Blood pressure in a sauna

Blood pressure in a sauna changes acutely during bathing and again during the cooling phase. The pattern in a healthy bather is characteristic — a moderate rise of systolic pressure early in the session, followed by a gradual fall, and often a dip below the resting value after leaving the hot room — and it is one of the best-documented cardiovascular responses to Finnish sauna bathing. Its clinical interpretation depends on why a person is measuring, and on their underlying blood pressure status.

The acute response

The immediate driver of the pressure change is the circulatory response described under Heart rate in a sauna and Cardiovascular effects of sauna: the skin vessels dilate to carry heat to the surface, cardiac output rises, and the systolic pressure is temporarily supported by the increased stroke volume. In a typical session at 80–90 °C, systolic pressure in a normotensive person rises by some 10–25 mmHg in the first minutes and then tends to fall as vasodilation progresses and blood is redistributed to the skin; diastolic pressure changes less consistently and may fall. The values return toward, and often slightly below, the resting level after the session, an after-effect linked to persisting vasodilation and to the resetting of vascular tone during recovery.

The response exaggerates whatever pattern the bather already has. In someone with raised resting pressure, the same session can produce larger swings; in someone with low resting pressure, the early rise is smaller and the subsequent fall more pronounced. The largest and least predictable change is the orthostatic reaction: after a hot session, when a bather stands up suddenly, vasodilation and the pooling of blood in the legs can briefly lower the pressure reaching the head, producing dizziness or, in the pronounced case, a faint (see Fainting in a sauna). Standing up slowly and sitting for a moment before leaving the room are the standard prevention.

Comparisons of the acute pattern with exercise show that the blood pressure and heart-rate curve during bathing corresponds to that of submaximal dynamic exercise of mild to moderate intensity rather than to a resting state, and the physiological literature treats the Finnish sauna as a form of passive cardiac stress.

Measurement in the sauna

Measuring blood pressure during bathing is useful only under defined conditions, because both the measurement and the measured quantity are labile. Automated arm-cuff devices can misread in the heat: the skin is warm and vasodilated, the cuff may not seat properly over sweaty skin, and the value drifts quickly with posture and time. Auscultatory measurement by another person is more reliable but shares the problem that the pressure genuinely changes over minutes. Readings intended for clinical use should be taken after a period of quiet rest, away from the heat of the immediately preceding session, and compared with values obtained in the same posture (see Blood pressure measurement in a sauna and Core temperature measurement in a sauna for related practical guidance).

For continuous recording in research, finger or wrist transducers and beat-to-beat devices are used alongside heart rate monitoring, and the combined curves are part of the standard picture of Blood circulation in bathing. Infrared or exercise-style upper-arm monitors sold for home use are not validated for very warm, humid environments, and their values should be treated cautiously.

Long-term associations

Beyond the acute pattern, epidemiological work from Finland has examined whether the frequency of sauna bathing is associated with the later development of hypertension. In a prospective cohort of middle-aged Finnish men, four or more sauna sessions per week were associated with a lower incidence of hypertension compared with one session or fewer, after adjustment for a range of lifestyle and health factors. The study is observational: it does not establish that bathing prevents high blood pressure, and the direction could involve healthier lifestyles among frequent bathers. The authors of the sauna literature generally present the association as consistent with the acute cardiovascular effects of repeated heat exposure, but as unproven in the sense of controlled intervention. Similar reservations apply to the association between frequent bathing and lower cardiovascular mortality reported in the same Finnish cohorts (see Sauna epidemiology and Clinical sauna studies). No study supports the use of the sauna as a treatment for existing hypertension; the management of the condition follows ordinary medical advice (see Medical advice before sauna).

Practical implications

For the ordinary bather, the message is that blood pressure in the heat is expected to vary, and that the variation is usually harmless if two rules are kept. First, transitions should be gentle: sitting up slowly, letting the circulation adjust, and never jumping from a hot bench into cold water immediately after standing. Second, bathers feeling unwell — dizzy, nauseated, or with a racing or irregular pulse — should cool down promptly rather than wait for the pressure to "settle" (see Overheating prevention). People with treated hypertension, on pressure-lowering medication, or with heart failure or rhythm disorders are more sensitive both to the falls and to the transient rises, and should follow the advice in Medication and sauna and Sauna contraindications. Sauna research and Sauna and health summarise what is known about the longer-term cardiovascular picture.

See also

• High blood pressure and sauna
• Low blood pressure and sauna
• Fainting in a sauna
• Cardiovascular effects of sauna
• Blood pressure measurement in a sauna

References

• Zaccardi F, Laukkanen T, Willeit P, Kunutsor SK, Kauhanen J, Laukkanen JA. "Sauna bathing and incident hypertension: a prospective cohort study." American Journal of Hypertension 30:1120–1125, 2017. doi:10.1093/ajh/hpx102
• Kukkonen-Harjula K, Kauppinen K. "Health effects and risks of sauna bathing." International Journal of Circumpolar Health 65(3):195–205, 2006. doi:10.3402/ijch.v65i3.18102
• Ketelhut S, Ketelhut RG. "The blood pressure and heart rate during sauna bath correspond to cardiac responses during submaximal dynamic exercise." Complementary Therapies in Medicine 44:218–222, 2019. doi:10.1016/j.ctim.2019.05.002
• Heinonen I, Laukkanen JA. "Effects of heat and cold on health, with special reference to Finnish sauna bathing." American Journal of Physiology – Regulatory, Integrative and Comparative Physiology 314(5):R629–R638, 2018. doi:10.1152/ajpregu.00115.2017
• Laukkanen JA, Laukkanen T, Kunutsor SK. "Cardiovascular and other health benefits of sauna bathing: a review of the evidence." Mayo Clinic Proceedings 93(8):1111–1121, 2018. doi:10.1016/j.mayocp.2018.04.008
• Laukkanen T, Khan H, Zaccardi F, Laukkanen JA. "Association between sauna bathing and fatal cardiovascular and all-cause mortality events." JAMA Internal Medicine 175(4):542–548, 2015. doi:10.1001/jamainternmed.2014.8187
• Hussain J, Cohen M. "Clinical effects of regular dry sauna bathing: a systematic review." Evidence-Based Complementary and Alternative Medicine 2018:1857413, 2018. doi:10.1155/2018/1857413