Clinical Effects of Regular Dry Sauna Bathing: A Systematic Review

Abstract

Abstract
Introduction
Sauna bathing has a long tradition in many cultures. Many health benefits are claimed by individuals and facilities promoting sauna bathing, however the medical evidence to support these claims is not well established. This paper aims to systematically review recent research on the effects of repeated dry sauna interventions on human health.
Methods
A systematic search was made of medical databases for studies reporting on the health effects of regular dry sauna bathing on humans from 2000 onwards. Risk of bias was assessed according to the Cochrane Collaboration guidelines.
Results
Forty clinical studies involving a total of 3855 participants met the inclusion criteria. Only 13 studies were randomized controlled trials and most studies were small (n<40) and investigated a wide variety of healthy and diseased populations although more than half of the studies involved populations with elevated cardiovascular risk. Reported outcome measures were heterogeneous with most studies reporting beneficial health effects. Only one small study (n=10) reported an adverse health outcome of disrupted male spermatogenesis, with all effects being reversed within 6 months of ceasing sauna activity.
Conclusions
Regular dry sauna bathing has potential health benefits and may be particularly beneficial for people with cardiovascular-related conditions. Regular sauna bathing is associated with psychological, physiological, and metabolic effects fitting a hormetic stress model similar to exercise that may be contributing to its clinical benefits. Although dry sauna bathing appears to be well tolerated in clinical settings, more data of higher quality is needed on the frequency and extent of adverse side effects. Further study is also needed to determine the optimal frequency and duration of distinct types of sauna bathing for targeted health effects and the specific clinical populations who are most likely to benefit.

Full text

Review Article
Clinical Effects of Regular Dry Sauna Bathing:
A Systematic Review
Joy Hussain and Marc Cohen
School of Health and Biomedical Sciences, RMIT University, Melbourne, VIC, Australia
Correspondence should be addressed to Joy Hussain; joyhussain@gmail.com
Received 9 October 2017; Revised 14 December 2017; Accepted 8 January 2018; Published 24 April 2018
Academic Editor: Kieran Cooley
Copyright ©  Joy Hussain and Marc Cohen. is is an open access article distributed under the Creative Commons Attribution
License, which permits unrestricted use, distribution, and reproduction in any medium,provided the original work is properly cited.
Introduction. Many health benets are claimed by individuals and facilities promoting sauna bathing; however the medical evidence
to support these claims is not well established. is paper aims to systematically review recent research on the eects of repeated
dry sauna interventions on human health. Methods. A systematic search was made of medical databases for studies reporting on
the health eects of regular dry sauna bathing on humans from  onwards. Risk of bias was assessed according to the Cochrane
Collaboration guidelines. Results. Forty clinical studies involving a total of  participants met the inclusion criteria. Only 
studies were randomized controlled trials and most studies were small (𝑛 < 40). Reported outcome measures were heterogeneous
with most studies reporting benecial health eects. Only one small study (𝑛 = 10)reporte d an adverse health outcome of disr upted
male spermatogenesis, demonstrated to be reversible when ceasing sauna activity. Conclusions. Regular dry sauna bathing has
potential health benets. More data of higher quality is needed on the frequency and extent of adverse side eects. Further study is
also needed to determine the optimal frequency and duration of distinct types of sauna bathing for targeted health eects and the
specic clinical populations who are most likely to benet.
1. Introduction
Sauna bathing is a form of whole-body thermotherapy that
has been used in various forms (radiant heat, sweat lodges,
etc.) for thousands of years in many parts of the world
for hygiene, health, social, and spiritual purposes. Modern
day sauna use includes traditional Finnish-style sauna, along
with Turkish-style Hammam, Russian Banya, and other
cultural variations, which can be distinguished by the style
of construction, source of heating, and level of humidity.
Traditional Finnish saunas are the most studied to date
and generally involve short exposures (− minutes) at
temperatures of ∘C–∘Cwithdryair(relativehumidityof
% to %) interspersed with periods of increased humidity
created by the throwing of water over heated rocks []. In the
past decade, infrared sauna cabins have become increasingly
popular. ese saunas use infrared emitters at dierent wave-
lengths without water or additional humidity and generally
run at lower temperatures (–∘C) than Finnish saunas
with similar exposure times []. Both traditional Finnish
and infrared sauna bathing can involve rituals of cooling-of
f periods and rehydration with oral uids before, during,
and/or aer sauna bathing.
Sauna bathing is inexpensive and widely accessible with
Finnish-style saunas more oen used in family, group, and
public settings and infrared saunas more commonly built and
marketed for individual use. Public sauna facilities can be
located within exercise facilities and the relationship between
saunas and exercise, which may include synergistic hormetic
responses, is an area of active research [–]. e use of
private saunas, especially involving infrared saunas, is also
increasing and saunas are used for physical therapy in mas-
sage clinics, health spas, beauty salons, and domestic homes.
is trend is capitalising on the call for additional lifestyle
interventions to enhance health and wellness particularly
in populations that have diculty exercising (e.g., obesity,
chronic heart failure, chronic renal failure, and chronic
liver disease) []. Facilities oering sauna bathing oen
Hindawi
Evidence-Based Complementary and Alternative Medicine
Volume 2018, Article ID 1857413, 30 pages
https://doi.org/10.1155/2018/1857413

 Evidence-Based Complementary and Alternative Medicine
claim health benets that include detoxication, increased
metabolism, weight loss, increased blood circulation, pain
reduction, antiaging, skin rejuvenation, improved cardiovas-
cular function, improved immune function, improved sleep,
stress management, and relaxation. However, rigorous medi-
cal evidence to support these claims is scant and incomplete,
as emphasized in a recent multidisciplinary review of sauna
studies [].
ere is considerable evidence to suggest that sauna
bathing can induce profound physiological eects [, –].
Intense short-term heat exposure elevates skin temperature
andcorebodytemperatureandactivatesthermoregula-
tory pathways via the hypothalamus [] and CNS (central
nervous system) leading to activation of the autonomic
nervous system. e activation of the sympathetic ner-
vous system, hypothalamus-pituitary-adrenal hormonal axis,
and the renin-angiotensin-aldosterone system leads to well-
documented cardiovascular eects with increased heart rate,
skin blood ow, cardiac output, and sweating [, ]. e
resultant sweat evaporates from the skin surface and produces
cooling that facilitates temperature homeostasis. In essence,
sauna therapy capitalises on the thermoregulatory trait of
homeothermy, the physiological capability of mammals and
birds to maintain a relatively constant core body temperature
with minimal deviation from a set point []. It is currently
unclear whether steam saunas invoke the same degree of
physiological responses as dry saunas [], as the higher
humidity results in water condensation on the skin and
reduced evaporation of sweat [].
On a cellular level, acute whole-body thermotherapy
(both wet and dry forms) induces discrete metabolic changes
that include production of heat shock proteins, reduction
of reactive oxygenated species, reduced oxidative stress and
inammation pathway activities, increased NO (nitric oxide)
bioavailability, increased insulin sensitivity, and alterations
in various endothelial-dependent vasodilatation metabolic
pathways []. It has been suggested that heat stress induces
adaptive hormesis mechanisms similar to exercise, and there
are reports of cellular eects induced by whole-body hyper-
thermia in conjunction with oncology-related interventions
(i.e., chemotherapy and radiotherapy) []; however the
mechanisms by which the physiological and cellular changes
induced by sauna bathing contribute to enhanced health
and/or therapeutic eects is still being explored [, , , –
].
e following systematic review was undertaken to
explore recent research on the clinical eects of repeated dry
sauna bathing (Finnish-style, infrared, or other dry sauna
forms) to document the full range of medical conditions
saunas have been used for, as well as any associated health
benets and/or adverse eects observed. While a small
number of reviews of sauna bathing and health have been
conductedinthepast[,,–],asfarasweknow,thisis
the rst systematic review of sauna and health to include both
Finnish and infrared saunas. Furthermore, this review only
considers eects related to regular, multiple sessions of sauna
activity rather than single sauna sessions, to better reect the
use of sauna bathing as a regular lifestyle intervention.
2. Methods
PRISMA guidelines for conducting systematic reviews were
followed, including the use of validated tools to assess the risk
of bias in randomized controlled trials [–].
2.1. Eligibility Criteria. Studies of humans undergoing
repeated dry sauna bathing that reported on health measures
were included in the review. Studies were included for initial
review if they were published in English language from
January  onwards and involved research in humans
undergoing repeated dry sauna sessions with at least one
reported health outcome. Studies involving predominantly
high-humidity (>%) wet/steam “sauna” or immersion
hydrotherapy were excluded for the potential confounding
mechanisms of dierential sweating rates and explicit focus
of this review limited to “dry sauna” interventions. Studies
of partial body heating were excluded since proposed
mechanisms of action may or may not be the same as whole-
body heating. Studies reporting primarily animal-based,
nonhuman ndings were excluded given the recognized
dierences in end-organ (skin) structure and responses
(sweating mechanisms) between animals and humans.
Studies of “sauna” as a recruitment venue for potential sexual
activity, primarily regarding men who have sex with men
(MSM), were excluded since these studies lacked details
of sauna interventions, confounding whether wet or dry
interventions, and measured health metrics focused to sexual
activity but not necessarily to sauna activity.
2.2. Search Strategy. PubMed, Web of Science, Scopus, and
Proquest were initially searched with key word “sauna” and
date restrictions of January –April . Search dates
were chosen to focus on updated ndings reecting advanc-
ing technology in both diagnostics and physiological mon-
itoring to build upon the foundational literature of prior
nonsystematic clinical reviews of sauna activity published in
the early s. Aer further restrictions of English language
and humans, records were then expanded using Google
Scholar, with searches for other research by key authors,
searches of citations and reference lists of original and review
articles, and other “related articles”. Additional searches with
expanded keywords relating to sauna including “interven-
tional study”, “whole body hyperthermia”, and “whole body
thermotherapy” were also conducted with the same initial
restrictions.
2.3. Data Extraction. Abstracts of initially identied studies
were screened by investigator JH and then the complete
full-text articles of potentially eligible studies were carefully
screened by both investigators JH and MC for research
design, population descriptive data, timing and physical
details of dry sauna intervention, outcome measures, key
results, and adverse eects. Discrepancies regarding inclusion
of studies or data extraction were discussed until consensus
was reached.
2.4. Assessment for Risk of Bias. Included randomized con-
trolledtrials(RCTs)wereassessedforriskofbiasaccordingto

Evidence-Based Complementary and Alternative Medicine 
Jan 2000–April 2017
PubMed
484 citation(s)
Jan 2000–April 2017
843 citation(s)
Web of Science
Jan 2000–April 2017
803 citation(s)
Scopus
Jan 2000–April 2017
1155 citation(s)
Proquest-Health and Medicine
906 nonduplicate
citations screened
Inclusion-English language and human
Exclusion-gay (MSM) focus, steam/wet sauna, hydrotherapy,
partial body heating, animal-based studies, sauna-personal name
738 articles excluded
aer title/abstract screen
168 articles retrieved
Same inclusion/exclusion
criteria applied to full text
40 articles included
99 articles excluded
aer full-text screen
29 articles excluded
during data extraction
F : PRISMA ow diagram of evidence searches and inclusions/exclusions.
theCochraneCollaboration’stoolforassessingbiasandcal-
culated Jadad et al. scores []. Domains of bias assessed were
selection bias (by looking for random sequence generation
and allocation concealment), performance bias (by published
mention of blinding of participants and personnel), detection
bias (by documented attempts to blind outcome assessment),
attrition bias (by evaluating for incomplete outcome data),
reporting bias (by any indication of selective reporting of
outcomes), and other bias (e.g., conclusions not clearly
supportedbyreportedoutcomes).Riskofbiaswasinitially
assessed by investigator JH as “low”, “unclear”, or “high” and
then conrmed by investigator MC. Any discrepancies were
discussed until consensus was reached.
3. Results
3.1. Literature Search. Figure  summarises the screening and
assessment strategies used with the search results. Of the 
nonduplicate citations initially identied,  were excluded
aer a review of the abstracts.
Aer retrieving  full-text articles and applying the
same exclusion criteria as discussed above along with exclud-
ing review articles, case reports, and letters to the editor, 
independent human studies involving dry sauna interven-
tions were identied for further analysis.
In the data extraction step, one study was excluded since
it was essentially a case series with two patients, mistakenly
identied as an interventional trial conducted by a key
author []. Another  studies were excluded due to the
intervention being only a single session of sauna and not
repeated sauna therapy, which is the stated focus of this
review.
A total of  studies remained for inclusion in this
systematic review. A summary of extracted data is presented
in Tables –, with tables categorised according to participant
population.
3.2. Study Design. Of the forty studies,  were randomized
controlled trials (RCTs),  were trials with nonrandomized
control groups and  were prospective cohort studies. e
remainder of studies were single-group or multigroup inter-
ventional trials (without a control group) or retrospective
studies. e following three levels of evidence were used to
help stratify the quality of the studies.
Levels of Evidence
Level I: multicentre or single-centre, randomized
controlled trial (RCT)
Level II: controlled interventional trial; prospective
cohort study
Level III: retrospective comparative study; case-
control study; pilot study.
3.3. Limitations/Risk of Bias. Many studies were relatively
small, with limited number of participants, and a limited
number of randomized studies were available for review. Of
the  randomized controlled trials (RCTs) identied, only 
of these studies (involving / participants) [, , ]
were assessed with having a low overall risk of bias according

 Evidence-Based Complementary and Alternative Medicine
T : Cardiovascular disease- (CVD-) related sauna studies.
Study Characteristics Study sample Intervention Comparators Health eects Adverse side
eects
Author &
year
Level of
evidence Design Pop/country 𝑁Sauna
type Duration Comparator/
controls
Outcome
measures Positive/negative/negligible
None/mild/
moderate/
severe

Tei et al. [] IRCT-
multicentre Advanced CHF/Japan  FIR  weeks
Control group,
standard
medical care
MWD
( min walking distance),
CTR (cardio-thoracic ratio)
on chest X-ray, NYHA
class, plasma BNP levels
Positive,
improved  MWD
(𝑝 < 0.05), reduced CTR
on CXR (𝑝 < 0.05),
improved NYHA
classication (𝑝 < 0.05)
compared to control group
Mild,
decreased BP,
hypovolemia,
polyurination,
decreased body
wt

Fujita et al.
[]
I RCT CHF/Japan  FIR  weeks
Control group,
standard
medical care
Body weight, BP,
cardio-thoracic ratio (CTR)
on chest X-ray, LVEF on
ECHO, fasting plasma
levels of BNP, uric acid,
hydro-peroxide, nitrate,
nitrite
Positive,
sauna group with reduced
concentration of
hydroperoxide (𝑝 < 0.001);
reduced BNP levels
(𝑝 < 0.001);
increased nitric oxide
metabolites (𝑝 < 0.05)
None

Kuwahata et
al. []
I RCT CHF/Japan  FIR  weeks
Control group,
standard
medical care
Body weight, BP, HR, CTR
on chest X-ray, standard
ECHO parameters, fasting
plasma levels of
catechol-amines and BNP;
and HRV (heart rate
variability) parameters
Positive,
mean HR decreased
(𝑝 < 0.05)insaunagroup
compared to control group.
High frequency component
of HRV in setting of beta
blockade improved
None

Shinsato et
al. []
IRCT PAD/JapanFIRweeks
Control group,
standard
medical care
Leg pain (using VAS), ABI
(ankle-brachial index),
 MWD (-min walking
distance), PCR-CD+
progenitor gene expression
levels in peripheral blood
mononuclear cells, serum
levels of VEGF (vascular
endothelial growth factor),
nitrate, nitrite
Positive,decreaseinleg
pain scores (𝑝<0.05),
increase in  MWD
(𝑝 < 0.01), improved ABI
(𝑝 < 0.01),
-fold increase in mRNA
CD/GAPDH gene
expression levels
(𝑝 = 0.015),
increases in serum nitrate
and nitrite levels (𝑝 < 0.05,
𝑝 < 0.05)insaunagroup
compared to control group
Mild,
transient leg
pain during
sauna but
resolved aer a
few sessions

Evidence-Based Complementary and Alternative Medicine 
T   : C ont i nued.
Study Characteristics Study sample Intervention Comparators Health eects Adverse side
eects
Author &
year
Level of
evidence Design Pop/country 𝑁Sauna
type Duration Comparator/
controls
Outcome
measures Positive/negative/negligible
None/mild/
moderate/
severe

Miyata et al.
[]
IRCT CHF/Japan  FIR  weeks
Control group-
standard
medical care
BP, HR, body weight, body
temp, CTR (cardio-thoracic
ratio) on chest X-ray, usual
ECHO parameters, fasting
plasma BNP
Positive,
BP and CTR decreased in
both groups (sauna
𝑝 < 0.01,𝑝 < 0.001;
control 𝑝 < 0.05,𝑝<0.05).
Body wt decreased
(𝑝 < 0.0001); LVEF on
ECHO increased
(𝑝 < 0.0001); plasma BNP
decreased (𝑝 < 0.001)in
sauna group compared with
control group
None

Kihara et al.
[]
IRCT Cardiac arrhythmias,
CHF/Japan  FIR  weeks
Control group
placebo
intervention
-supine on a bed
in a
temp-controlled
room at ∘Cfor
 min.
Self-assessed quality of life
questionnaire,
-hr ambulatory ECG
recordings with HRV
analysis (std deviation of
mean RR intervals), CTR
(cardiothoracic ratio) by
chest X-ray, usual ECHO
parameters, plasma
concentrations of
catechol-amines, ANP, BNP
Positive,
fewer PVCs (𝑝 < 0.01),
fewer couplets (𝑝 < 0.05),
fewer episodes of VT
(𝑝 < 0.01), decreased CTR
(𝑝 < 0.05), increased HRV
variability (𝑝 < 0.01),
lowered serum levels of
BNP (𝑝 < 0.01)insauna
treatment group compared
to control group
None

Masuda et
al. []
IRCT Increased CVD
Risk/Japan  FIR  weeks
Control group
placebo
intervention
-supine on a bed
in a
temp-controlled
room at ∘Cfor
 min.
Body wt, HR, BP, HCT,
fasting plasma lipid prole
and glucose, urinary levels
-epi-prosta-glandin F2𝛼
Positive,
systolic BP (𝑝<0.05)and
urinary -epi-
prostaglandin F2𝛼 levels
(𝑝 < 0.001) signicantly
lower in sauna group
compared to control group
None

Laukkanen
et al. []
II Prospective
cohort study
Middle-aged
males/Finland  Finnish . years
Frequency and
duration of
sauna bathing:
 time/wk,
- time/wk,
– times/wk
Incidence
dementia/Alzheimer’s
disease and other
CVD-related outcomes
Positive,
sauna bathing − times a
week associated with %
risk reduction (hazard ratio
., % CI) in developing
dementia or Alzheimer’s
compared with  time/week
None

 Evidence-Based Complementary and Alternative Medicine
T   : C ont i nued.
Study Characteristics Study sample Intervention Comparators Health eects Adverse side
eects
Author &
year
Level of
evidence Design Pop/country 𝑁Sauna
type Duration Comparator/
controls
Outcome
measures Positive/negative/negligible
None/mild/
moderate/
severe

Laukkanen
et al. []
II Prospective
cohort study
Middle-aged
males/Finland  Finnish . years
Frequency and
duration of
sauna bathing:
 time/wk,
- time/wk,
– times/wk
Incidence of sudden
cardiac death,
fatal coronary heart disease,
fatal CVD, all-cause
mortality
Positive,
sauna bathing – sessions
weekly associated with %
reductioninall-cause
mortality compared with 
session weekly, (hazard
ratio ., % CI,
.–., 𝑝 < 0.001)
None

Sobajima et
al. []
II Controlled
clinical study
IHD with total coronary
occlusion/Japan  FIR  weeks
Control group,
standard
medical care
Myocardial perfusion
scintigraphy with
adenosine, ow-mediated
vaso-dilation of brachial
artery, treadmill exercise
stress testing and
expression of
CD-positive bone
marrow-derived cells
Positive,
improved indices of defect
reversibility on myocardial
perfusion scans (𝑝 < 0.01);
extended treadmill times
(𝑝 < 0.01), improved
ow-mediated dilation of
brachial artery (𝑝 < 0.05)
aer sauna therapy
compared to control group
None

Sugahara et
al. []
II Single group
clinical study
Infants-
VSD and CHF/Japan  FIR  weeks No control
group
Core body temp, HR, BP,
usual ECHO parameters
including VSD
measurements with colour
Doppler,  h urine nitrate
and nitrite levels
Positive,
decrease in VSD shunt ow
ratio (𝑝 < 0.05), increase in
 h urine nitrite and urine
nitrate levels (𝑝<0.05,
𝑝 < 0.05); surgical repair
not necessary for /
(%) infants
None

Ohori et al.
[]
III Single group
clinical study CHF/Japan  FIR  weeks No control
group
 MWT (-min walk test);
standard ECHO
parameters;
plasma levels of BNP,
norepinephrine and
circulating CD+ cells;
ow-mediated dilation
(FMD) of the brachial
artery
Positive,
increased LVEF (le
ventricular ejection
fraction), 𝑝 = 0.023;
reduced levels of
norepinephrine and BNP,
𝑝 = 0.015 and 𝑝 = 0.035;
increased  MW T,
𝑝 < 0.001;improvedFMD,
𝑝 < 0.001;increased
CD+ counts, 𝑝 = 0.025
None

Evidence-Based Complementary and Alternative Medicine 
T   : C ont i nued.
Study Characteristics Study sample Intervention Comparators Health eects Adverse side
eects
Author &
year
Level of
evidence Design Pop/country 𝑁Sauna
type Duration Comparator/
controls
Outcome
measures Positive/negative/negligible
None/mild/
moderate/
severe

Beever [] III
Single group,
sequential,
longitudinal,
interrupted
time series
Type  diabetes/Canada  FIR  months No control
group
SF- (-item short form
health survey) and VAS
(visual analogue scales)
Positive,
improved stress
(𝑝 = 0.042), fatigue
(𝑝 = 0.014), general health
(𝑝 = 0.037)onSF-
None

Kihara et al.
[]
III Retrospective
cohort study CHF/Japan  FIR  years
Control group,
standard
medical care
Episodes of cardiac death,
cardiac events,
rehospitalisations due to
CHF
Positive,
/ patients died in sauna
therapy group vs /
patients in control group
(.% vs .% mortality
rate);
Rehospitalization due to
worsening CHF occurred
in / (.%) patients in
sauna group vs /
(.%) patients in control
group (𝑝 < 0.01); %
reduction in cardiac event
rate in sauna therapy group
compared to control group
None

Tei et a l .
[]
III
Single group
clinical
study/pilot
trial
PAD/ Jap an  F I R  w eeks No control
group
Leg pain using VAS (visual
analogue scale),  MWD
( min walking distance),
ABI (ankle/
brachial index), leg blood
ow with Doppler laser
imaging, digital subtraction
angiography
Positive,
pain scores decreased,
MWDimproved, ABI
improved, increase in
visible collateral vessels in
ischaemic legs with digital
subtraction angiography
observed aer sauna
therapy (𝑝 < 0.01 for all)
None

Miyamoto
et al. []
III
Single group
clinical
study/pilot
trial
CHF/Japan  FIR  weeks No control
group
Body wt, BP, HR;
Self-assessed quality of life
questionnaire;  MWT
( min walk time); peak
VO2on bicycle ergometer;
CTR (cardio-thoracic ratio)
on chest X-ray; usual
ECHO parameters, plasma
BNP, catecholamines;
number of hospitalisations
one-year aer sauna
intervention
Positive,
decreased SBP (𝑝 < 0.05),
improved CTR (𝑝 < 0.05),
improved LVEF on ECHO
(𝑝 < 0.05), increased
MWT(𝑝 < 0.05),
decreased plasma
norepinephrine and
epinephrine levels
(𝑝 < 0.01,𝑝 < 0.05)with
sauna intervention.
Reduced number of
hospitalisations (𝑝 < 0.01)
one-year aer sauna
intervention
None

 Evidence-Based Complementary and Alternative Medicine
T   : C ont i nued.
Study Characteristics Study sample Intervention Comparators Health eects Adverse side
eects
Author &
year
Level of
evidence Design Pop/country 𝑁Sauna
type Duration Comparator/
controls
Outcome
measures Positive/negative/negligible
None/mild/
moderate/
severe

Biro et al.
[]
III
Clinical study
with control
group
Obesity,
TDM, smoking,
hypercholesterolaemia,
HTN/Japan
 FIR  weeks
/ control
group without
any lifestyle
diseases
Bodywt,HR,BP,HCT;
fasting serum lipid prole,
glucose, uric acid levels;
resting arterial diameter;
ow mediated dilatation of
brachial artery on Doppler
USS; plasma ghrelin and
serumleptinlevels
Positive,
decreased body wt
(𝑝 < 0.05), SBP and DBP
(𝑝 < 0.01,𝑝 < 0.05), FBG
(𝑝 < 0.05);
Improved ow mediated
dilation of brachial artery
(𝑝 < 0.001)insaunagroup
but results compared to
control not presented
None

Kihara et al.
[]
III
Clinical study
with control
group
CHF/Japan  FIR  weeks
/ control
group, standard
medical care
Self-assessed
quality of life
questionnaire; HR, BP;
fasting plasma levels of
catecholamines, ANP, BNP,
thiobarbituric acid-reactive
substances, TNF-alpha;
CTR (cardio-thoracic ratio)
on chest X-ray; usual
ECHO parameters; brachial
artery diameter and
ow-mediated dilation
using Doppler ultrasound
Positive,
decreased SBP (𝑝 = 0.019),
decreased CTR on CXR
(𝑝 = 0.002), decreased
LVE DD (l e  ve ntr i cul ar
end-diastolic dimension)
on ECHO (𝑝 = 0.047),
decreased plasma BNP
levels (𝑝 = 0.005),
improved ow-mediated
dilation of brachial artery
on Doppler USS
(𝑝 = 0.0006)insauna
group compared to control
None

Imamura et
al. []
III
Clinical study
with control
group
Increased CVD
risk/Japan  FIR  weeks
Control group
/ without
any CVD risk
factors
Body wt, HR, BP; fasting
serum levels of HCT, Lipid
prole, uric acid, glucose,
thiobarbituric acid-reactive
substances;
ow mediated dilation of
brachial artery using
Doppler USS;
nitroglycerin-induced ow
mediated dilation of
brachial artery using
Doppler USS
Positive,
SBP and DBP reduced
(𝑝 < 0.01,𝑝 < 0.05); body
wt reduced (𝑝 < 0.05);
fasting glucose levels
decreased (𝑝 < 0.05); %
ow mediated dilation of
brachial artery improved
(𝑝 < 0.001)insaunagroup
but no statistical report of
comparisons with control
group
None
CVD = cardiovascular disease; CHF = congestive heart failure; IHD = ischaemic heart disease; PAD = peripheral arterial disease; FIR = far-infrared sauna; VSD = ventricular septal defect; NYHA = New York Heart
Association grading for CHF; temp = temperature; HR = heart rate; SBP = systolic blood pressure; DBP = diastolic blood pressure; wt = body weight; ECHO = echocardiogram; VAS = visual analogue scale; FBG =
fasting blood glucose; BNP = B-natriuretic peptide; HCT = haematocrit.

Evidence-Based Complementary and Alternative Medicine 
T : Sauna studies of rheumatological disease/chronic pain/depression.
Study characteristics Study sample Intervention Comparators Health eects Adverse side
eects
Author &
year
Level of
evidence Design Pop/country 𝑁Sauna type Duration Comparator/
controls
Outcome
measures
Positive/
negative/
negligible
None/mild/
moderate/
severe

Kanji et al.
[]
IRCT
Chronic tension
headache/New Zealand 
Multiple
types,
sauna
voucher
cards
weeks
Control group
received advice
and education
NPRS (numeric pain
rating scale), BDI (Beck
Depression Inventory),
HDI (Headache
Disability Index)
Positive,
% reduction in HA
intensity in  weeks of
treatment arm. Mean
change in headache
intensity between sauna
andcontrolgroup=.
points (% CI
.–.; 𝐹= .; df =
,; 𝑝 = 0.002)
None

Masuda et
al. []
I RCT Chronic pain/Japan  FIR  weeks
Control group
received same
course of
behavioural
counselling,
CBT,
rehabilitation,
and exercise
therapy
VAS for pain; pain
behaviour assessment by
researchers with -item
questionnaire; Zung SDS
(self-rating depression
scale); anger scoring
with CMI (Cornell
Medical Index); sleep
quality with simple –
scoring; degree of
satisfaction of treatments
with simple numerical
scoring; return to work 
years aer intervention
Positive,
increased likelihood of
return to work  years
later (𝑝<0.05); decrease
in anger scoring in sauna
group compared to
control (. ±. to . ±
., 𝑝 < 0.001)
Moderate,
 patients
excluded -could
not tolerate sauna
-acutebronchitis
and
claustrophobia

Masuda et
al. []
IRCT
Mild
depression/
Japan
 FIR  weeks
Control group
received
placebo,
 min bedrest
at ∘Cand
postrest shower
in addition to
the same rehab
programs,
physical therapy,
occupational
therapy
Somatic complaints with
CMI (Cornell Medical
Index);
Zung SDS (self-rating
depression scale); VAS
for hunger and
relaxation; plasma levels
of ghrelin, glucose,
catechol-amines; daily
caloric intake.
Positive,improved
somatic complaints
(𝑝 < 0.001), improved
hunger scores
(𝑝 < 0.0001), and
improved relaxation
scores (𝑝 < 0.0001)in
sauna group compared
to control group. Plasma
ghrelin concentrations
and daily caloric intake
increased in sauna group
(∗𝑡= −2.32,𝑝<0.05
and ∗𝑡= −2.65,𝑝<0.05,
respectively); ∗𝑡=
Student -tailed 𝑡-test
None

 Evidence-Based Complementary and Alternative Medicine
T   : C ont i nued .
Study characteristics Study sample Intervention Comparators Health eects Adverse side
eects
Author &
year
Level of
evidence Design Pop/country 𝑁Sauna
type Duration Comparator/
controls
Outcome
measures
Positive/
negative/
negligible
None/mild/
moderate/
severe

Oosterveld
et al. []
III
single-
group
(side-by-
side)
intervention
pilot trials
Rheumatoid arthritis
(RA) and
ankylosing spondylitis
(AS)/e Netherlands
 FIR  weeks
No control
group; two
groups
receiving
same sauna
intervention
VAS, EPM-ROM (Escola
Paulista de Medicina range
of motion), DUTCH-AIMS
(Dutch arthritis impact
measurement scales),
BASMI (Bath Ankylosing
Spondylitis functional
index of range of motion),
BASDAI (Bath Ankylosing
Spondylitis disease activity
index); serum ESR
Positive,
pain and stiness
decreased in RA
(𝑝<0.05)andAS
(𝑝<0.001)groups
during sauna sessions
only.
Mild-
−% scoring
uncomfortable on
well-being scores
during beginning
of sauna

Amano et
al. []
III
Clinical
study with
control
group, pilot
trial
Females with chronic
fatigue
syndrome/myalgic
encephalomyelitis/Japan
 FIR  weeks
/ chose
not to
undergo
sauna
intervention
SF- survey; SRQ-D (brief
self-rating questionnaire
for depression); STAI
(state-trait anxiety
inventory questionnaire)
Positive,
/ in sauna group
improved during
sessions; / were still
improved at follow-up
− months aerwards;
/ non-responders.
/ controls receiving
usual treatment
improved at follow-up
Moderate-
heat intolerance in
most participants,
protocol changed.

Soejima et
al. []
III
Single-
group
clinical
study
Chronic fatigue
syndrome (CFS)/Japan  FIR  weeks No control
group
Numerical rating scales for
fatigue and POMS (prole
of mood states)
questionnaire
Positive, decreased
fatigue (𝑝=0.002),
improved POMS scores
for anxiety (𝑝 = 0.008),
depression (𝑝 = 0.018),
fatigue (𝑝=0.005)and
performance status
(𝑝=0.005)aersauna
None

Mat-
sumoto et
al. []
III
Single-
group
clinical
study
Females with
bromyalgia and
autoimmune
disorders/Japan
 FIR  weeks
Sauna only
one part of
intervention;
combined
with
underwater
exercise
therapy; no
control group
VAS-visual analogue scale;
no. of tender pts on clinical
exam; FIQ (bromyalgia
impact questionnaire);
SF- quality of life
questionnaire
Positive, reduced VAS
pain scores (𝑝 < 0.001);
fewer  of tender pts
(𝑝<0.01); reduced
symptoms based upon
FIQ (𝑝 < 0.001);
improved quality of life
on SF- questionnaire
(𝑝<0.01–.) aer
combined sauna +
underwater exercise
therapy
None
FIR = Far-infrared sauna; ESR = erythrocyte sedimentation rate; VAS = visual analogue scale; CBT = cognitive behavioural therapy.

Evidence-Based Complementary and Alternative Medicine 
T : Airway conditions and repeated sauna therapy.
Study characteristics Study sample Intervention Comparators Health eects Adverse side
eects
Author & year Level of
evidence Design Pop/
country 𝑁Sauna
type Duration Comparator/
control
Outcome
measures
Positive/negative/
negligible
None/mild/
moderate/
severe
-
Kunbootsri et al.
[]
IRCT
Allergic Rhinitis/
ailand  ai/Finnish  weeks
Control group
received
education and
usual medical
care
HRV, peak nasal
inspiratory ow
and usual
spirometry
parameters
Positive,
reduced high-freq
component (𝑝 = 0.003),
increased low-freq
component (𝑝 = 0.003),
increased low freq: high
freq ratio (𝑝 = 0.003)in
HRV analysis; peak
nasal inspiratory ow
improved (. L/s ±
. to . L/s ±.,
𝑝 = 0.002); FEV1
(forced expiratory
volume at  sec)
improved (.% ±.%
to .% ±.%,
𝑝 = 0.002)insauna
groupcomparedwith
control group.
None
-
Pach et al. [] I
RCT –
Single
blinded
Coryza/
common cold
symptoms/
Germany
 Finnish  days
Face mask
breathing hot
dry air at ∘C,
%RHin
treatment
group; Face
mask breathing
cool, dry air at
∘C, % RH
in control group.
Symptom severity
scoring (–) on
four dierent days;
intake of common
cold medications
daily during week
of intervention.
Negligible,
on day  only, signicant
decrease in symptom
severity in treatment vs
control group [−.
(−.–−.), 𝑝 = 0.04,
% CI] but was not
sustained through day ,
,  assessments.
Less cold medication
takenondayonly[%
(–%) vs % (–%)]
in treatment vs control
group (𝑝 = 0.01,%
CI).
Mild,
cough directly
stimulated by
face mask in
both groups (
in treatment
group;  in
control group).

 Evidence-Based Complementary and Alternative Medicine
T   : C ont i nued .
Study characteristics Study sample Intervention Comparators Health eects Adverse side
eects
Author & year Level of
evidence Design Pop/
country 𝑁Sauna
type Duration Comparator/
control
Outcome
measures
Positive/negative/
negligible
None/mild/
moderate/
severe
-
Kikuchi et al.
[]
II
Controlled
intervention
trial
COPD/
Japan  FIR  weeks
Control group
received usual
medical care
Spirometry
parameters;
 MWT (-minute
walk test); modied
Borg dyspnea scale;
oxygen saturation;
PR
Positive,
between-group
improvements in FEF50
(forced expiratory ow
aer % of expired
forced vital capacity) in
sauna group [+. L/s
(.–. L/s)] vs
control group [−. L/s
(−.–. L/s)],
𝑝 = 0.019.
None
-
Umehara et a l.
[]
III
Single group
intervention,
pilot study
Male COPD
Ex-smokers/
Japan
 FIR  weeks No control
group
BP, PR, body wt,
body temp; usual
ECHO parameters;
exercise tolerance
by bicycle
ergometer; SGRQ
(St. George’s
Respiratory
Questionnaire)
symptom scores;
plasma BNP, HCT,
albumin
before/aer
treatment.
Positive,
decreased SBP and DBP
(𝑝 = 0.002–.);
improvements in RV
function via increased
pressure dierential
(𝑝 = 0.024); Pulmonary
artery pressure during
exercise decreased
(𝑝 = 0.028); increased
exercise time ( s ±
sto s± s,
𝑝 = 0.032); lowest SpO2
during exercise
increased (𝑝=0.022);
symptom scores
improved (. pts ±
. to . pts ±. pts,
𝑝 = 0.002)aersauna.
None
COPD = chronic obstructive pulmonary disease; FIR = far-infrared sauna; PR = pulse rate; HR = heart rate; BP = blood pressure; SBP = systolic blood pressure; DBP = diastolic blood pressure; wt = weight; temp
= body temperature; HRV = heart rate variability; freq = frequency; RH = relative humidity; ECHO = echocardiogram; BNP = B-natriuretic peptide; E/LFTs = electrolytes with liver function tests.

Evidence-Based Complementary and Alternative Medicine 
T : Repeated sauna and athletes.
Study characteristics Study sample Intervention Comparators Health eects Adverse side
eects
Author &
year
Level of
evidence Design Pop/country 𝑁Sauna type Duration Comparator/
controls
Outcome
measures Positive/negative/negligible
None/mild/
moderate/
severe

Stanley et al.
[]
III
Single-group,
interrupted
time series
study
Elite
Athletes–
Males/
Aust ralia
 Finnish  days No control
group
Plasma volume changes
(calculated from Hb
readings); hydration status
(using urine SG by digital
refractometer);
ergometer exercise
performance measures;
HRV
Positive,
postexercise sauna bathing
increased plasma volume
aer  days of intervention
(𝑝 < 0.01)
Mild –
comments of “hot
and very
uncomfortable,
but tolerable” per
thermal comfort
survey conducted
every  min
during sauna
sessions

Zinchuk and
Zhadzko []
III
Single-group
interventional
study
Male Elite
Athletes/
Belarus
 Finnish  months No control
group
Axillary temp; venous
blood gas analysis; lipid
peroxidation and free
radical processes by UV
and uorescence analysis of
plasma and RBCs;
antioxidant estimation by
𝛼-tocopherol uorescence
analysis of plasma and RBC
catalase activity; nitric
oxide metabolism by
spectrophotometric
methods, plasma nitrate
and nitrite levels
Positive, increased axillary
body temp .∘C
(𝑝 < 0.001)aerrstsauna
and .∘C(𝑝<0.002)aer
course of sauna; increased
pH by .% (𝑝 < 0.001),
decreased base excess by
.% (𝑝 < 0.001),
increased venous O2by
.% (𝑝 < 0.001),
increased Hb concentration
in blood by .%
(𝑝 < 0.001), right shi of
oxy-Hb dissociation curve
(decreased anity –
favours release of O2to
tissues) aer st sauna;
similar changes aer nal
sauna
(𝑝 < 0.043–𝑝 < 0.005)
None
RH = relative humidity; Hb = haemoglobin; SG = specic gravity; HRV = heart rate variability; temp = temperature; O2= oxygen; ROS = reactive ox ygenated species; RBCs = red blood cells or er ythrocytes.

 Evidence-Based Complementary and Alternative Medicine
T : Sauna studies of healthy populations.
Study characteristics Study sample Intervention Comparators
Health eects Adverse side
eects
Author &
year
Level of
evidence Design Pop/country 𝑁Sauna type Duration Comparator/
control
Outcome
measures

Pilch et al.
[]
II
Two g roup
clinical
Interventional
study
Healthy
females/
Poland
 Finnish  weeks
Group 
intervention-
sauna × min;
group 
intervention-
sauna ×
 min
HR, SBP, DBP, tympanic
temp, rectal temp, wt;
exhaled air analysis for O2
uptake, CO2exhalation,
respiratory quotient; blood
analysis for Hb, HCT, calc
plasma volume changes,
lipid panel, free fatty acids,
totalfreefattyacids–all
measured before/aer st
sauna and nal sauna
Positive, reduced total
cholesterol (𝑝 < 0.05),
reduced LDL cholesterol (𝑝
value unclear), increased
HDL cholesterol (𝑝 < 0.05)
claimed (reported numbers
do not agree) in group 
aer repeat sauna.
None

Kowatzki et
al. []
II
-group
side-by-side
clinical
interventional
study
Healthy men
and women/
Germany
 Finnish
Minimum
one month of
weekly sauna
use in
“regular
sauna group”
Two g roups
receive the same
-session sauna
intervention:
Group :“regular
sauna group”
before
intervention
Group :
“newcomer
sauna group”
with no prior
sauna  months
before
intervention.
TEWL (trans epidermal
water loss); stratum
corneum hydration; skin
erythema; skin surface pH;
surface sebum content;
ionic concentration of NaCl
in sweat
Positive,
baseline values (pre-sauna)
of forehead sebum level
% lower in regular sauna
group (𝑝 < 0.05); sebum
levels decreased similarly in
both groups; decrease in
NaCl sweat concentration
in regular sauna group only
(∼ mmol/L to
∼ mmol/L, 𝑝 = 0.0167);
skin surface pH lower in
regular sauna group but
similar elevations with
sauna activity.
None

Evidence-Based Complementary and Alternative Medicine 
T   : C ont i nued .
Study characteristics Study sample Intervention Comparators
Health eects Adverse side
eects
Author &
year
Level of
evidence Design Pop/country 𝑁Sauna type Duration Comparator/
control
Outcome
measures

Pilch et al.
[]
II
Two g roup
clinical
interventional
study
Healthy
women/
Poland
 Finnish  weeks
Group 
intervention-
sauna × min;
group 
intervention-
sauna ×
 min
HR, BP, rectal and
tympanic temp, body wt;
blood Hb; calc plasma
volume; serum levels of
TSH, T, T, human
growth hormone, ACTH,
cortisol
Positive,increasedHR,
increased SBP, decreased
DBP and reduced plasma
volumes aer single and
repeated sauna sessions in
both groups
(𝑝 < 0.005–𝑝 < 0.01).
Increased secretions of
growth hormone, ACTH,
cortisol aer single and
repeated sauna sessions in
both groups
(𝑝 < 0.01–𝑝 < 0.05).
None

Gryka et al.
[]
III Single group
clinical study
Healthy
males/
Poland
 Finnish  weeks No control
group
Body mass, HR, Body
skinfold thickness, blood
lipid proles and plasma
volumes
Positive, reduced total
cholesterol (. ±
. mmol/L to . ±
. mmol/L, 𝑝 = 0.02)and
LDL levels (. ±
. mmol/L to . ±.,
𝑝 = 0.01)aersessions
ofsaunaoverweeks–
returned to baseline aer 
weeks without sauna. No
signicant changes in HDL
levels
None

Pilch et al.
[]
III Single group
clinical study
Healthy
females/
Poland
 Finnish  weeks No control
group
Tympanic temp, rectal
temp, wt; plasma levels of
Hb,HCT,lipidpaneland
free fatty acids
Positive, reduction in total
cholesterol (. ±
. mmol/L to . ±
. mmol/L, 𝑝 < 0.05)and
LDL levels (. ±
. mmol/L to . ±
. mmol/L, 𝑝<0.05)
aer repeated sauna
None
HR = heart rate; SBP = systolic blood pressure; DBP = diastolic blood pressure; temp = body temperature; wt = body weight; Hb = haemoglobin; HCT = haematocrit;calc=calculated;lipidpanel=totalcholesterol,
triglycerides/triacylglycerols, high-density lipoproteins, low-density lipoproteins; NaCl = sodium chloride. ACTH = adrenal corticotrophic hormone.

 Evidence-Based Complementary and Alternative Medicine
T : Repeat sauna therapy and detoxication.
Study characteristics Study sample Intervention Comparators Health eects Adverse side
eects
Author & year Level of
evidence Design Pop/country 𝑁Sauna type Duration Comparators/
controls Outcome measures Positive/negative/
negligible
None/mild/
moderate/
severe
-
H¨
uppe et al.
[]
IRCT
Symptomatic
patients with
elevated
serum levels
of lipophilic
toxicants
(PCBs, DDT,
DDE)/
Germany

Two t ype s:
Sauna I (∘C,
% RH) and
Sauna II (∘C,
% RH)
weeks
groups:
(I) - Steam
sauna +
physiotherapy +
oral and
intravenous
detox
supplements
(II) - Dry sauna
+ physiotherapy
+ placebo oral
and placebo
intravenous
supplements
(III) - No sauna
or oral/IV
treatment
Psychologist
(blinded)-assessed and
self-assessed scoring using
validated tools: somatic
symptom complaint list
scoring, Beschwerden-Liste
-item questionnaire;
general depression scoring
using ADS-L/CES-D
-item questionnaire;
SF- quality of life
questionnaire;
neuropsychological
processing speed with
GT-MT/ZVT scoring;
concentration with
“attention test d”; memory
power and speed with
WL-N and
WL-G scoring; serum levels
of PCB congeners ×,
HCB, DDT, DDE.
Positive, improvements
in several somatic
well-being scores in
both treatment groups
(I) & (II), as compared
to group (III) with
Duncan post hoc test
suggesting dierences
between Group (I) and
Group (III) (𝑝<0.01)
and between Group (I)
and (II) (𝑝 < 0.05)but
no dierence between
Group (II) and (III)
(𝑝 = 0.21); No
signicant changes in
neuropsychological
testing scores between
the groups (𝑝 > 0.10);
No signicant changes
in serum concentrations
of selected
organochlorides
between the groups
(𝑝 > 0.10).
None

Evidence-Based Complementary and Alternative Medicine 
T   : C ont i nued .
Study characteristics Study sample Intervention Comparators Health eects Adverse side
eects
Author & year Level of
evidence Design Pop/country 𝑁Sauna type Duration Comparators/
controls Outcome measures Positive/negative/
negligible
None/mild/
moderate/
severe
-
Ross and
Sternquist []
III
Retrospective
chart review
and
follow-up
surveys
Symptomatic
police ocers
with
employment-
related drug
and toxicant
exposures/
U.S.A.

Sauna with
full-spectrum
infrared
(∘F)
−weeks No control
group
RAND© SF- (-item
quality of health survey);
FASE -item survey of
symptoms and sleep;
-item neurotoxicity
questionnaire; MMSE; and
review of daily medical
records during therapy.
Positive,improvedpost
treatment SF- scores
compared to
pre-treatment scores
(with -tailed student
𝑡-test paired scores +
Wilcoxon matched pairs
test and sign test,
𝑝<0.001), across all
subscales; Comparing
pre and post completion
of program: fewer “poor
physical health” days
(. vs . days,
𝑝<0.001); fewer “sick
days” (. vs . days,
𝑝<0.001); more sleep
hours(.vs.h,
𝑝<0.001); lessened
neurotoxicity scoring
(. ±. vs / ±
/ points, 𝑝 < 0.001);
no changes in MMSE
(. vs . points,
𝑝=0.122).
Mild,
heat discomfort
FASE = Foundation for Advancements in Science and Education; MMSE = Mini-Mental State Examination; ADS-L/CES-D = Allgemeine Depressions Skala/Centre for Epidemiological Studies Depression Scale;
GT-MT/ZVT = German Trail-Making Test/Zahlenverbindungstest; WL-N = Wortliste Niveau memory power test; WL-G = Wortliste Geschwindigkeit memory speed test; PCB = polychlorinated biphenyls; HCB
= hexachlorobenzene; DDT = Dichlorodiphenyltrichloroethane; DDE = p-dichlorodiphenylethylene.

 Evidence-Based Complementary and Alternative Medicine
T : Repeated sauna and male fertility.
Study characteristics Study sample Intervention Comparators Health eects Adverse
side eects
Author &
year
Level of
evidence Design Pop/country 𝑁Sauna type Duration Comparator/controls Outcome measures Positive/negative/negligible
None/mild/
moderate/
severe

Garolla et al.
[]
II
Single-group,
longitudinal
time-course
study
Healthy
males/Italy  Finnish
sauna  months No control group
Before, aer intervention,
aer  months, aer 
months’ intervention:
semen analysis; plasma sex
hormone levels (LH, FSH,
testosterone, inhibin);
sperm parameters; sperm
chromatin structure
analysis; sperm apoptosis;
sperm heat stress gene
expression with
quantitative real-time PCR
analysis: HIF-𝛼,KDR,
FLT, VEGF, HSP,
HSP, HSF, HSF, HSFY
NEGATIVE -
Post-intervention: lowered
sperm count ( ±. ×
6vs  ±. ×6,
𝑝 < 0.001); lowered sperm
concentration ( ±. ×
6/ml vs  ±. ×
6/ml, 𝑝 < 0.001); fewer
motile sperm
(. ±.% vs . ±.%,
𝑝 < 0.01)withno
dierences noted by 
months post end of sauna
intervention.
No signicant changes in
plasma sex hormones at
any timepoints.
Abnormal sperm
parameters [decrease in
normal histone-protamine
replacement (𝑝<0.05),
abnormal chromatin
condensation (𝑝 < 0.05),
altered mitochondrial
function (𝑝 < 0.01)];
up-regulation of heat-stress
genes [HIF-1𝛼 (𝑝 < 0.001),
KDR (𝑝 < 0.001), FLT
(𝑝 < 0.001), VEGF
(𝑝 < 0.001)] and
up-regulation of heat shock
proteins/factors [HSP
(𝑝 < 0.001), HSP
(𝑝 < 0.001), HSF
(𝑝 < 0.001), HSF
(𝑝 < 0.001), HSFY
(𝑝 < 0.001)] directly aer
sauna intervention but all
changes completely
reversed by  months post
ceasing sauna activity.
None
LH = luteinizing hormone; FSH = follicle stimulating hormone; PCR = polymerase chain reaction; HIF-𝛼= hypoxia-inducible factor I alpha; KDR = kinase insert domain; FLT = fms-related tyrosine kinase;
VEGF = vascular endothelial growth factor; HSP = heat shock protein ; HSP = heat shock protein ; HSF = heat shock factor ; HSF = heat shock factor ; HSFY = heat shock factor Y.

Evidence-Based Complementary and Alternative Medicine 
T : Risk of bias assessment in randomized controlled trials.
Random
sequence
generation
Allocation
concealment
Blinding of
participants
and
personnel
Blinding of
outcome
assessment
Incomplete
outcome data
Selective
reporting Other bias Jadad et al.
score []
Fujita et al.  ×?××✓✓?<
H¨
uppe et al.
 ×?✓✓✓× ?<
Kanji et al.  ✓✓✓✓✓✓✓
Kihara et al.
 ×?××✓??<
Kunbootsri et al.
 ×?××✓✓?<
Kuwahata et a l.
 ×?××✓✓?<
Masuda et al.
 ×?××✓✓×<
Masuda et al.
 -pain ✓?××✓✓×<
Masuda et al.

-depression
×?××✓✓×<
Miyata et al.
 ×?××✓✓?<
Pach et al.  ✓?✓✓✓✓?
Shinsato et al.
 ×?××✓✓?<
Tei et a l .    ✓?×✓✓✓?
✓:lowriskofbias;×: high risk of bias; ?: unclear risk of bias.
totheCochraneCollaborationcriteria[]andaJadadetal.
score >[].NineoftheseRCTsenrolledfewerthan
participants. Table  summarises the assessments of the RCTs
for overall risk of several types of bias.
efollow-uptimeofmanyofthestudieswasrelatively
short, in the order of weeks to months, thereby possibly com-
promising detectability and reporting of long-term health
eects over years.
3.4. Setting and Participant Characteristics. e reviewed
studies included a total of  participants living in 
dierent countries. Over half of the studies ( of )
originated in Japan. e smallest study involved Australian
athletes (𝑛=7) and the two largest studies (both prospective
cohort studies) involved the same cohort of  Finnish men
[,,].Moststudieshadsmallsamplesizeswithoverhalf
( of  studies) involving  or less participants.
e studies involved a range of healthy and disease
populations with  studies of healthy individuals,  studies
of people diagnosed with cardiovascular disease (CVD) or
increased risk for CVD (i.e., congestive heart failure, type 
or type  diabetes mellitus, and peripheral arterial disease), 
studies of patients diagnosed with rheumatological, chronic
pain, or mood disorders,  studies of patients diagnosed with
airway-related disorders (i.e., chronic obstructive pulmonary
disease, allergic rhinitis),  studies of elite athletes, and 
studies of populations overburdened with environmental
toxicants.
3.5. Interventions. Eleven studies investigated the use of
Finnish saunas and  studies utilised infrared sauna inter-
ventions. e remainder  studies used other forms of dry
sauna (ai-style or mixed). Sauna sessions varied from 
minutes to  minutes in single or multiple sessions totaling
 minutes– hours daily, once to several times each week
over study durations that ranged from  days to  months.
e cohort studies followed frequent infrared sauna bathers
for  years and frequent male Finnish sauna bathers for over
 years.
All of the studies involving Finnish-style saunas used
interventions ranging in temperature from  to ∘Cwith
relative humidity levels of –% except H¨
uppe et al. ,
a study comparing detoxication protocols, which employed
a lower temperature sauna at –∘Cwith%relative
humidity for  minutes in one intervention arm [].
Of the  studies involving infrared sauna, all used
far-infrared types except Ross and Sternquist , which
employed a full-spectrum infrared sauna as part of a
detoxication protocol for policemen []. All infrared
sauna studies entailed sauna exposures at ∘C for –
minutes with the exception of two studies: Amano et al.
 studying the eects of sauna on patients diagnosed

 Evidence-Based Complementary and Alternative Medicine
with chronic fatigue syndrome/myalgic encephalomyelitis
(CFS/ME) using saunas set at ∘C–∘Cforminute
sessions [] and Oosterveld et al.  examining the eects
of sauna set at ∘C for -minute sessions on patients
diagnosed with Ankylosing Spondylitis and Rheumatoid
Arthritis [].
All of the sauna interventions were conducted in super-
vised settings (i.e., in-hospital, rehabilitation hospitals, health
centres, university or medical laboratories, and outpatient
programs) except Kanji et al. , which provided sauna
voucher cards to allow participants to attend saunas of choice
attached to local swimming pools [] and the two large
cohortstudiesthatfollowedFinnishmenattendingsaunasof
their choice [, ].
3.6. Outcome Measures. Some studies focused solely on
measuring subjective quality of life and symptom scoring
surrounding sauna activity such as SF- (-item short
form health survey); FASE (Foundation for Advancements
in Science and Education) -item survey of symptoms and
sleep, CMI (Cornell Medical Index) survey of somatic com-
plaints; VAS (visual analogue scales) for hunger, relaxation,
and specic types of pain (i.e., leg pain); various numeric
rating scales for pain, fatigue, sleep quality, and common cold
symptoms; validated tools for depression, anxiety, headache
disability,andangersuchasPOMS(proleofmoodstates)
questionnaire, BDI (Beck Depression Inventory), SRQ-D
(self-rating questionnaire for depression), Zung SDS (self-
rating depression scale), STAI (state-trait anxiety inventory
questionnaire), and HDI (Headache Disability Index) [, ,
,,,].
Other interventional studies focused on obtaining objec-
tive measures related to sauna activity. For example, the
studies involving CHF patients tracked combinations of
physiological changes using body weight, body temperature,
HR (heart rate) or PR (pulse rate) and SBP and DBP
(systolic and diastolic blood pressures); exercise tolerance
using the  MWD (-minute walking distance) and peak VO2
(peak/maximum volume of oxygen) on bicycle ergometer;
cardiomegaly/heart enlargement using CTR (cardiothoracic
ratio) on CXR (chest X-ray); cardiac ow performance
using standard ECHO (echocardiogram) Doppler ultra-
sound parameters; overall functional state using clinician-
based NYHA (New York Heart Association) classication;
endovascular reactivity using FMD (ow-mediated dilation
of brachial artery); heart failure activity using plasma levels
of BNP (B-natriuretic peptide); autonomic nervous system
and immune-mediated activity using ECG (electrocardio-
gram) recordings with heart rate variability parameters and
plasma levels of norepinephrine, TNF-𝛼(tumour necrosis
factor-alpha), and CD+ (cluster of dierentiation , bone
marrow derived) cells; endovascular activity using plasma
levels of VEGF (vascular endothelial growth factor), nitric
oxide metabolites (nitrate and nitrite), and reactive oxygen
metabolites (hydroperoxide) [–, , , , , , ].
Studies involving patients with increased cardiovascular risk
or studies of healthy patients with aims of detecting changes
in cardiovascular risk with sauna activity used some of the
same physiological parameters mentioned above as well as
serum lipid proles (total cholesterol, LDL, HDL, and triglyc-
erides), fasting plasma glucose levels, serum levels of uric
acid (potential marker of insulin resistance and metabolic
syndrome), plasma levels of ghrelin, serum levels of leptin,
plasma levels of Hb (hemoglobin) and HCT (haematocrit),
and urinary prostaglandin levels [, , , , , ].
Other specic objective outcome measures performed
before/aer sauna include myocardial perfusion scintigraphy
with adenosine, treadmill exercise stress test results, ow-
mediated vasodilation of brachial artery, and expression
of CD-positive bone marrow-derived cells in hospital
patients with ischemic heart disease and total coronary
occlusion; standard spirometry parameters, peak nasal inspi-
ratory ows, and ECG (electrocardiogram) with HRV (heart
rate variability) parameters in participants diagnosed with
allergic rhinitis; plasma volume changes (calculated from
hemoglobin readings), hydration status using urine specic
gravity, exercise performance on ergometer, and ECG with
HRV parameters in elite athletes; axillary body tempera-
tures, venous blood gas panels, lipid peroxidation by UV
(ultraviolet light) and uorescence analysis, and nitric oxide
levels in elite athletes; transepidermal water loss, stratum
corneum hydration, skin erythema, skin surface pH, surface
sebum contents, and NaCl (sodium chloride) concentrations
in sweat of healthy men and women; basic physiological
observations (temperature, heart rate, blood pressure, and
body weight), calculated plasma volumes, and serum levels
of thyroid function (TSH (thyroid stimulating hormone),
T, and T) and other hormones (human growth hor-
mone, adrenocorticotropic hormone, and cortisol) in healthy
women; and pre-and postintervention semen analysis includ-
ing standard sperm parameters, sperm chromatin structure
analysis, sperm apoptosis, quantitative sperm heat-stress
gene expression levels, and plasma levels of male sex hormone
levels (LH (luteinizing hormone), FSH (follicle stimulating
hormone), testosterone, and inhibin) in healthy men.
Other interventional studies employed a combination of
subjective and objective measures. Shinsato et al.  and
Tei et al.  compared VAS for leg pain as well as  MWD
(-minute walking distance), ABI (ankle/brachial index), leg
blood ows with Doppler laser imaging and angiography,
gene expression levels of CD+ blood cells and serum levels
of VEGF, and nitrates and nitrites in patients hospitalised
with peripheral artery disease [, ]. Kikuchi et al.  and
Umeharaetal.assessedmodiedBorgdyspnoeascale
or SGRQ (St George’s Respiratory Questionnaire) in addition
to basic physiological observations (temperature, BP, HR,
respiratory rate, and O2saturation), standard spirometry and
ECHO parameters,  MWD or ergometer exercise tolerance,
andplasmalevelsofBNP,HCT,andalbumininhospi-
talisedpatientswithCOPD[,].Oosterveldetal.
utilised subjective VAS and validated tools of EPM-ROM
(Escola Paulista de Medicina-range of motion), DUTCH-
AIMS (Dutch arthritis impact measurement scales), BASMI
(Bath Ankylosing Spondylitis functional index range of
motion),andBASDAI(BathAnkylosingSpondylitisdisease
activity index), as well as serum levels of ESR (erythrocyte
sedimentation rate) []. H¨
uppe et al.  used several