Safety

Who should be careful, and who should not start at all.

Heat and cold both put real load on the heart and blood vessels. These are the contraindications and cautions that appear in the medical literature. Review them with your doctor before you begin.

Sauna and heat therapy

Sauna bathing is well tolerated by most healthy adults and by people with stable, treated cardiovascular disease, and serious harm is uncommon given how widely it is used. In forensic series, most sauna deaths, burns and bath drownings involve alcohol or sedating drugs, bathing alone, or a long stay after losing consciousness. The literature identifies specific cautions: unstable heart disease and severe aortic stenosis; early pregnancy, where maternal hyperthermia and hot tub use are associated with neural tube defects and miscarriage while sauna-specific data are limited and largely reassuring; reversible falls in sperm quality; heat-sensitive neurological disease such as multiple sclerosis; hot-water reflex epilepsy; transdermal and other heat-sensitive medicines; and young children, who need supervision. Hot tubs add drowning, slip and water-borne infection risks, and poorly vented wood-fired steam baths can expose users to carbon monoxide.

Contraindications and cautions

Contraindicated: unstable angina pectoris, recent myocardial infarction, severe aortic stenosis (Hannuksela 2001, PMID 11165553).
Stable coronary disease, old MI, treated hypertension and stable heart failure are generally tolerated when medicated and stable (PMIDs 11165553, 16871826), but sauna produced silent scintigraphic ischemia in 14 of 15 stable coronary patients (PMID 10492315); a 15-min hot tub at 104 F caused no ischemia in stable coronary disease (PMID 8417250). Individual cardiology judgment applies.
Blood pressure: systolic pressure falls about 11-27 mmHg within 24 h of heat exposure, possibly more with beta blockers (PMID 41794190); a 10-min hot tub at 104 F was tolerated in treated hypertension (PMID 14662661). Antihypertensives and diuretics may predispose to orthostatic hypotension after bathing (PMID 16871826); rise slowly, sit before standing and rehydrate.
Implanted cardiac devices: electrical interference from a hot tub motor triggered an inappropriate defibrillator shock (case report, PMID 30177327).
Alcohol: avoid before and during heat. Sauna plus heavy drinking caused marked hypotension (PMID 1588256); alcohol was present in 71% of Swedish sauna deaths tested (PMID 19749613), 76 of 103 Korean sauna deaths (PMID 29926439), most Finnish hyperthermia deaths (PMID 1882775), about half of Finnish sauna deaths (PMID 18471223) and 40% of sauna burns (PMID 11834331). Do not bathe alone (PMID 19749613).
Medicines: heat increases absorption of transdermal and subcutaneous drugs such as nicotine, nitroglycerin and insulin (PMIDs 9571303, 8841153); a death in a sauna was attributed to a fentanyl patch (PMID 32740103). Lithium intoxication has been reported with saunas and dieting (PMID 589230). Sedatives and alcohol were found in most adult bath and hot tub drownings (PMID 40591495). Review heat-sensitive and narrow-margin drugs with the prescriber.
Overheating and heat stroke: most Finnish hyperthermia deaths occurred in saunas (PMID 1882775); heat stroke with multiorgan failure after prolonged sauna is reported (PMID 39773956); in Japanese bath emergencies, impaired consciousness tracked body temperature and most cardiac arrests were found face-down in the water (PMID 30146565). Keep sessions short and leave at the first dizziness or confusion.
Burns and falls: sauna contact burns are small but deep, with 36.6% needing surgery (PMID 37005140); hot-air burns after losing consciousness carried 50% mortality in one series (PMID 16046074). Slips and syncope cause most sauna injuries (PMID 37211472) and most hot tub injuries (PMID 19944920).
Pregnancy: maternal hyperthermia in early pregnancy is associated with neural tube defects (OR 1.92, PMID 15703536), and early hot tub use with miscarriage (aHR 2.0, PMID 14607798) and anencephaly and gastroschisis (PMID 21648056). Sauna-specific data are limited and largely reassuring (PMIDs 7112434, 1640616), and core temperature stayed below 102.2 F (39.0 C) with up to 20 min in a 158 F sauna (PMID 29496695). Avoid raising core temperature toward 102.2 F in the first trimester, and avoid prolonged hot tub use, unless an obstetric clinician advises otherwise.
Male fertility: regular sauna reversibly lowered sperm count and motility, recovering within 6 months (PMIDs 23411620, 9972494); stopping hot tub use improved motile sperm counts in some infertile men (PMID 17335598); male sauna use showed little association with time to conception (PMID 35924639). Men being evaluated for infertility may reasonably pause heat exposure.
Children: supervise closely. Blood pressure fell after heat in children under 10, with two vasovagal collapses (PMID 2371104), and one child had a 3.3-second sinus arrest (PMID 1709773), although habitual Finnish child bathing caused few, mild symptoms (PMID 2612514). Unsupervised access and suction entrapment drive child drownings in hot tubs and spas (PMIDs 2327545, 1853995).
Epilepsy: hot-water immersion can trigger reflex seizures (PMIDs 3451223, 1344769), and seizure disorders were a leading risk factor in spa and hot tub deaths (PMID 1853995). People with epilepsy should not bathe or soak alone.
Multiple sclerosis and other heat-sensitive neurological conditions: heat transiently worsens walking, balance and processing speed (PMIDs 22647586, 21914688); 73% of people with MS in a registry reported temperature sensitivity (PMID 42501584). Prolonged deficits after a hot bath test (PMID 6600798) and a fatal hyperthermia in a person unable to leave a hot bath (PMID 10990274) are reported.
Hot tub infections: hot tub lung from Mycobacterium avium complex (PMID 16194601), Legionnaires disease from poorly maintained hot tubs (PMID 39446669) and Pseudomonas folliculitis (PMID 2107063). Disinfection and maintenance matter most; immunocompromised patients warrant extra caution.
Carbon monoxide: wood-fired steam baths averaged 431-661 ppm CO with carboxyhemoglobin of 12-14% in adults and children (PMIDs 21618942, 21687856), and CO poisoning appears among Swedish sauna deaths (PMID 19749613). Fuel-fired heaters must be vented to the outside.
Psychotropic medication and severe mental illness: heat-related illness rises during heatwaves in these groups regardless of prescription (PMID 39648665); antipsychotics can impair thermoregulation (case report PMID 31157624).
Eyes: acute corneal hydrops in keratoconus (PMID 2763821) and intraocular pressure spikes in severe glaucoma (PMID 39845457) have followed sauna use (case reports).
Skin: sweating can provoke itch in atopic dermatitis and heat can trigger cholinergic urticaria (PMID 3218900). Sauna from day 3 after hernia repair did not impair wound healing in a randomized trial (PMID 12841561).
Reactive airways: cold air or cold showers after sauna may trigger bronchospasm (PMID 2281065).
General heat intolerance, acute febrile illness, dehydration, recent heavy exercise in heat, and inability to leave the sauna unaided (e.g. cognitive impairment, intoxication) call for avoidance or supervision.

Sources (56)

Systematic reviewMixed

Benefits and risks of sauna bathing.

Hannuksela ML et al. Am J Med. 2001. PubMed 11165553 · DOI

Who: review of sauna physiology, benefits and risks
What: sauna bathing
Measured: safety and contraindications
Result: Contraindications include unstable angina pectoris, recent myocardial infarction and severe aortic stenosis; sauna safe for most with stable angina or old MI; alcohol increases risk of hypotension, arrhythmia and sudden death; sweating may increase itch in atopic dermatitis; safe in uncomplicated pregnancy of healthy women.
Limitations: narrative review; no quantitative synthesis

Systematic reviewMixed

Cardiovascular and Other Health Benefits of Sauna Bathing: A Review of the Evidence.

Laukkanen JA et al. Mayo Clin Proc. 2018. PubMed 30077204 · DOI · Free full text

Who: review of observational studies and trials through February 2018
What: Finnish sauna bathing
Measured: cardiovascular and other outcomes; clinical implications
Result: Summarizes epidemiological, experimental and interventional evidence and implications for clinical practice; abstract reports no safety figures.
Limitations: narrative synthesis; much of the evidence from one Finnish cohort

Systematic reviewMixed

Health effects and risks of sauna bathing.

Kukkonen-Harjula K et al. Int J Circumpolar Health. 2006. PubMed 16871826 · DOI · Free full text

Who: literature review of sauna experiments (176-194 F, 5-20 min, 1-3 exposures)
What: sauna bathing
Protocol: 176-194 °F · 5-20 min
Measured: adverse effects, medications, pregnancy, children
Result: Well tolerated in healthy people; not particularly risky in stable, medicated hypertension, coronary disease or heart failure; antihypertensive medication may predispose to orthostatic hypotension after bathing; no adverse effects in pregnancy apart from toxemia cases.
Limitations: mostly uncontrolled studies in habitual bathers

Case series / reportHarm

Death in sauna.

Kenttämies A et al. J Forensic Sci. 2008. PubMed 18471223 · DOI

Who: deaths occurring in a sauna in Finland, 1990-2002
What: sauna bathing
Measured: death in sauna
Result: Annual rate under 2 per 100,000 inhabitants; 51% natural deaths, heat exposure the cause in 25%; 50% under the influence of alcohol.
Limitations: forensic series; total n not stated in abstract

Case series / reportn = 154Harm

Sauna-related burns: a review of 154 cases treated in Kuopio University Hospital Burn Center 1994-2000.

Papp A et al. Burns. 2002. PubMed 11834331 · DOI

Who: sauna-related burns at a Finnish burn centre, 1994-2000
What: sauna bathing
Measured: burn injury
Result: Sauna-related burns were one in four burn admissions; 54% required surgery; 40% of patients were under the influence of alcohol; estimated incidence 7 per 100,000.
Limitations: single centre; retrospective

Case series / reportn = 1Harm

Death in Sauna Associated With a Transdermal Fentanyl Patch.

Kriikku P et al. Am J Forensic Med Pathol. 2020. PubMed 32740103 · DOI · Free full text

Who: elderly woman using a transdermal fentanyl patch
What: sauna bathing while wearing a fentanyl patch
Measured: fatal opioid toxicity
Result: Found dead in the sauna with femoral blood fentanyl 15 micrograms/L; death attributed to fentanyl poisoning with external heat as contributing factor.
Limitations: single case report

Meta-analysisn = 39,617Harm

Maternal hyperthermia and the risk for neural tube defects in offspring: systematic review and meta-analysis.

Moretti ME et al. Epidemiology. 2005. PubMed 15703536 · DOI

Who: 15 studies (1,719 cases, 37,898 non-cases) of maternal hyperthermia in early pregnancy
What: maternal hyperthermia (any source)
Measured: neural tube defects
Result: Overall OR 1.92 (95% CI 1.61-2.29); case-control OR 1.93 (1.53-2.42); cohort RR 1.95 (1.30-2.92).
Limitations: hyperthermia sources pooled (fever, hot tub, sauna); observational

Prospective cohortn = 23,491Harm

Maternal heat exposure and neural tube defects.

Milunsky A et al. JAMA. 1992. PubMed 1640616

Who: pregnant women having alpha-fetoprotein screening or amniocentesis
What: hot tub, sauna, fever or electric blanket exposure in early pregnancy
Measured: neural tube defects
Result: Sauna: crude RR 2.6 (95% CI 0.7-10.1), adjusted RR 1.8 (0.4-7.9); hot tub adjusted RR 2.8 (1.2-6.5); two types of heat exposure RR 6.2 (2.2-17.2).
Limitations: sauna estimate imprecise and not statistically significant; self-reported exposure

Pilot / uncontrolled studyn = 42Harm

The effects of heat stress on physical functioning in persons with multiple sclerosis.

Romberg A et al. J Neurol Sci. 2012. PubMed 22647586 · DOI

Who: 23 heat-sensitive people with MS and 19 healthy controls
What: moderate heat exposure in a dry Finnish sauna
Measured: core temperature and physical function
Result: Core temperature rose more in MS than controls (P=0.002); walking (P<0.001), chair rise (P=0.005) and functional reach (P=0.04) worse immediately after heat; no prolonged effects.
Limitations: single exposure; heat-sensitive volunteers

Pilot / uncontrolled studyn = 42Harm

The effects of heat stress on cognition in persons with multiple sclerosis.

Hämäläinen P et al. Mult Scler. 2012. PubMed 21914688 · DOI

Who: 23 heat-sensitive people with MS and 19 healthy controls
What: moderate heat exposure in a Finnish sauna
Measured: cognition (PASAT, visual vigilance)
Result: Core temperature rose more in MS (p=0.002); PASAT 3-second performance worsened during heat (p=0.025), returning almost to baseline 1 h later; visual vigilance largely unaffected.
Limitations: single exposure; small

Case series / reportHarm

The role of psychotropics on the associations between extreme temperature and heat-related outcomes among people with mental health conditions: population-based study.

Wong AYS et al. Psychol Med. 2024. PubMed 39648665 · DOI · Free full text

Who: people with severe mental illness or depression in Japanese claims data, 2014-2021 (self-controlled case series)
What: heatwave exposure, with and without psychotropic prescription
Measured: heat-related illness
Result: Heat-related illness during heatwaves: SMI with vs without antipsychotics IRR 1.48 (1.40-1.56) vs 1.45 (1.35-1.56); depression with vs without antidepressants IRR 1.54 (1.46-1.64) vs 1.64 (1.57-1.71).
Limitations: environmental heat, not sauna; claims data; n not given in abstract

Systematic reviewn = 347No effect

Heat stress and fetal risk. Environmental limits for exercise and passive heat stress during pregnancy: a systematic review with best evidence synthesis.

Ravanelli N et al. Br J Sports Med. 2019. PubMed 29496695 · DOI

Who: 12 studies of pregnant women at any gestation exposed to exercise or passive heat (hot baths, sauna)
What: exercise or passive heat stress, including hot-water bathing at 104 F and dry sauna at 158 F
Protocol: 104 (bath); 158 (sauna) °F · up to 20 min
Measured: maternal core temperature relative to the 102.2 F (39.0 C) teratogenic threshold
Result: No woman exceeded a core temperature of 102.2 F (39.0 C); highest individual 102.0 F (38.9 C) during land exercise. Mean end-trial core temperature 98.4 F (36.9 C) for hot-water bathing and 99.7 F (37.6 C) for sauna. Authors conclude hot baths (104 F) or dry sauna (158 F) for up to 20 min did not reach the threshold at any stage of pregnancy.
Limitations: 12 small studies; core temperature is a surrogate, not fetal outcome; sauna data limited

Prospective cohortn = 1,063Harm

Hot tub use during pregnancy and the risk of miscarriage.

Li DK et al. Am J Epidemiol. 2003. PubMed 14607798 · DOI

Who: pregnant women in a Kaiser Permanente population-based cohort, 1996-1998
What: hot tub or whirlpool bath use after conception
Measured: miscarriage before 20 weeks
Result: Hot tub or whirlpool use after conception: adjusted HR 2.0 (95% CI 1.3-3.1); HR 1.7 for <1/week, 2.0 for 1/week, 2.7 for >1/week; HR 2.3 when first use was within 4 weeks of the last menstrual period.
Limitations: self-reported exposure; possible confounding by other behaviours; 1063 of 2729 eligible interviewed

Case-controln = 17,620Harm

Maternal use of hot tub and major structural birth defects.

Duong HT et al. Birth Defects Res A Clin Mol Teratol. 2011. PubMed 21648056 · DOI

Who: 10,825 mothers of infants with birth defects and 6,795 control mothers (US National Birth Defects Prevention Study, 1997-2005)
What: any hot tub use in early pregnancy
Measured: 17 types of major structural birth defects
Result: Any hot tub use: gastroschisis adjusted OR 1.54 (95% CI 1.10-2.17), anencephaly 1.68 (1.05-2.70). More than one use lasting over 30 min: ORs of 2.0 or more for esophageal atresia, omphalocele and gastroschisis; non-significant elevations for spina bifida and anencephaly.
Limitations: multiple comparisons and small cell sizes acknowledged by authors; recall of exposure

Case-controln = 302No effect

Sauna and congenital defects.

Saxén L et al. Teratology. 1982. PubMed 7112434 · DOI

Who: 100 cases of central nervous system defects and 202 orofacial clefts from the Finnish Registry of Malformations, with matched referents
What: maternal sauna bathing in pregnancy
Measured: CNS defects and orofacial clefts
Result: No differences in sauna habits between case and referent mothers; authors conclude the mild hyperthermia of Finnish sauna should not be considered hazardous to the embryo.
Limitations: near-universal exposure limits contrast; n of referents not stated in abstract; 1982 data

Pilot / uncontrolled studyn = 10Harm

Seminal and molecular evidence that sauna exposure affects human spermatogenesis.

Garolla A et al. Hum Reprod. 2013. PubMed 23411620 · DOI

Who: normozoospermic men
What: Finnish sauna, 2 sessions/week for 3 months
Protocol: 176-194 °F · 15 min · 2/wk · 12 wk
Measured: sperm count, motility, chromatin and gene expression; reversibility
Result: Strong impairment of sperm count and motility at the end of sauna exposure (P<0.001) with reduced chromatin condensation and mitochondrial function; no change in sex hormones; all effects completely reversed 6 months after stopping.
Limitations: uncontrolled; n=10; normozoospermic volunteers only

Pilot / uncontrolled studyHarm

Effects of sauna on sperm movement characteristics of normal men measured by computer-assisted sperm analysis.

Saikhun J et al. Int J Androl. 1998. PubMed 9972494 · DOI · Free full text

Who: normal men
What: sauna exposure for 2 weeks
Protocol: 2 wk
Measured: sperm movement (computer-assisted sperm analysis) and semen parameters
Result: Average path velocity, curvilinear velocity and lateral head displacement fell (p<0.01) after 2 weeks of sauna and returned to baseline within 1 week of stopping; volume, count, motility, morphology and penetration assay unchanged.
Limitations: small; n not stated in abstract; short exposure

Case series / reportn = 11Harm

Wet heat exposure: a potentially reversible cause of low semen quality in infertile men.

Shefi S et al. Int Braz J Urol. 2007. PubMed 17335598 · DOI · Free full text

Who: infertile men with regular wet-heat exposure (hot tubs, hot baths, whirlpools)
What: discontinuation of wet heat exposure
Measured: total motile sperm count after stopping heat exposure
Result: 5 of 11 (45%) responded, with a mean 491% increase in total motile sperm count; motility rose from 12% to 34% (p=0.02). Non-responders had more smoking pack-years.
Limitations: small uncontrolled series; selection of infertile men

Prospective cohortn = 3,041No effect

Male personal heat exposures and fecundability: A preconception cohort study.

McKinnon CJ et al. Andrology. 2022. PubMed 35924639 · DOI · Free full text

Who: couples trying to conceive in the US and Canada (preconception cohort, 2013-2021)
What: male self-reported heat exposures (sauna, hot bath/tub, seat heaters, laptop, tight underwear)
Measured: fecundability (per-cycle probability of conception)
Result: Little association for male sauna use. Hot bath/tub use 3 or more times/month vs none: fecundability ratio 0.87 (95% CI 0.70-1.07). Four or more heat exposures vs none: FR 0.77 (0.50-1.17); in men aged 30 or more, 0.60 (0.34-1.04).
Limitations: self-reported exposure; estimates imprecise

Systematic reviewMixed

Heat exposure and drugs. A review of the effects of hyperthermia on pharmacokinetics.

Vanakoski J et al. Clin Pharmacokinet. 1998. PubMed 9571303 · DOI

Who: review of human pharmacokinetic studies under heat exposure
What: external heating including sauna and steam baths
Measured: drug absorption and elimination
Result: Effects of heat on orally given drugs studied (midazolam, ephedrine, propranolol, tetracycline) were minor; absorption of transdermal and subcutaneous drugs (insulin, nitroglycerin, nicotine) is in most cases increased, raising plasma concentrations.
Limitations: narrative review; limited human data

Crossover trialn = 12Harm

Exposure to high ambient temperature increases absorption and plasma concentrations of transdermal nicotine.

Vanakoski J et al. Clin Pharmacol Ther. 1996. PubMed 8841153 · DOI

Who: healthy smokers using a transdermal nicotine patch
What: sauna, three 10-min periods at a mean 180 F, vs control session
Protocol: 180 °F · 30 (3 x 10) min
Measured: plasma nicotine pharmacokinetics
Result: Sauna significantly increased peak plasma nicotine, AUC 0-1 h and the amount absorbed (p<0.01 vs control); AUC 0-3 h not different; no adverse symptoms recorded.
Limitations: single session; healthy volunteers

Crossover trialn = 10Harm

Alcohol and sauna bathing: effects on cardiac rhythm, blood pressure, and serum electrolyte and cortisol concentrations.

Roine R et al. J Intern Med. 1992. PubMed 1588256 · DOI

Who: healthy men
What: sauna bathing with and without heavy alcohol intake
Measured: cardiac rhythm, blood pressure, electrolytes
Result: Sauna plus alcohol lowered systolic blood pressure from 136 +/- 4 to 113 +/- 3 mmHg (P<0.01), whereas sauna alone did not; neither condition increased premature ventricular complexes.
Limitations: small; young healthy men

Case series / reportHarm

Lithium intoxications induced by dieting and saunas.

Tonks CM et al. Br Med J. 1977. PubMed 589230 · DOI · Free full text

Who: patients taking lithium
What: dieting and sauna use
Measured: lithium intoxication
Result: Abstract not available; listed for completeness. The title reports lithium intoxications induced by dieting and saunas.
Limitations: no abstract; case reports; 1977

Case series / reportn = 77Harm

Sauna deaths in Sweden, 1992-2003.

Rodhe A et al. Am J Forensic Med Pathol. 2008. PubMed 19749613 · DOI

Who: sauna-related deaths in Sweden, 1992-2003 (national medicolegal autopsy database)
What: sauna bathing
Measured: cause and circumstances of death
Result: 82% men; 49 of 69 tested (71%) had positive blood alcohol, often high; 34 deaths (44%) alcohol-related and 18 (23%) cardiovascular; other causes included drowning, carbon monoxide poisoning and burns. All but 2 of those found dead in a sauna were alone.
Limitations: forensic series; no denominator of bathers

Case series / reportn = 103Harm

Characteristics of sauna deaths in Korea in relation to different blood alcohol concentrations.

Yang KM et al. Forensic Sci Med Pathol. 2018. PubMed 29926439 · DOI · Free full text

Who: sauna deaths in Korea, 2008-2015 (national forensic data)
What: sauna bathing
Measured: characteristics by blood alcohol concentration
Result: 76 of 103 decedents had blood alcohol of 0.08% or more. Intoxicated decedents were more often male (OR 17.4, 95% CI 3.8-79.8) and found prone (OR 11.3, 2.1-60.1); coronary narrowing and obesity did not differ by alcohol status.
Limitations: forensic series; no denominator

Case series / reportn = 228Harm

Hyperthermia deaths in Finland in 1970-86.

Kortelainen ML et al. Am J Forensic Med Pathol. 1991. PubMed 1882775 · DOI

Who: all deaths with hyperthermia as the underlying cause in Finland, 1970-1986
What: heat exposure, mostly sauna
Measured: hyperthermia death
Result: Most hyperthermia deaths occurred during sauna bathing, mostly in men aged 42-62; acute alcohol consumption was detected in most victims, some with chronic heavy drinking.
Limitations: death-certificate data; proportions not given in abstract

Case series / reportn = 158Harm

The health hazards of saunas and spas and how to minimize them.

Press E et al. Am J Public Health. 1991. PubMed 1853995 · DOI · Free full text

Who: US deaths in saunas, spas and hot tubs reported by medical examiners and the Consumer Product Safety Commission
What: sauna, spa or hot tub use
Measured: death and risk factors
Result: 7 of 158 deaths occurred in saunas, the rest in spas and hot tubs. Alcohol, heart disease, seizure disorders and cocaine accounted for 44.7% of deaths (alcohol 38%, heart disease 31%, seizures 17%, cocaine 14% of these). 61 of 151 spa deaths were children under 12, mainly drowning in uncovered spas or suction entrapment.
Limitations: voluntary reporting; 1991

Case series / reportn = 195Harm

Drugs and Drowning: The Toxicology of Adult Drownings in Baths and Hot Tubs in Australia, 2015-2024.

Darke S et al. Drug Alcohol Rev. 2025. PubMed 40591495 · DOI · Free full text

Who: all adult drowning deaths in baths or hot tubs in Australia, 2015-2024 (coronial data)
What: bath or hot tub immersion
Measured: toxicology and circumstances of drowning
Result: Psychotropic drug detected in 152 of 179 tested (84.9%), most often hypnosedatives (43.0%) and alcohol (41.9%); a preceding medical episode such as seizure or cardiac event in 16.9%; 87.7% of deaths were in a bath rather than a hot tub.
Limitations: mostly ordinary baths; includes intentional deaths (37.4%)

Cross-sectional studyn = 4,593Harm

Incidence and Characteristics of Bath-related Accidents.

Suzuki M et al. Intern Med. 2019. PubMed 30146565 · DOI · Free full text

Who: emergency calls related to bathing in three Japanese regions, Oct 2012-Mar 2013
What: hot-water (tub) bathing
Measured: bath-related cardiac arrest, illness and injury
Result: 4,593 events: 1,528 cardiac arrests, 935 survivors needing help, 1,553 acute illnesses, 577 injuries. Consciousness disturbance without organic disease was the main presentation; 30% of survivors had body temperature above 100.4 F (38 C), correlating with consciousness level; 79% of cardiac-arrest victims were found with the face submerged. Authors suggest heat illness during immersion leads to drowning.
Limitations: Japanese deep-tub bathing in older adults; surveillance design

Retrospective cohortn = 216Harm

Sauna contact burns in adults in the Helsinki Burn Centre during 2006-2018.

Valtonen J et al. Burns. 2023. PubMed 37005140 · DOI

Who: adults with sauna contact burns at the Helsinki Burn Centre, 2006-2018
What: sauna bathing
Measured: contact burn injury
Result: 71.8% men; older age associated with longer stay and surgery; burns were small but deep and 36.6% required surgery; over 40% occurred in summer.
Limitations: single referral centre

Case series / reportn = 6Harm

Rhabdomyolysis caused by hot air sauna burn.

Koski A et al. Burns. 2005. PubMed 16046074 · DOI

Who: consecutive patients with hot-air sauna burns
What: prolonged immobility in a hot sauna after heavy alcohol intake
Measured: burns, rhabdomyolysis, mortality
Result: All six lost consciousness after acute heavy drinking; third-degree burns of 5-32% body surface with rhabdomyolysis on admission; mortality 50% despite aggressive treatment.
Limitations: small series

Retrospective cohortn = 209Harm

Injuries related to sauna bathing.

Kaiser P et al. Injury. 2023. PubMed 37211472 · DOI · Free full text

Who: patients treated for sauna-related injuries at an Austrian trauma centre, 2005-2021
What: sauna bathing
Measured: injury type and cause
Result: 274 diagnoses: contusions/sprains 41.2%, wounds 28.8%, fractures 15.3%, concussions 5.5%, burns 1.5%, brain bleeding 1.1%. Causes: slip/fall 57.5%, dizziness/syncope 30.0%; head and face injuries mostly from syncope.
Limitations: single centre; no exposure denominator

Cross-sectional studyn = 81,597Harm

Hot tub, whirlpool, and spa-related injuries in the U.S., 1990-2007.

Alhajj M et al. Am J Prev Med. 2009. PubMed 19944920 · DOI

Who: US emergency department visits for hot tub, whirlpool and spa injuries, 1990-2007 (national weighted estimate)
What: hot tub, whirlpool or spa use
Measured: non-fatal injury
Result: Estimated 81,597 ED visits, rising 160% over the period (p<0.001); lacerations most common (27.8%); slips and falls the most common mechanism (47.6%) and associated with concussion and fractures.
Limitations: weighted national sample estimates; non-fatal only

Case series / reportn = 1Harm

Severe heat stroke with multiorgan failure following collapse in a sauna.

McIver WJ et al. BMJ Case Rep. 2025. PubMed 39773956 · DOI

Who: adult who collapsed after prolonged sauna use
What: prolonged sauna use
Measured: classical heat stroke
Result: Heat stroke with seizures, liver and kidney injury, disseminated intravascular coagulation, rhabdomyolysis and type 2 myocardial infarction; full recovery after external cooling, fluids and blood products.
Limitations: single case report

Crossover trialn = 16Harm

Sauna-induced myocardial ischemia in patients with coronary artery disease.

Giannetti N et al. Am J Med. 1999. PubMed 10492315 · DOI

Who: patients with proven stable coronary artery disease
What: sauna bathing vs exercise vs rest with sestamibi perfusion imaging
Measured: myocardial perfusion, ECG, blood pressure
Result: Sauna was clinically well tolerated with no arrhythmias or ECG changes, but perfusion defect scores worsened vs rest (-0.44 vs -0.93, P<0.001) in 14 of 15 patients; heart rate rose 32% and systolic pressure fell 13%.
Limitations: small; single session; scintigraphic ischemia without symptoms

Crossover trialn = 15No effect

Cardiovascular responses to immersion in a hot tub in comparison with exercise in male subjects with coronary artery disease.

Allison TG et al. Mayo Clin Proc. 1993. PubMed 8417250 · DOI

Who: men with clinically stable coronary artery disease
What: hot tub immersion at 104 F for 15 min vs 15 min cycle exercise
Protocol: 104 °F · 15 min
Measured: heart rate, blood pressure, ischemia, symptoms
Result: Peak heart rate lower in the hot tub than with exercise (85 vs 112 bpm), as was systolic pressure (106 vs 170 mmHg, P<0.01); tympanic temperature rose 1.1 F (0.6 C); no ischemic ECG changes or clinical complications.
Limitations: small; men only; single session

Controlled trial (not randomized)n = 44No effect

Are hot tubs safe for people with treated hypertension?

Shin TW et al. CMAJ. 2003. PubMed 14662661 · Free full text

Who: 21 adults with stable treated hypertension and 23 normotensive controls
What: hot tub immersion at 104 F for 10 min
Protocol: 104 °F · 10 min
Measured: blood pressure, heart rate, symptoms
Result: Systolic pressure fell from 144 to 122 mmHg in hypertensive and from 130 to 110 mmHg in control participants (both p<0.05) and returned toward baseline within 10 min; no dizziness, chest pain or palpitations.
Limitations: single short session; small

Systematic reviewMixed

Acute blood pressure responses and safety considerations in heat therapy interventions: A narrative review.

Yamasaki S et al. Complement Ther Med. 2026. PubMed 41794190 · DOI · Free full text

Who: 21 studies (2 RCTs, 1 crossover, 7 non-randomized, 11 observational) of adults aged 18-94
What: sauna, hot spring bathing, hot-water immersion, mudpacks
Measured: acute (24 h or less) blood pressure response and safety
Result: Systolic blood pressure fell by about 11-27 mmHg within 24 h across modalities; a few small studies suggested larger falls in beta-blocker users; serious acute adverse events were rare; safety margins in frail older adults and beta-blocker users remain insufficiently defined.
Limitations: narrative synthesis; most studies uncontrolled and heterogeneous

Case series / reportn = 1Harm

Inappropriate ICD shock due to hot tub-induced external electrical interference.

Shenasa M et al. J Electrocardiol. 2018. PubMed 30177327 · DOI

Who: patient with an implantable cardioverter-defibrillator
What: hot tub use
Measured: device behaviour
Result: Electrical interference from the hot tub motor (60-cycle artifact) was detected as ventricular fibrillation and triggered an inappropriate 34.8 J shock during sinus rhythm.
Limitations: single case report; device- and installation-specific

Case series / reportn = 2Harm

Hot-bath epilepsy.

Pall HS et al. Postgrad Med J. 1987. PubMed 3451223 · DOI · Free full text

Who: patients with reflex epilepsy
What: hot-bath immersion
Measured: seizures
Result: Two cases of reflex epilepsy triggered by immersion in hot baths.
Limitations: two cases

Case series / reportn = 1Harm

Hot-water epilepsy in an adult: ictal EEG, MRI and SPECT features.

Lisovoski F et al. Seizure. 1992. PubMed 1344769 · DOI

Who: 20-year-old man with hot-water epilepsy
What: hot-water immersion
Measured: ictal EEG and imaging
Result: Seizures specifically induced by hot-water immersion; ictal EEG during a hot bath showed focal left temporo-occipital discharges with matching hypometabolism on SPECT; MRI normal.
Limitations: single case

Case series / reportn = 1Harm

Fatal hyperthermia in hot baths in individuals with multiple sclerosis.

Kohlmeier RE et al. Am J Forensic Med Pathol. 2000. PubMed 10990274 · DOI

Who: 47-year-old man with multiple sclerosis
What: hot bath with continuous hot-water flow
Measured: fatal hyperthermia
Result: Found dead in a bathtub with body temperature 105.7 F and negative autopsy and toxicology; authors note heat-induced motor weakness in MS can prevent getting out of hot water.
Limitations: single forensic case

Case series / reportn = 4Harm

Persistent neurological deficit precipitated by hot bath test in multiple sclerosis.

Berger JR et al. JAMA. 1983. PubMed 6600798

Who: patients with multiple sclerosis undergoing the hot bath test
What: diagnostic hot bath
Measured: neurological deficit
Result: Four patients had considerable and prolonged neurological debilitation after hot bath testing, although heat-related worsening is usually transient.
Limitations: small series; diagnostic heating, not recreational use

Cross-sectional studyn = 760Harm

Keeping cool - how persons with MS manage heat sensitivity: Insights from the Swiss multiple sclerosis registry.

Iaquinto S et al. Mult Scler Relat Disord. 2026. PubMed 42501584 · DOI · Free full text

Who: people with multiple sclerosis in the Swiss MS Registry
What: survey of temperature sensitivity
Measured: prevalence of heat sensitivity and symptoms
Result: 73.3% reported temperature sensitivity, most commonly to heat (48.8%) or both heat and cold (18%); fatigue (70.2%), weakness (48.7%) and gait problems (38.6%) were the symptoms most often worsened.
Limitations: self-report survey; not sauna-specific

Pilot / uncontrolled studyn = 81Harm

Children in sauna: cardiovascular adjustment.

Jokinen E et al. Pediatrics. 1990. PubMed 2371104

Who: 61 children and 20 adolescents and young adults
What: 10-min heat exposure in a climatic chamber matching a Finnish sauna
Protocol: 10 min
Measured: circulatory adjustment
Result: Rectal temperature and heart rate rose in all (P<.001); blood pressure fell after exposure in children under 10 (P<.001) with two vasovagal collapses; stroke volume fell 32.9% in children under 5.
Limitations: laboratory chamber; single exposure

Pilot / uncontrolled studyn = 101Harm

Children in sauna: electrocardiographic abnormalities.

Jokinen E et al. Acta Paediatr Scand. 1991. PubMed 1709773 · DOI

Who: 81 children and 20 adolescents and young adults
What: heat exposure in a climatic chamber resembling a Finnish sauna
Measured: ECG changes
Result: Sympathetic-type ECG changes in 57% during and 23% after heat; extrasystoles in 3 children during and 4 after; a 5-year-old with wandering pacemaker had a 3.3-second sinus arrest. Changes were transient.
Limitations: laboratory chamber; single exposure

Cross-sectional studyn = 1,247No effect

Sauna habits and related symptoms in Finnish children.

Markkola L et al. Eur J Pediatr. 1989. PubMed 2612514 · DOI

Who: families of randomly chosen Finnish children aged 0-15
What: habitual sauna bathing
Protocol: 1-3/wk
Measured: symptoms during or after sauna
Result: 98.5% of children used the sauna; symptoms were rare and not serious, mostly transient dizziness or nausea; atopic dermatitis worsened in the sauna in half of affected children.
Limitations: parent questionnaire; healthy children

Case series / reportn = 74Harm

Young children who drown in hot tubs, spas, and whirlpools in California: a 26-year survey.

Shinaberger CS et al. Am J Public Health. 1990. PubMed 2327545 · DOI · Free full text

Who: drownings in hot tubs, spas and whirlpools in California, 1960-1985
What: hot tub, spa or whirlpool access
Measured: child drowning
Result: 74 deaths, mostly children under 2; drowning rate rose tenfold from 1967 to 1985; deaths were associated with unsupervised access, neuromotor handicaps and suction entrapment.
Limitations: historical surveillance data

Case series / reportn = 21Harm

Hot tub lung: presenting features and clinical course of 21 patients.

Hanak V et al. Respir Med. 2006. PubMed 16194601 · DOI · Free full text

Who: patients diagnosed with hot tub lung at a tertiary centre over 7 years
What: ongoing hot tub exposure
Measured: clinical course of hot tub lung (Mycobacterium avium complex)
Result: All had dyspnea and cough, 48% hypoxemia; centrilobular nodules or ground-glass opacities on CT; M. avium complex isolated in all; all improved with avoidance, 62% also received corticosteroids.
Limitations: retrospective single centre

Case series / reportn = 12Harm

Two Outbreaks of Legionnaires Disease Associated with Outdoor Hot Tubs for Private Use - Two Cruise Ships, November 2022-July 2024.

Lee S et al. MMWR Morb Mortal Wkly Rep. 2024. PubMed 39446669 · DOI · Free full text

Who: travelers on two cruise ships, 2022-2024
What: private balcony hot tubs
Measured: Legionnaires disease
Result: 12 cases of Legionnaires disease; epidemiologic and environmental sampling identified private cabin hot tubs as the most likely source; risk attributed to inadequate maintenance and operation.
Limitations: outbreak investigation

Systematic reviewHarm

Whirlpool folliculitis: a review of its cause, treatment, and prevention.

Berger RS et al. Cutis. 1990. PubMed 2107063

Who: review of whirlpool (Pseudomonas aeruginosa) folliculitis
What: hot tub and whirlpool use
Measured: folliculitis
Result: Follicular pustules and papules appear 2-4 days after exposure and usually resolve spontaneously in 7-10 days; prevention depends on water maintenance.
Limitations: brief narrative review

Cross-sectional studyn = 288Harm

Exposures to high levels of carbon monoxide from wood-fired temazcal (steam bath) use in highland Guatemala.

Thompson LM et al. Int J Occup Environ Health. 2011. PubMed 21618942 · DOI · Free full text

Who: users of 72 wood-fired temazcal steam baths in highland Guatemala
What: wood-fired steam bath use
Measured: carbon monoxide exposure
Result: Temazcal CO exposures averaged 431 ppm (time-weighted average) and contributed significantly to weekly CO exposure despite short use.
Limitations: specific traditional bath design; exposure measures

Pilot / uncontrolled studyHarm

Non-invasive measurement of carbon monoxide burden in Guatemalan children and adults following wood-fired temazcal (sauna-bath) use.

Lam N et al. J Environ Monit. 2011. PubMed 21687856 · DOI · Free full text

Who: Guatemalan children and adults after wood-fired temazcal use
What: wood-fired steam bath use
Measured: carboxyhemoglobin
Result: CO during use averaged 661 +/- 503 ppm, about 10 times the WHO 15-min guideline; average carboxyhemoglobin 12-14% (maximum 30%); children's levels did not differ from adults' despite 66% less time exposed.
Limitations: pilot; n not stated in abstract

Case series / reportn = 1Harm

Acute bilateral corneal hydrops caused by high temperature and high moisture in the Finnish sauna. A clinical and histological case report of a patient with keratoconus.

Ruusuvaara P et al. Acta Ophthalmol (Copenh). 1989. PubMed 2763821 · DOI

Who: 44-year-old man with bilateral keratoconus
What: hot, humid Finnish sauna
Measured: acute corneal hydrops
Result: Acute hydrops in each eye, 3 years apart, each the evening after a hot, humid sauna; both required penetrating keratoplasty.
Limitations: single case

Case series / reportn = 1Harm

Elevated intraocular pressure associated with sauna use: A case report.

Arguinchona LM et al. Am J Ophthalmol Case Rep. 2025. PubMed 39845457 · DOI · Free full text

Who: 64-year-old man with severe primary open-angle glaucoma
What: sauna sessions
Measured: intraocular pressure
Result: Intraocular pressure spikes after sauna sessions, confirmed by home tonometry, resolved after glaucoma surgery.
Limitations: single case

Randomized controlled trialn = 79No effect

Sauna-bathing with sutures. A prospective and randomised study.

Papp AA et al. Scand J Surg. 2003. PubMed 12841561 · DOI · Free full text

Who: patients after elective day-case hernioplasty
What: sauna allowed from postoperative day 3 vs sauna prohibited until suture removal
Measured: wound healing
Result: No difference in wound healing between groups; authors found no reason to prohibit sauna bathing with sutures in this group.
Limitations: single procedure type; abstract gives no event counts

Cold-water immersion

Brief, controlled cold-water immersion is tolerated by most healthy adults, but its acute hazards are real. Sudden immersion triggers the cold shock response within seconds: an inspiratory gasp, hyperventilation, tachycardia and a rise in blood pressure. In open water this response, rather than hypothermia, is thought to cause many immersion deaths, through aspiration, hypocapnia and arrhythmia, and simultaneous cold shock and diving response with face immersion and breath-holding ('autonomic conflict') is a proposed arrhythmia mechanism. Longer swims add hypothermia, with core temperature continuing to fall after leaving the water (afterdrop), and swimming-induced pulmonary edema, which is more common in older women and people with hypertension or heart disease. Transient global amnesia after cold-water swimming is reported in case series. The cold shock response habituates after about 4 immersions. Small studies in stable heart failure and coronary disease found cold immersion tolerated but with higher blood pressure and, in heart failure, more ventricular ectopy. Whole-body cryotherapy chambers are a separate modality with their own reported harms (frostbite, cold panniculitis, isolated vascular and neurological events) and a published contraindication list.

Contraindications and cautions

Never immerse alone: cold shock can incapacitate or cause death within seconds, before hypothermia (Tipton 1989, PMID 2691172; Leuci 2026, PMID 42532024). In occupational immersions, deaths occurred in water below 63.5 F, 95% below 59 F (PMID 15871996).
Avoid face immersion and breath-holding on entry; combined cold shock and diving response ('autonomic conflict') is a proposed arrhythmia mechanism (PMIDs 22547634, 16714416), and face immersion produced more ectopic beats than body immersion in adolescents (PMID 40624837). Arrhythmia is the most likely cause of swimming-related death in a systematic review (PMID 26941276).
Cardiovascular disease (coronary disease, heart failure, arrhythmia, channelopathy such as long QT): requires physician assessment; cold raises blood pressure, rate-pressure product and, in heart failure, ventricular ectopy (PMIDs 19696059, 26152773, 42532024). A prolonged cold swim pushed QTc above 500 ms in 5 of 20 healthy swimmers (PMID 39461093).
Uncontrolled hypertension: cold shock includes an acute pressor response (PMIDs 16714416, 26152773). No trial shows cold immersion lowers resting blood pressure.
Alternating sauna and cold water places greater strain on the heart than either alone (Kauppinen 1989, PMID 2736002).
Hypothermia and afterdrop: core temperature keeps falling for up to about 25 min after leaving cold water (PMIDs 11043627, 36754061); hypothermia was the most common illness in a long open-water race, with lean swimmers and longer swims at higher risk (PMID 19364182). Keep exposures short, rewarm actively and do not drive until rewarmed.
Swimming-induced pulmonary edema (cough, breathlessness, frothy or bloody sputum while swimming): associated with cold water (PMID 30410770) and with heart disease, hypertension, older age, female sex, asthma, recent respiratory infection and little open-water experience (PMID 41903839). Stop swimming and seek care if it occurs; prior episodes predict recurrence.
Transient global amnesia and other neurological events: reported after sea swimming (9 cases, PMID 40270669), during prolonged cold immersion (PMID 11990187) and after whole-body cryotherapy (PMID 29030365).
Raynaud's phenomenon (primary or secondary): cold triggers vasospastic digital ischemia; generally a contraindication to whole-body or extremity cold immersion (Ramahi 2022, PMID 35699336).
Cold urticaria: risk of anaphylaxis with water submersion (PMIDs 34437035, 37873787); an adrenaline auto-injector is advised for high-risk patients, including those whose urticaria follows cold-water immersion (PMID 37873787).
Pregnancy: no safety studies of cold plunge; cold pressor stimulus constricted the uterine artery in late pregnancy, more so with preeclampsia (Kimura 1998, PMID 10223611). Avoid unless cleared by the obstetric clinician.
Children: immersion in 52 F water raised children's heart rate 31% and breathing rate 58% (PMID 41602813); supervise closely and avoid face immersion (PMID 40624837).
Prolonged exposure leads to swimming failure (peripheral neuromuscular cooling impairs motor function at near-normal core temperature) and then hypothermia; keep exposures short and within the durations used in trials (PMID 42532024).
Alcohol and psychoactive substances increase immersion risk (PMID 42532024).
Gradual entry and repeated graded exposure blunt the cold shock response (PMIDs 38211547, 15778892); unaccustomed people carry the highest risk (PMID 33276648).
Peripheral neuropathy or impaired microvascular function (e.g., diabetes) may raise cold-injury risk (see type-2-diabetes entry).
Whole-body cryotherapy chambers are a separate modality: an expert consensus lists absolute and temporary contraindications (PMID 40303546). Reported harms include frostbite (PMID 35245366), cold panniculitis (PMID 29693065), abdominal aortic dissection (PMID 28829347), reversible cerebral vasoconstriction (PMID 41452070) and transient global amnesia (PMID 29030365); skin rash and itching were common in athletes (PMID 36927611). A scoping review judged risks acceptable when contraindications are followed (PMID 37770960). Cold-water safety data do not transfer.

Sources (36)

Systematic reviewHarm

The initial responses to cold-water immersion in man.

Tipton MJ et al. Clin Sci (Lond). 1989. PubMed 2691172 · DOI

Who: review of human cold-water immersion responses
What: cold-water immersion
Measured: cold shock response and immersion deaths
Result: Concludes the cold-shock response can cause death or serious incapacitation long before general hypothermia and is probably responsible for most annual open-water immersion deaths.
Limitations: narrative review; abstract is a brief conclusion only

Systematic reviewHarm

Respiratory responses to cold water immersion: neural pathways, interactions, and clinical consequences awake and asleep.

Datta A et al. J Appl Physiol (1985). 2006. PubMed 16714416 · DOI

Who: review of respiratory and cardiac responses to immersion
What: cold-water immersion
Measured: respiratory and arrhythmic responses
Result: Skin cooling elicits 'cold shock': an initial gasp, hypertension and hyperventilation despite profound hypocapnia, overriding voluntary breathing control and possibly precipitating drowning; apnea release with hypoxemia and simultaneous sympathetic and vagal stimulation appears arrhythmogenic.
Limitations: narrative review

Systematic reviewHarm

'Autonomic conflict': a different way to die during cold water immersion?

Shattock MJ et al. J Physiol. 2012. PubMed 22547634 · DOI · Free full text

Who: review of cardiac arrhythmias during cold-water submersion
What: cold-water submersion with breath-holding
Measured: arrhythmia mechanisms
Result: Cold-water submersion can induce a high incidence of arrhythmias in healthy volunteers; strong simultaneous activation of the sympathetic cold shock response and parasympathetic diving response ('autonomic conflict') is proposed as a cause of some deaths previously attributed to drowning or hypothermia, especially in individuals with predisposing conditions.
Limitations: hypothesis-generating review

Systematic reviewHarm

Beyond hypothermia: mechanisms of death, rescue, and prevention in cold water immersion.

Leuci L et al. J Appl Physiol (1985). 2026. PubMed 42532024 · DOI · Free full text

Who: review of cold-water immersion deaths
What: cold-water immersion
Measured: mechanisms of death
Result: Four-stage model: cold shock, swimming failure, hypothermia and circum-rescue collapse. Cold shock can kill via aspiration, hypocapnia-induced cerebral hypoperfusion and arrhythmia before core temperature falls; autonomic conflict and channelopathies are candidate mechanisms of sudden arrhythmic death; alcohol and psychoactive substances modify risk.
Limitations: narrative review

Meta-analysisn = 145Benefit

Habituation of the cold shock response: A systematic review and meta-analysis.

Barwood MJ et al. J Therm Biol. 2024. PubMed 38211547 · DOI · Free full text

Who: 17 groups of volunteers undergoing repeated cold-water immersion
What: repeated cold-water immersion
Measured: cold shock response habituation
Result: All cold shock variables habituated (p<0.001): heart rate -14 (10) bpm (d -1.19); respiratory frequency -8 (7) breaths/min (d -0.78); minute ventilation -21.3 (9.8) L/min (d -1.64).
Limitations: healthy volunteers; variation between studies

Pilot / uncontrolled studyn = 18Benefit

Repeated cold showers as a method of habituating humans to the initial responses to cold water immersion.

Eglin CM et al. Eur J Appl Physiol. 2005. PubMed 15778892 · DOI

Who: non-habituated healthy adults (13 men, 5 women)
What: six cold showers over 4 days (3 min at 50 F on the back; 3 min at 59 F on the back; or 30 s back + 30 s front at 50 F) before a 3-min head-out immersion in 50 F water
Protocol: 50-59 °F · 1-3 min
Measured: respiratory frequency and heart rate on immersion
Result: Showers at 50 F reduced respiratory frequency in the first 30 s of immersion by 21% (54 to 44 and 33 to 26 breaths/min, P<0.05); 59 F showers did not. Tachycardia was not reduced except in the 59 F group late in immersion.
Limitations: small; healthy volunteers; short-term

Prospective cohortn = 20No effect

Cardiac arrhythmia during cold-water immersion: a self-controlled field study with extended rhythm monitoring.

Merkt B et al. J Exerc Sci Fit. 2026. PubMed 42100593 · DOI · Free full text

Who: middle-aged recreational cold-water swimmers (mean age 56; 7 at high 10-year CV risk)
What: open-water cold-water immersion during an organized event, with 10-day ambulatory ECG
Protocol: 45 (mean) °F
Measured: arrhythmic burden
Result: Heart rate rose 40 +/- 13 bpm (43%) during immersion (p<0.001); one brief non-sustained atrial tachycardia during immersion; arrhythmia rates 0.12 vs 0.037 per hour during vs outside immersion (p=0.25); no sustained arrhythmias.
Limitations: small; self-selected experienced swimmers; single-lead ECG

Crossover trialn = 22Harm

Haemodynamic and arrhythmic effects of moderately cold (22 degrees C) water immersion and swimming in patients with stable coronary artery disease and heart failure.

Schmid JP et al. Eur J Heart Fail. 2009. PubMed 19696059 · DOI

Who: men with compensated heart failure (n=12, EF 32%, NYHA II) or stable coronary disease (n=10)
What: water immersion and swimming in moderately cold (72 F) vs warm (90 F) water
Protocol: 72 vs 90 °F
Measured: hemodynamics, arrhythmias
Result: Rate-pressure product during chest-deep immersion higher in 72 F than 90 F water (P=0.043 CHF, P=0.028 CAD). PVCs in heart failure rose from 15 +/- 41 to 76 +/- 163 per 30 min in 72 F water (P=0.013); no ventricular tachycardia.
Limitations: small; moderately cold, not plunge temperatures

Crossover trialn = 37Mixed

Acute effects of Finnish sauna and cold-water immersion on haemodynamic variables and autonomic nervous system activity in patients with heart failure.

Radtke T et al. Eur J Prev Cardiol. 2016. PubMed 26152773 · DOI

Who: men with chronic heart failure (n=12), coronary artery disease (n=13) and controls (n=12)
What: two Finnish sauna exposures at 176 F followed by head-out cold-water immersion
Protocol: 54 (immersion); 176 (sauna) °F
Measured: cardiac output, blood pressure, heart rate variability, arrhythmias
Result: Cold-water immersion significantly increased systolic blood pressure in all groups (p<0.05); cardiac output and heart rate rose; well tolerated, with no excessive adrenergic activation or complex arrhythmias.
Limitations: single session; small; stable selected patients

Crossover trialn = 9Harm

Sauna, shower, and ice water immersion. Physiological responses to brief exposures to heat, cool, and cold. Part II. Circulation.

Kauppinen K et al. Arctic Med Res. 1989. PubMed 2736002

Who: healthy men
What: sauna followed by head-out ice-water immersion, 59 F shower, or room temperature; ice-water immersion alone
Protocol: ice water; 59 (shower) °F
Measured: heart rate, blood pressure, peripheral resistance, cardiac work
Result: Cold exposure increased total peripheral resistance and stroke work; alternating heat with cold or cool water presented the most intensive strain on the heart.
Limitations: small; healthy men; 1989 methods

Systematic reviewHarm

Practical management of Raynaud's phenomenon - a primer for practicing physicians.

Ramahi A et al. Curr Opin Rheumatol. 2022. PubMed 35699336 · DOI · Free full text

Who: review for practicing physicians
What: n/a
Measured: Raynaud's phenomenon management
Result: Raynaud's phenomenon is a vasospastic condition causing digital hypoperfusion in response to cold and/or emotional stress, with significant pain and disability; secondary Raynaud's may signal systemic sclerosis.
Limitations: narrative review

Case series / reportn = 1Harm

Anaphylaxis Caused by Swimming: A Case Report of Cold-induced Urticaria in the Emergency Department.

McManus NM et al. Clin Pract Cases Emerg Med. 2021. PubMed 34437035 · DOI · Free full text

Who: 50-year-old man with recent cold-induced urticaria
What: jumping into a lake
Measured: anaphylaxis
Result: Anaphylaxis on lake immersion; authors note up to one-third of patients with cold urticaria can develop severe symptoms including anaphylaxis, particularly from water submersion such as swimming.
Limitations: single case report

Case-controlHarm

The effect of cold stress on uterine artery blood flow velocity waveforms in late pregnant women with and without preeclampsia.

Kimura Y et al. Tohoku J Exp Med. 1998. PubMed 10223611 · DOI · Free full text

Who: late-pregnancy women with and without preeclampsia
What: hand immersion in ice water (cold pressor stimulus)
Measured: uterine artery pulsatility index, fetal heart rate
Result: Uterine artery pulsatility index rose with cold stimulus (preeclampsia 1.14 to 1.52; controls 0.95 to 1.25); in 2 of 11 preeclampsia cases with growth restriction, fetal heart rate variability decreased. Authors: cold induces uterine artery constriction and lower placental blood flow.
Limitations: small; hand immersion only; sample sizes partly unstated in abstract

Meta-analysisn = 3,177Mixed

Effects of cold-water immersion on health and wellbeing: A systematic review and meta-analysis.

Cain T et al. PLoS One. 2025. PubMed 39879231 · DOI · Free full text

Who: healthy adults (11 randomized trials)
What: cold shower, ice bath or plunge at 45-59 F for 30 s to 2 h
Protocol: 45-59 °F · 0.5-120 min
Measured: inflammation and other outcomes
Result: Significant acute increase in inflammation immediately (SMD 1.03, 95% CI 0.37 to 1.68) and 1 h after cold-water immersion (SMD 1.26, 95% CI 0.59 to 1.94).
Limitations: healthy adults; few RCTs

Systematic reviewMixed

Cold Water Swimming-Benefits and Risks: A Narrative Review.

Knechtle B et al. Int J Environ Res Public Health. 2020. PubMed 33276648 · DOI · Free full text

Who: narrative review of cold-water (winter, ice) swimming
What: cold-water swimming
Measured: benefits and risks
Result: Health benefits appear when practiced by experienced, healthy people in a regular, graded way; risk of death in unaccustomed people from the initial cold shock response, progressive loss of swimming efficiency, or hypothermia.
Limitations: narrative review

Case series / reportn = 130Harm

How much did cold shock and swimming failure contribute to drowning deaths in the fishing industry in British Columbia 1976-2002?

Brooks CJ et al. Occup Med (Lond). 2005. PubMed 15871996 · DOI

Who: fishermen who died after immersion in British Columbia, 1976-2002
What: accidental cold-water immersion
Protocol: below 63.5 °F
Measured: underlying cause of immersion death
Result: Reclassified causes: cold shock 5.4%, swimming failure 5.4%, hypothermia 5.4%, post-rescue collapse 0.8%, cardiac event 0.8%, other drowning 10%; cause undeterminable in 72.2%. All deaths occurred in water below 63.5 F (17.5 C) and 95% below 59 F (15 C).
Limitations: accidental occupational immersion; most causes undeterminable

Systematic reviewn = 366Harm

Hypothesised mechanisms of swimming-related death: a systematic review.

Asplund CA et al. Br J Sports Med. 2016. PubMed 26941276 · DOI

Who: 17 studies of mechanisms of swimming-related death (open water and triathlon)
What: swimming, including cold open water
Measured: mechanism of swimming-related death
Result: Limited, inconsistent evidence suggests cardiac arrhythmia is the most likely cause of swimming-related death; evidence does not support pulmonary edema, hypothermia or hyperthermia as frequent causal mechanisms.
Limitations: low-quality, disease-oriented evidence

Pilot / uncontrolled studyMixed

Cold shock response in healthy children: reassessment and first comparison between cold and warm water immersion.

Peter S et al. Front Sports Act Living. 2025. PubMed 41602813 · DOI · Free full text

Who: healthy children
What: neck-deep immersion in 93 F water, then 52 F water
Protocol: 52 (cold); 93 (warm) °F
Measured: cold shock response
Result: In 52 F water heart rate rose 31% and respiratory rate 58%, peaking at 30 s and starting to normalize after 60 s; no change in warm water. The cold shock response was less intense than reported in adults.
Limitations: healthy children; n not stated in abstract

Prospective cohortn = 11Harm

Hypothermia and afterdrop following open water swimming: the Alcatraz/San Francisco Swim Study.

Nuckton TJ et al. Am J Emerg Med. 2000. PubMed 11043627 · DOI

Who: swimmers in an open-water New Year's Day swim without wetsuits
What: open-water swim in 53 F water
Protocol: 53 °F
Measured: rectal temperature for 45 min after exit (afterdrop)
Result: Hypothermia below 96.8 F (36.0 C) in 5 of 11 and below 95.0 F (35.0 C) in 1; afterdrop (continued cooling after leaving the water) in 10 of 11. Higher surface-to-volume ratio and lower BMI predicted lower temperatures.
Limitations: small; single event

Prospective cohortn = 109Harm

Hypothermia is a significant medical risk of mass participation long-distance open water swimming.

Brannigan D et al. Wilderness Environ Med. 2009. PubMed 19364182 · DOI

Who: competitors in an 11.9-mile (19.2 km) open-water race, Western Australia
What: long-distance open-water swim
Measured: hypothermia (below 95 F) and failure to finish
Result: Hypothermia was the most common race-related illness: 26 of 35 swimmers screened, with 5 needing short-stay hospital care and 2 critical care transfer. Longer race duration raised risk (OR 1.77, 95% CI 1.10-2.84); higher BMI lowered it (OR 0.57, 0.41-0.79).
Limitations: only swimmers with symptoms screened; competitive event

Prospective cohortn = 14Harm

Analysis of Factors Associated With Continued Cooling of Core Temperature After Prolonged Cold-Water Swimming.

Drigny J et al. Int J Sports Physiol Perform. 2023. PubMed 36754061 · DOI

Who: swimmers in a qualifying cold-water swim for a channel crossing
What: swim laps for up to 6 h in 54.5-55.4 F water
Protocol: 54.5-55.4 °F
Measured: continued core cooling after exit
Result: Mean core temperature on exit 95.4 F (35.21 C); core cooling continued for a mean 25 min after exit, to a minimum of 94.4 F (34.66 C); higher BMI and fat mass were associated with longer continued cooling.
Limitations: small; prolonged swims, not brief plunges

Systematic reviewn = 174Harm

Swimming induced pulmonary oedema in athletes - a systematic review and best evidence synthesis.

Hohmann E et al. BMC Sports Sci Med Rehabil. 2018. PubMed 30410770 · DOI · Free full text

Who: 29 studies of swimming-induced pulmonary edema in athletes
What: strenuous swimming, mostly in cold water
Measured: prevalence, mechanisms and presentation of SIPE
Result: SIPE presents with cough, dyspnea, frothy sputum and hemoptysis; strong association between cold-water immersion and rises in central venous, pulmonary artery and wedge pressures; moderate association between water temperature and SIPE prevalence.
Limitations: many studies at moderate to critical risk of bias

Case-controln = 2,375Harm

Suggested Novel Risk Factors for Swimming-Induced Pulmonary Edema: Asthma and Limited Open Water Swimming Experience.

Kristiansson L et al. Chest. 2026. PubMed 41903839 · DOI · Free full text

Who: 258 SIPE cases and 2,117 controls from a large Swedish open-water swimming event, 2017-2024
What: open-water swimming
Measured: risk factors for swimming-induced pulmonary edema
Result: Independently associated with SIPE: female sex (OR 5.3, 95% CI 3.6-7.7), age 61 or older (OR 7.3, 3.8-14.2), hypertension (1.9, 1.2-3.2), heart disease (6.0, 2.5-14.2), asthma (1.7, 1.2-2.6), no open-water swimming that season (3.6, 2.4-5.4), prior respiratory symptoms while swimming (3.5) and acute respiratory infection (10.2, 5.2-20.2).
Limitations: case-control; controls recruited by web survey

Pilot / uncontrolled studyn = 54Mixed

Assessment of arrhythmias and heart rate response in healthy adolescents performing face immersion and body submersion in ice-cold water.

Lundström A et al. Physiol Rep. 2025. PubMed 40624837 · DOI · Free full text

Who: healthy adolescents aged 15-16
What: face immersion in 50 F water (n=54) and body immersion in 36 F water (n=20)
Protocol: 50 (face); 36 (body) °F
Measured: arrhythmias and heart rate response
Result: Face immersion: supraventricular extrasystoles in 6 and ventricular bigeminy in 2 of 54. Body immersion: supraventricular extrasystoles in 4 of 20. Authors judge the risk of severe arrhythmia from brief body immersion low but potentially higher with face submersion and breath-holding.
Limitations: healthy adolescents; brief exposures

Prospective cohortn = 20Harm

Cardiac electrical and functional activity following an outdoor cold-water swimming event.

Faivre-Rampant V et al. J Therm Biol. 2024. PubMed 39461093 · DOI · Free full text

Who: trained adults (mean age 47) in an outdoor cold-water swimming event
What: swim laps for up to 6 h in 59 F water
Protocol: 59 °F
Measured: ECG and echocardiography before and after
Result: QTc lengthened from 437.7 to 457.2 ms (p=0.012), with 5 participants above 500 ms after the swim; biventricular systolic function and left ventricular relaxation unchanged; minimum core temperature 96.1 F (35.6 C).
Limitations: small; prolonged exercise plus cold; healthy trained adults

Case series / reportn = 9Harm

Transient Global Amnesia Triggered by Cold Water Swimming: A Series of 9 Cases Presenting to a Hospital on the Coast of Ireland Within 5 Years.

Tuohy C et al. Eur J Case Rep Intern Med. 2025. PubMed 40270669 · DOI · Free full text

Who: women aged 55-82 presenting to an Irish coastal hospital, 2019-2024
What: sea swimming in 48.6-64.4 F water
Protocol: 48.6-64.4 °F
Measured: transient global amnesia
Result: All 9 had transient global amnesia during or right after sea swimming, lasting 1-7 hours; neuroimaging showed no acute change; all resolved within 24 hours.
Limitations: single-hospital case series; no denominator

Case series / reportn = 1Harm

Amnesia during cold water immersion: a case report.

Castellani JW et al. Wilderness Environ Med. 1998. PubMed 11990187 · DOI

Who: young volunteer in a cold-water research protocol
What: three 120-min immersions in 68 F water in one day
Protocol: 68 °F · 120 min
Measured: transient global amnesia
Result: 20 min of transient global amnesia during the third immersion at a rectal temperature of 96.1 F (35.6 C).
Limitations: single case

Case series / reportn = 21Harm

Cold Anaphylaxis in Children: Italian Case Series and Review of the Literature.

Tomei L et al. Diseases. 2023. PubMed 37873787 · DOI · Free full text

Who: children with a history of cold-induced anaphylaxis (Italian series plus literature review)
What: cold exposure, including cold-water immersion
Measured: cold anaphylaxis
Result: Cold urticaria is the only inducible urticaria with anaphylaxis risk without cofactors; authors advise an adrenaline auto-injector for high-risk patients, including those whose urticaria is triggered by cold-water immersion.
Limitations: case series with narrative review

Systematic reviewn = 28Harm

Contraindications to Whole-Body Cryostimulation (WBC). A position paper from the WBC Working Group of the International Institute of Refrigeration and the multidisciplinary expert panel.

Capodaglio P et al. Front Rehabil Sci. 2025. PubMed 40303546 · DOI · Free full text

Who: Delphi panel of 28 European experts after a systematic literature search
What: whole-body cryostimulation (cryochamber)
Measured: consensus list of contraindications
Result: Consensus reached on a final list of temporary and absolute contraindications to whole-body cryostimulation after two Delphi rounds (56 items retained of 59); the abstract does not list the items.
Limitations: expert consensus; items in full text only

Systematic reviewMixed

Evaluating safety risks of whole-body cryotherapy/cryostimulation (WBC): a scoping review from an international consortium.

Legrand FD et al. Eur J Med Res. 2023. PubMed 37770960 · DOI · Free full text

Who: 5 case reports and 2 RCTs reporting adverse events of whole-body cryotherapy
What: whole-body cryotherapy chamber
Measured: documented adverse events
Result: 16 documented adverse events; authors judge risks acceptable when existing contraindications and guidelines are followed, and note that some reported harms came from partial-body (liquid nitrogen tub) devices rather than true whole-body chambers.
Limitations: scoping review of sparse reports; authors from the cryotherapy research field

Cross-sectional studyn = 29Harm

Retrospective analysis of whole-body cryotherapy adverse effects in Division I collegiate athletes.

Kelly EA et al. J Osteopath Med. 2023. PubMed 36927611 · DOI · Free full text

Who: Division I collegiate athletes who had used whole-body cryotherapy
What: whole-body cryotherapy
Measured: self-reported adverse effects
Result: Within 1 h: skin rash 27.6%, itching 13.8%, fatigue 6.9%; 58.6% reported no adverse effect. Burns and itching were the main negative effects.
Limitations: 6.3% response; retrospective survey

Case series / reportn = 3Harm

Cryotherapy Induced Burns: A Case Series of Three Patients.

Ellis RC et al. J Burn Care Res. 2022. PubMed 35245366 · DOI

Who: three men aged 17-28
What: single whole-body cryotherapy session below -148 F (-100 C)
Protocol: below -148 °F
Measured: frostbite (cold burn)
Result: One full-thickness frostbite needing excision and grafting; two partial-thickness injuries.
Limitations: three cases

Case series / reportn = 1Harm

Cold panniculitis: Adverse cutaneous effect of whole-body cryotherapy.

Greenwald E et al. JAAD Case Rep. 2018. PubMed 29693065 · DOI · Free full text

Who: person treated with whole-body cryotherapy
What: whole-body cryotherapy
Measured: cold panniculitis
Result: Abstract not available; listed for completeness. The title reports cold panniculitis as an adverse cutaneous effect of whole-body cryotherapy.
Limitations: no abstract; single case

Case series / reportn = 1Harm

Abdominal Aortic Dissection and Cold-Intolerance After Whole-Body Cryotherapy: A Case Report.

Cámara-Lemarroy CR et al. Clin J Sport Med. 2017. PubMed 28829347 · DOI

Who: 56-year-old patient
What: 15 whole-body cryotherapy sessions
Measured: abdominal aortic dissection
Result: Abdominal aortic dissection after 15 sessions without other strong risk factors; authors propose cold-induced rises in blood pressure and heart rate as a trigger.
Limitations: single case; causality uncertain

Case series / reportn = 1Harm

Transient global amnesia following a whole-body cryotherapy session.

Carrard J et al. BMJ Case Rep. 2017. PubMed 29030365 · DOI · Free full text

Who: 63-year-old man
What: whole-body cryotherapy session
Measured: transient global amnesia
Result: Transient global amnesia after a session, with complete recovery within 24 hours.
Limitations: single case

Case series / reportn = 1Harm

Reversible Cerebral Vasoconstriction Syndrome Triggered by Whole-Body Cryotherapy in a Teenager.

Dantas M et al. J Child Neurol. 2026. PubMed 41452070 · DOI

Who: adolescent
What: whole-body cryotherapy session
Measured: reversible cerebral vasoconstriction syndrome
Result: Reversible cerebral vasoconstriction syndrome diagnosed after a session preceding the symptoms.
Limitations: single case; temporal association only

Never alone, never after alcohol.

Both therapies cause sudden shifts in blood pressure and heart rate. Use them sober, hydrated, and with someone nearby, especially when you are starting out or have a heart condition.