative review found no adverse effects of bathing in pregnancy other than toxaemia cases [22]. Pregnant women should ask a doctor first. No data on breastfeeding were found.

Men's fertility: in 10 men who used a Finnish sauna twice a week for 3 months, sperm count and motility were significantly lower at the end of that period (P < 0.001). The changes were fully reversed six months after stopping [2].

Upper limits: the studies read here did not set a maximum session length. The only explicit time limit found is the 20-minute figure for pregnancy [23]. No data were found for children, or for people with kidney, liver or bleeding disorders.

Caveats and open questions

Most of the heart, stroke, dementia and death findings are observational. They show that frequent sauna users had fewer events, not that sauna caused the difference, and people who use saunas often may differ in fitness, income or other habits. Most of these results come from one Finnish study group, mainly of men [6][11].

The trials are small (16 to 47 people) and short (weeks). No trial measured deaths, strokes or dementia. Some results are null: the coronary artery trial found no change in artery function or blood pressure [1], and a heart rate variability trial found no added benefit over exercise [20].

Heat therapy in the blood pressure meta-analysis is a broader term than sauna, and its sessions ran 30 to 90 minutes [13]. Most heart failure evidence used infrared saunas, not Finnish saunas [3]. A 2025 review of 20 randomised trials of passive heating found no clear improvement in most cardiometabolic and vascular markers across trials, and flags high heterogeneity and limitations in the included studies [14].

Open questions: a trial of regular sauna for blood pressure in primary aldosteronism (NCT07796048) is not yet recruiting. The authors of the heart failure pilot describe a planned multicentre randomised trial [16]. Some of the cited studies report no conflicts of interest [3][20].

Sleep and relaxation: the headache trial found no significant change in sleep disturbance [17], and the reported sleep and relaxation benefits come from a survey, not a trial [19].