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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 benets 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 eects of repeated
dry sauna interventions on human health. Methods. A systematic search was made of medical databases for studies reporting on
the health eects 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 benecial health eects. 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 benets. More data of higher quality is needed on the frequency and extent of adverse side eects. Further study is
also needed to determine the optimal frequency and duration of distinct types of sauna bathing for targeted health eects and the
specic clinical populations who are most likely to benet.
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 dierent 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 aer sauna bathing.
Sauna bathing is inexpensive and widely accessible with
Finnish-style saunas more oen 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 diculty exercising (e.g., obesity,
chronic heart failure, chronic renal failure, and chronic
liver disease) []. Facilities oering sauna bathing oen
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 benets that include detoxication, 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 eects [, –].
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 eects 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
inammation 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 eects 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 eects is still being explored [, , , –
].
e following systematic review was undertaken to
explore recent research on the clinical eects 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
benets and/or adverse eects 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 eects related to regular, multiple sessions of sauna
activity rather than single sauna sessions, to better reect 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 dierential 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
dierences 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 reecting 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. Aer 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 identied 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 eects. 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
aer title/abstract screen
168 articles retrieved
Same inclusion/exclusion
criteria applied to full text
40 articles included
99 articles excluded
aer 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 conrmed 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 identied, were excluded
aer a review of the abstracts.
Aer 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 identied for further analysis.
In the data extraction step, one study was excluded since
it was essentially a case series with two patients, mistakenly
identied 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) identied, 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 eects Adverse side
eects
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
classication (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/JapanFIRweeks
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 aer a
few sessions
Evidence-Based Complementary and Alternative Medicine
T : C ont i nued.
Study Characteristics Study sample Intervention Comparators Health eects Adverse side
eects
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 prole
and glucose, urinary levels
-epi-prosta-glandin F2𝛼
Positive,
systolic BP (𝑝<0.05)and
urinary -epi-
prostaglandin F2𝛼 levels
(𝑝 < 0.001) signicantly
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 eects Adverse side
eects
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)
aer 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 eects Adverse side
eects
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 aer 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 aer 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 aer sauna
intervention
None
Evidence-Based Complementary and Alternative Medicine
T : C ont i nued.
Study Characteristics Study sample Intervention Comparators Health eects Adverse side
eects
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,
TDM, smoking,
hypercholesterolaemia,
HTN/Japan
FIR weeks
/ control
group without
any lifestyle
diseases
Bodywt,HR,BP,HCT;
fasting serum lipid prole,
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
prole, 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 eects Adverse side
eects
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 aer 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 eects Adverse side
eects
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 stiness
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 aerwards;
/ 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 (prole
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)aersauna
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–.) aer
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 eects Adverse side
eects
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 dierent days;
intake of common
cold medications
daily during week
of intervention.
Negligible,
on day only, signicant
decrease in symptom
severity in treatment vs
control group [−.
(−.–−.), 𝑝 = 0.04,
% CI] but was not
sustained through day ,
, assessments.
Less cold medication
takenondayonly[%
(–%) 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 eects Adverse side
eects
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); modied
Borg dyspnea scale;
oxygen saturation;
PR
Positive,
between-group
improvements in FEF50
(forced expiratory ow
aer % 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/aer
treatment.
Positive,
decreased SBP and DBP
(𝑝 = 0.002–.);
improvements in RV
function via increased
pressure dierential
(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)aersauna.
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 eects Adverse side
eects
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
aer 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)aerrstsauna
and .∘C(𝑝<0.002)aer
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 anity –
favours release of O2to
tissues) aer st sauna;
similar changes aer nal
sauna
(𝑝 < 0.043–𝑝 < 0.005)
None
RH = relative humidity; Hb = haemoglobin; SG = specic 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 eects Adverse side
eects
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/aer 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
aer 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 eects Adverse side
eects
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 aer single and
repeated sauna sessions in
both groups
(𝑝 < 0.005–𝑝 < 0.01).
Increased secretions of
growth hormone, ACTH,
cortisol aer 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 proles and plasma
volumes
Positive, reduced total
cholesterol (. ±
. mmol/L to . ±
. mmol/L, 𝑝 = 0.02)and
LDL levels (. ±
. mmol/L to . ±.,
𝑝 = 0.01)aersessions
ofsaunaoverweeks–
returned to baseline aer
weeks without sauna. No
signicant 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)
aer 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 detoxication.
Study characteristics Study sample Intervention Comparators Health eects Adverse side
eects
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 dierences
between Group (I) and
Group (III) (𝑝<0.01)
and between Group (I)
and (II) (𝑝 < 0.05)but
no dierence between
Group (II) and (III)
(𝑝 = 0.21); No
signicant changes in
neuropsychological
testing scores between
the groups (𝑝 > 0.10);
No signicant 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 eects Adverse side
eects
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 ocers
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 eects Adverse
side eects
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, aer intervention,
aer months, aer
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
dierences noted by
months post end of sauna
intervention.
No signicant 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 aer
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 >[].NineoftheseRCTsenrolledfewerthan
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
eects over years.
3.4. Setting and Participant Characteristics. e reviewed
studies included a total of participants living in
dierent 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 detoxication 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
detoxication 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 eects of sauna on patients diagnosed
Evidence-Based Complementary and Alternative Medicine
with chronic fatigue syndrome/myalgic encephalomyelitis
(CFS/ME) using saunas set at ∘C–∘Cforminute
sessions [] and Oosterveld et al. examining the eects
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 specic 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(proleofmoodstates)
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) classication;
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 dierentiation , 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 proles (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 specic objective outcome measures performed
before/aer 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 specic
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.assessedmodiedBorgdyspnoeascale
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
Evidence-Based Complementary and Alternative Medicine
self-assessed validated scoring tools: Beschwerden-Liste -
item questionnaire of somatic symptoms, ADS-L/CES-D -
item questionnaire of general depression, and SF- quality
of life questionnaire. Objective tests of neuropsychologi-
cal processing speed (GT-MT/ZVT scoring), concentration
(attention test d), memory power and speed (WL-N and
WL-G scoring, resp.), and serum levels of three dierent
PCB (polychlorinated biphenyl) congeners, hexachloroben-
zene, DDT (dichlorodiphenyltrichloroethane), and DDE
(p-dichlorodiphenylethylene) were measured before and/or
aer sauna interventions [].
e two largest prospective cohort studies (𝑛 = 2315)
tracked the incidence of dementia, Alzheimer’s disease,
and other cardiovascular disease-related outcomes such as
sudden cardiac death, fatal coronary artery disease, fatal
cardiovascular disease, and all-cause mortality over +
years, stratied by sauna bathing one time each week, -
times each week, or − times each week [, ]. e one
retrospective cohort study (𝑛 = 129) tracked episodes of
cardiac death, cardiac events, and rehospitalisations due to
congestive heart failure aer completion of an in-hospital -
daysaunaprogramfollowedbytwiceweeklyoutpatientsauna
activity over years [].
3.7. Health Outcomes
3.7.1. Cardiovascular Disease. e ndings of the studies
that researched sauna therapy for congestive heart failure
(CHF)inadultsculminatedinthelargestandmostrecent
prospective multicentred randomized controlled trial involv-
ing patients with advanced CHF that demonstrated small
butimproved-minutewalkingdistances(−. m ±SD
. m, 𝑝 < 0.05), reduced cardiothoracic ratios on chest X-
ray (−.% ±SD .%, 𝑝 < 0.05)reectingreducedheart
sizes, and improved NYHA (New York Heart Association)
classications of disease (fewer class III and IV patients, 𝑝<
0.05) aer weeks of sauna therapy, all compared to no
signicant respective changes in a control group that received
standard medical care [].
A study of infants with ventricular septal defects
(VSDs) and related severe CHF (congestive heart failure) who
underwent sauna bathing for minutes daily for weeks
demonstrated decreased VSD (ventricular septal defect)
shunt ow ratios (𝑝 < 0.05), which averted the need for
surgical repair in infants [].
Another randomized controlled trial examined the eects
of repeated sauna therapy on ventricular arrhythmias in
subjects with congestive heart failure and more than
premature ventricular contractions (PVCs) per hours at
baseline and reported signicantly fewer PVCs (mean
± versus baseline mean ± per hours, 𝑝<
0.01)aerweeksofrepeatedsaunasessionscompared
with no signicant changes in a control group that received
conventional medical therapy [].
Two studies investigated the eects of repeated sauna
sessions on patients with peripheral arterial disease. e
rst study was a pilot trial which reported decreased visual
analogue scale (VAS) pain scores (𝑝 < 0.01), improved -
minutewalkingdistance(MWD)(𝑝 < 0.01), improved
ankle/brachial index (ABI) (𝑝 < 0.01),andanincreaseinvis-
ible collateral vessels in ischemic legs with digital subtraction
angiography (𝑝 < 0.01)observedaerweeksofrepeated
sauna therapy in twenty patients []. e second study was a
randomized controlled trial (𝑛=21)whichreportedsimilar
decreases in VAS (visual analogue scale) leg pain scores (𝑝<
0.05), increases in MWD (𝑝 < 0.01), and improved ABI
(𝑝 < 0.01) in the sauna treatment group compared with
no change in the control group that received conventional
medical therapy. e investigators of this second study also
demonstrated a -fold increase in mRNA CD/GAPDH
expression in peripheral blood mononuclear cells (𝑝 = 0.015)
and increases in serum nitrate and nitrite levels (𝑝 < 0.05,
𝑝 < 0.05) in the sauna group with no respective changes in
the control group and no signicant changes in serum VEGF
levels in either group [].
Another randomized controlled trial examined the eects
of repeated sauna therapy on ischemic heart disease
subjects with chronic total occlusion of coronary arteries
detected on coronary angiogram who had failed or rejected
attempts at percutaneous coronary intervention or who had
vessels deemed unsuitable for operative interventions. is
study revealed that, aer weeks of daily ( times weekly)
infrared sessions, the scoring indices of defect reversibility
on myocardial perfusion scans (summed stress scores and
summed dierence scores) improved ( ±to±, 𝑝<
0.01,and±to±, 𝑝 < 0.01) aer sauna therapy but not
in the control group that received standard medical care [].
e two largest studies of this review which prospectively
followed men in Finland over . years of frequent
saunabathingforcardiovasculardisease-relatedoutcomes
used multivariate analysis and calculated hazard ratios (HR)
adjusting for confounding factors such as blood pressure,
resting heart rate, smoking status, Type diabetes, previous
myocardial infarction, LDL levels, and alcohol consumption.
eir ndings included a % risk reduction [HR .
(.–.), 𝑝 = 0.004] of dementia, a % risk reduction
[HR . (.–.), 𝑝 = 0.03] of Alzheimer’s disease, a %
risk reduction [HR . (.–.), 𝑝 = 0.005] of sudden
cardiac death, and a % risk reduction [HR . (.–.),
𝑝 < 0.001]ofall-causemortality[,].
3.7.2. Rheumatological and Immune-Mediated Disease. A
Dutch study of patients diagnosed with either rheuma-
toid arthritis (RA) or ankylosing spondylitis (AS) reported
decreased pain and stiness in the RA (𝑝 < 0.05)andAS(𝑝<
0.001) groups during weeks of sauna therapy that was not
sustainedaertheweeks,withnochangesindiseaseactivity
beingdetectedineithergroupbaseduponrange-of-motion
scoring and serum levels of ESR (erythrocyte sedimentation
rate) [].
A Japanese single-group study of patients diagnosed
with bromyalgia with or without another rheumatologi-
cal disorder (i.e., systemic lupus erythematosus, systemic
sclerosis, rheumatoid arthritis, Sjogren’s syndrome, Behcet’s
disease, or aortitis syndrome) reported subjective improve-
ments in VAS (visual analogue scale) pain scores (𝑝<
0.001), reduced symptoms based upon FIQ (bromyalgia
impact questionnaire) (𝑝 < 0.001), improved quality of
Evidence-Based Complementary and Alternative Medicine
life indicators on SF- (short form -item) questionnaire
(𝑝 < 0.01–.),andobjectivendingsoffewernumberof
tender points (𝑝 < 0.01) palpated on physical exam aer
weeks of combined far-infrared sauna and underwater
exercise therapy [].
Two studies of patients diagnosed with chronic fatigue
syndrome/myalgic encephalomyelitis reported subjective
improvements aer repeated sauna. Soejima et al. (𝑛=
10) reported decreased fatigue (𝑝 = 0.002)onnumerical
rating scales and improved scores for anxiety (𝑝 = 0.008),
depression (𝑝 = 0.018), fatigue (𝑝 = 0.005), and performance
status (𝑝 = 0.005) on POMS (prole of mood states) ques-
tionnaire aer weeks of infrared sauna sessions []. Amano
et al. (𝑛=15) noted .% of participants receiving
weeks of regular far-infrared sauna therapy improved in
symptomsbaseduponSF-(shortform-item),SRQ-
D (brief self-rating questionnaire for depression), and STAI
(state-trait anxiety inventory questionnaire) compared to
% of participants in the control group, who chose not to
undergo sauna therapy [].
3.7.3. Chronic Pain Syndromes. Two r and omized co ntroll ed
trials investigated the subjective eects of repeated sauna on
chronic pain disorders. One New Zealand study (𝑛=37)of
patients diagnosed with chronic tension headaches reported
a % reduction in headache intensity within weeks of the
sauna treatment arm, with mean change in headache intensity
between sauna and control group being . points (% CI
.–.; 𝐹 = 10.17;df =1,117;𝑝 = 0.002)[].eother
Japanese randomized controlled trial of patients with
chronic pain disorders detected an increased likelihood of
return to work years aer sauna inter vention (𝑝 < 0.05)and
decreases in anger scoring (on CMI, Cornell Medical Index)
in the -week sauna-treated group compared to control
group (. ±. to . ±., 𝑝 < 0.001)whoreceivedthe
same courses of behavioural/rehabilitation/exercise therapy
without additional sauna therapy [].
3.7.4. Depression. One randomized controlled trial that
investigated the eects of weeks of sauna sessions on
patients diagnosed with mild depression reported improved
somaticcomplaints(𝑝 < 0.001), improved hunger scores
(𝑝 < 0.0001), and improved relaxation scores (𝑝<
0.0001) based upon subjective somatic complaint, depres-
sion, hunger, and relaxation scoring in the sauna group
as compared to the control group that received bedrest
instead of sauna therapy. In this same study, plasma ghrelin
concentrations and daily caloric intakes also changed in the
sauna group compared to control group (∗𝑡= −2.32,𝑝<
0.05,and∗𝑡= −2.65,𝑝 < 0.05,resp.)with∗Student two-
tailed group 𝑡-test [].
3.7.5. Lungs and Airways. Two studies focused on the eects
of infrared sauna on patients diagnosed with COPD (chronic
obstructive pulmonary disease). One controlled trial (𝑛=
20)reportedimprovedFEF
50 (forced expiratory ow aer
% of expired forced vital capacity) in patients receiving
weeksofrepeatedsauna[+.L/s(.–.L/s)]versusa
control group [−. L/s (−.–. L/s)], 𝑝 = 0.019,that
received usual medical care. No other changes in spirometry
parameters or -minute walk test distances were detected
between the two groups []. e second study involved a
single group of male, ex-smoker COPD patients (𝑛=13)
with the following ndings aer weeks of sauna sessions:
improved symptom scores (. pts ±. to . pts ±. pts,
𝑝 = 0.002); decreased pulmonary artery pressures during
exercise (𝑝 = 0.028); increased exercise times aer sauna
exposures ( s ± s to s ± s, 𝑝 = 0.032); and
improved oxygen saturation during exercise (𝑝 = 0.022)[].
e ai randomized controlled trial (𝑛=26)that
investigated the eects of a -week rehabilitation sauna
program on patients diagnosed with symptomatic allergic
rhinitis reported improved peak nasal inspiratory ow rates
(. L/s ±. to . L/s ±., 𝑝 = 0.002)andimproved
FEV1(forced expiratory volume at sec) (.% ±.% to
.% ±.%, 𝑝 = 0.002) in the sauna intervention group
compared to a control group that received usual medical care.
e researchers also examined HRV (heart rate variability)
parameters but detected no signicant dierence between the
sauna and control groups [].
Another randomized controlled trial studied common
cold suerers in Germany (𝑛 = 157)sittingforminutes
fully winter-dressed in a Finnish sauna daily over days
breathing in piped “hot dry” sauna air versus control “cool
dry” room temperature air while wearing a face mask.
Only on day assessment, a decrease in symptom severity
scoring was detected in treatment versus control groups [−.
(−.–−.), 𝑝 = 0.04, % CI] but this nding was not
sustained through days , , and of study. Fewer doses of
cold and u medications were taken by the treatment group
on day of assessment [% (–%) versus % (–%), 𝑝=
0.01, % CI], compared to the control group [].
3.7.6. Athletes. Two small noncontrolled interventional trials
studied the physiological eects of repeat sauna in athletes.
One study (𝑛=7) reported that minutes of daily
postexercise sauna bathing for ten days was associated with
peaked expansion of plasma volume aer days (+.%,
% CI: .–.%), followed by a trend back to presauna
levels by days – []. e other study (𝑛=16)noteda
mean postsauna increase in axillary body temp .∘C(𝑝<
0.001)aerrstsaunaversusameanincreaseofonly.
∘C
(𝑝 < 0.002) aer completing a months’ course of sauna
bathing. e researchers also noted postsauna increases in
mean venous pH by .% (𝑝 < 0.001), decreased mean base
excess by .% (𝑝 < 0.001), increased mean venous O2
by .% (𝑝 < 0.001), increased mean Hb concentration
in blood by .% (𝑝 < 0.001), and right shi of oxygen-
hemoglobin dissociation curve (decreased anity, favours
release of O2to tissues) aer the rst sauna with similar
changes in specied parameters noted aer a nal sauna
months later (𝑝 < 0.043–𝑝 < 0.005)[].
3. 7. 7. H e a l t h y Pop u l a t i o n s . Two small uncontrolled, single-
gender studies reported reduced total cholesterol levels (.
±. mmol/L to . ±. mmol/L, 𝑝 = 0.02)andreduced
LDL (low density lipoprotein) levels (. ±. mmol/L to
Evidence-Based Complementary and Alternative Medicine
. ±., 𝑝 = 0.01)inhealthymen(𝑛=16)aerweeks
of regular sauna activity involving min sauna sessions []
and reduced total cholesterol levels (. ±. mmol/L to
. ±. mmol/L, 𝑝 < 0.05)andreducedLDLlevels
(. ±. mmol/L to . ±. mmol/L, 𝑝 < 0.05)in
healthy women (𝑛=9)aerweeksofregularsauna
activity involving -minute sauna sessions []. e same
research group of both studies reported earlier ndings of
signicant increases in heart rate, systolic blood pressure,
growth hormone, adrenocorticotropic hormone, and cortisol
levels along with signicant decreases in diastolic blood
pressure and plasma volumes aer single and repeated sauna
sessions in women aer weeks of either -min sauna
sessions or -min sauna sessions [, ]. Reductions in total
and LDL cholesterol levels along with increased HDL (high
density lipoprotein) cholesterol levels were reported in the
-min sauna group.
Another study of healthy men and women examined the
skin physiology of regular sauna attenders (𝑛=21)compared
to newcomer sauna attenders (𝑛=20) before and aer
sauna bathing. e investigators reported a decrease in NaCl
(sodium chloride) sweat concentrations in the regular sauna
group (∼ mmol/L ±∼ mmol/L to ∼ mmol/L ±∼
mmol/L, 𝑝 = 0.0167) without any respective changes in
the newcomer sauna group. Baseline values (presauna) of
forehead sebum level were % lower in the regular sauna
group (𝑝 < 0.05) compared with newcomer group but sebum
levels decreased similarly in both groups aer sauna. Skin
surfacepHwasgenerallymeasuredtobelowerintheregular
sauna group but similar scales of pH elevation were recorded
for both groups during and aer sauna activity [].
3.7.8. Detoxication. Populations burdened with toxicants
were the subject of two studies. Both entailed multimodal
therapies with sauna as a prominent but not sole intervention
and both demonstrated improved self-assessed quality of life
measures [, ]. Ross and Sternquist (𝑛=69)docu-
mented improved posttreatment SF- (short form -item
health survey) scores in symptomatic policemen exposed
to employment-related drugs and toxicants compared to
pretreatment scores (with -tailed Student 𝑡-test paired scores
and Wilcoxon matched pairs test and sign test, 𝑝 < 0.001),
across all subscales aer − weeks of infrared sauna sessions
with up to hours of sauna bathing daily. e FASE
(Foundation for Advancements in Science and Education)
-item and neurotoxicity symptom questionnaires further
revealed fewer “poor physical health” days (. versus .
days, 𝑝 < 0.001); fewer “sick days” (. versus . days,
𝑝 < 0.001); more sleep hours (. versus . h, 𝑝 < 0.001);
and lessened neurotoxicity scoring (. ±. versus / ±
/ points, 𝑝 < 0.001)[].
e other sauna detoxication study was a randomized
controlled trial (𝑛=36) of symptomatic individuals with
elevated levels of lipophilic toxicants, comparing two separate
sauna interventions with a control group: (I) steam sauna
with oral and intravenous supplements, (II) dry sauna with
substitute placebo oral and intravenous interventions, and
(III) no sauna, no oral, and no intravenous interventions.
Usingmultivariateanalysisofvariance(MANOVA)methods,
several somatic well-being scores improved in both treatment
groups (I) and (II), as compared to group (III) with Duncan
post hoc test suggesting signicant dierences between group
(I) and group (III) (𝑝 < 0.01)andbetweengroups(I)and
(II) (𝑝 < 0.05). No dierences however were seen between
groups (II) and (III) (𝑝 = 0.21) and no signicant changes
in neuropsychological testing scores (𝑝 > 0.10)orserum
concentrations of selected organochlorides (𝑝 > 0.10)were
reported between any of the groups [].
3.7.9. Spermatogenesis. One longitudinal time-course study
examined the eects of Finnish sauna activity on male
sperm and fertility measures in healthy men. Aer
months of repeated sauna (-min saunas twice weekly), the
investigators reported reduced sperm counts ( ±. ×
6versus ±. ×6,𝑝 < 0.001); reduced sperm
concentrations ( ±. ×6/ml versus ±. ×6/ml,
𝑝 < 0.001); fewer motile sperm (. ±.% versus . ±
.%, 𝑝 < 0.01); abnormal sperm parameters [decrease in
normal histone-protamine replacement (𝑝 < 0.05); abnormal
chromatin condensation (𝑝 < 0.05); altered mitochondrial
function (𝑝 < 0.01)]; upregulation of various heat-stress
genes [HIF-𝛼(𝑝 < 0.001), KDR (𝑝 < 0.001), FLT (𝑝<
0.001), and VEGF (𝑝 < 0.001)]; and upregulation of HSPs
(heat shock proteins) and HSFs (heat shock factors) [HSP
(𝑝 < 0.001), HSP (𝑝 < 0.001), HSF (𝑝 < 0.001), HSF
(𝑝 < 0.001), and HSFY (𝑝 < 0.001)].However,allspecied
changes reverted back to normal months aer ceasing sauna
activity and no signicant changes in plasma sex hormones
from baseline were detected directly aer sauna or aer or
months[].
3.7.10. Adverse Side Eects. Of the included studies, only
eight reported any adverse symptoms from sauna bathing.
Six studies recorded adverse eects graded as mild, meaning
symptoms of complaint were noted which did not alter the
study protocol or incur dropouts to the study. Mild heat
discomfort was the major complaint [, , ]. Other mild
complaints noted in one infrared sauna study of heart failure
patients (𝑛 = 149) included symptomatic low blood pressure,
hypovolemia, polyurination, weight loss, and, questionably,
acute bleeding aer a tooth extraction []. Another study of
patients with peripheral arterial disease (𝑛=21)reported
transient leg pain in one participant during a rst infrared
sauna session with the pain improving aer completing a
few sauna sessions and disappearing altogether by the end of
the -week study []. Pach et al. reported coughing in
of Finnish-style sauna participants, stimulated by the
placement of a face mask in both intervention and control
groups, with dierent temperatures of air piped through the
masks of the respective groups [].
Two studies recorded moderate adverse eects, dened
assymptomcomplaintsthatledtodropoutofstudypar-
ticipants or led to changes in study protocols. One study,
involving een women diagnosed with chronic fatigue
syndrome/myalgic encephalomyelitis, reported enough heat
intolerance in “most” of the participants such that the
investigators reduced the temperature of the infrared sauna
Evidence-Based Complementary and Alternative Medicine
intervention from ∘Cto
∘C to nish conducting the study
[]. Another infrared sauna study (randomized controlled
trial) of chronic pain patients (𝑛=46) reported patients
droppingoutofthetreatmentarmduetoacutebronchitisand
claustrophobia experienced in the sauna room []. None of
the included studies reported severe adverse eects involving
the need for emergency medical services.
4. Discussion
4.1. Principal Findings. endingsofthisreviewsuggest
frequent dry sauna bathing improves a variety of subjective
and objective health parameters and that frequent Finnish
sauna bathing is associated with improved outcomes such as
reduced overall mortality and reduced incidence of cardio-
vascular events and dementia, at least in men [, ]. e
most established clinical benets of sauna bathing are asso-
ciated with cardiovascular disease, yet there is also evidence
to suggest that saunas, either Finnish-style or infrared, may
benet people with rheumatic diseases such as bromyalgia,
rheumatoid arthritis, and ankylosing spondylitis, as well as
patients with chronic fatigue and pain syndromes, chronic
obstructive pulmonary disease, and allergic rhinitis. Sauna
bathing may also improve exercise performance in athletes,
skin moisture barrier properties, and quality of life and
is not associated with serious adverse events. ere is not
yet enough evidence to distinguish any particular health
dierences between repeat Finnish-style and repeat infrared
sauna bathing.
Cardiovascular disease has clearly been a focus for sauna
researchers since despite Finnish-style sauna being con-
sidered by some in the past as a contraindication for patients
with CHF and other cardiovascular diseases, most likely
because of perceived intolerance to the high temperatures
[]. Nearly half ( of ) of the studies included in this
review involved populations who had active cardiovascular
disease or increased risk for cardiovascular disease, and all
these studies demonstrated benecial health eects. Seven of
these studies were randomized controlled trials (RCTs),
withonlyoneofthemmeetingtheCochranecriteriafor
an acceptably low risk of bias. is particular multicentre
RCT (𝑛 = 149) reported improvements in all outcome
measures except B-type natriuretic peptide (BNP) levels
(namely, longer -minute walking distance, reduced cardio-
thoracic ratio on chest X-ray, and improved NYHA (New
York Health Association) classication) in the infrared sauna-
treatedcongestiveheartfailuregroupcomparedtocontrol
over only weeks of intervention [].
While sauna bathing appears to show promise as a
lifestyle intervention for cardiovascular disease, a majority
of the cardiovascular disease-related sauna studies ( of )
were conducted by the same core Japanese research group
and aliates who employed “Waon therapy” [], which
involved far-infrared sauna bathing. ese Waon therapy
studies used similar outcome measures and mostly involved
hospitalised patients, which might reect some dierences in
health care systems and thresholds for hospitalisation. e
use of primarily hospitalised patients in these studies also
brings up issues of how applicable the ndings may or may
not be to outpatient populations.
Despite dierences in sauna types, temperature, fre-
quency, and duration of interventions, the far-infrared sauna
studies involving cardiovascular disease and congestive heart
failure patients suggest favourable outcomes that reinforce
earlier ndings of interventional Finnish sauna studies and
cardiovascular disease [–]. is suggests that heat stress,
whether induced by infrared or Finnish-style sauna, causes
signicant sweating that is likely to lead to hormetic adap-
tation and benecial cardiovascular and metabolic eects.
isisfurthersupportedbythetwolargeobservational
studies that found striking risk reductions for sudden cardiac
death (%) and all-cause mortality (%) as well as for
dementia (%) and Alzheimer’s disease (%), in men
whousedasauna−timesperweekcomparedtoonly
once per week [, ]. While these large cohort studies
are based on calculated hazard ratios with adjustments for
common cardiac risk factors, it has been pointed out that
the association between sauna activity and health outcomes
may be noncausal and that sauna use is merely an indicator
of “healthy lifestyle” and other socioeconomic confounding
factors []. Nevertheless, these ndings point to the need
for further study and serious consideration given to sauna
bathing to address the ever-increasing individual, societal,
and nancial burdens of cardiovascular disease as well as
dementia-related conditions in aging populations.
4.2. Mechanisms of Action: Sauna Bathing. Several mecha-
nismsofactionhavebeenproposedforthehealtheects
of frequent sauna bathing. Exposure to heat increases
cardiac output and reduces peripheral vascular resistance
and induces other physiological changes in cardiovascular
parameters such as decreased systolic and/or diastolic blood
pressure [, , , –, , ], increased HRV (heart rate
variability) [, , ], improved cardiac function markers
[,,,,,,,],andimprovedow-mediated
arterio- and vasodilatation of small and/or large blood vessels
[, , , , –]. Regarding hormonal and metabolic
models, reduced levels of epinephrine and/or norepinephrine
[, ], increased levels of nitric oxide metabolites in blood
[, ] and urine [], decreased total and LDL (low density
lipoprotein) cholesterol levels [, , ], increased serum
levels of growth hormone, adrenocorticotropic hormone
(ACTH), and cortisol [], decreased fasting blood glucose
levels [], increased plasma ghrelin levels [], and reduced
urinary levels of prostaglandins (-epi-prostaglandin F2𝛼)
[] have been detected aer regular sauna sessions. Together,
these ndings support complex multipathway end-organ
eects on the central and autonomic nervous system, the
peripheral vascular endothelium, and the hypothalamus-
pituitary-adrenal axis, as well as on the kidneys and the liver
that are continuing to be documented [, , , ].
e complexity of how sauna bathing may inuence
cardiovascular risk factors is suggested by the report of
benecial eects on total cholesterol and LDL (low density
lipoprotein) cholesterol and conicting results on HDL (high
density lipoprotein) levels in healthy young men and women
[,,].esendings,whichneedtobeconrmed
Evidence-Based Complementary and Alternative Medicine
in larger studies with nonsauna control groups, may point
to dierences between Finnish and infrared saunas as they
contrast with previous similarly sized, yet better controlled
studies of infrared sauna bathing in populations at increased
risk of cardiovascular disease [, , ]. ese ndings
may also be compared to the metabolic eects of exercise
in healthy populations which include improvements in both
LDLandHDLlipidlevels[].
Whiletherearelikelytobemanymechanismsofaction
inuencing the physiological eects of sauna bathing, it has
been suggested that sauna bathing may induce a general
stress-adaptation response that leads to “hormetic adap-
tation” and the establishment of “sauna tness,” possibly
analogous to the hormetic adaptation responses of exercise.
isissupportedbynewer,single-cellanalysismethodsthat
suggest sauna bathing increases generation of free radicals
andreactiveoxygenatedspeciesalongwithenhancedantiox-
idant activities via proposed nitric oxide- (NO-) dependent
processes in blood [] and upregulation of specic HSPs
(heat shock proteins) and HSFs (heat shock factors) in semen
[]. e two studies in athletes further support sauna’s
involvement in hormetic stress responses with the ndings
of plasma volume expansion aer days of daily postexercise
sauna bathing, followed by a trend back to presauna levels
by days – in one study [], along with mean postsauna
increases in axillary body temperature of .∘Caerarst
sauna versus mean postsauna increases of only .∘Caer
the last session of a -month course in the other study [].
Additionally, increases in plasma lipid peroxidase levels and
increases in free radical processes of RBCs and decreases
in plasma 𝛼-tocopherol (antioxidant) levels and decreases
in RBC catalase activity aer an initial sauna were not
maintained aer months of regular sauna [], suggesting
that sauna bathing may upregulate antioxidant defences.
Improved adaptation to stress with regular sauna bathing
may be further enhanced by excretion of toxicants through
heavy sweating. Many industrial toxicants including heavy
metals, pesticides, and various petrochemicals may be
excreted in sweat leading to an enhancement of metabolic
pathways and processes that these toxic agents inhibit [].
Sweat-induced excretion of toxic metals such as arsenic,
cadmium, lead, and mercury has been reported with the rates
of excretion matching or exceeding urinary routes []. ere
is also recent evidence that toxic chemicals and xenobiotics
such as polybrominated diphenyl ether (PBDE) ame retar-
dants, organochlorine pesticides, bisphenol-A (BPA), and
phthalates may be excreted via induced sweating at rates
that exceed urinary excretion [–]. e importance of
sweat in excretion pathways has been further documented
by sweat-patch technology used to monitor illicit drug use
and is based on dozens of studies of the pharmacodynamics
and pharmacokinetics of amphetamine, cocaine, cannabis,
opiates, and associated metabolites [, ]. While sweat-
induced detoxication certainly occurs, studies using sauna
for detoxication purposes report more favourable ndings
with subjective rather than objective measures [, ].
Further research on sauna-based detoxication is warranted
as the excretory functions of skin via sweating or other active,
passive inter- and/or transcellular, and transdermal pathways
are complex and the role of frequent sweating to promote
excretion and improve health is still poorly dened [].
In addition to having profound physiological eects,
sauna bathing is reported to have benecial psychological
eects that are reected in the many reports of improved
well-being, pain tolerance, and other self-assessed symptom-
relatedscoring[,,,,,–,,,,].
e psychological impact of sauna bathing may be due to
a combination of factors that include release of endorphins
and other opioid-like peptides such as dynorphins [, ],
forced mindfulness, psychological stress reduction, relax-
ation, improved sleep, time out from busy life schedules,
placebo eects, and other aspects of individual psychological
and social interactions that likely occur around frequent
sauna activity. While it is dicult to distinguish between the
dierent factors that produce positive psychological eects,
such eects may enhance other physiological and metabolic
benets as they are likely to promote adherence to regular
sauna activity.
4.3. Safety and Adverse Eects with Sauna. In the medical
literature at large, there are reports of severe adverse eects
from saunas that include dry sauna-induced burns [] and
myocardial ischemia (especially in patients with unstable
coronary artery disease) [], along with less frequent reports
of syncope/falls [], hypersensitivity pneumonitis (“sauna
lung”) [], nonexertional heatstroke [], rhabdomyolysis
[], ocular irritations [], “sauna stroke syndrome” [],
anddeath[].eriskofdeathfromsaunaswasexamined
in retrospective population studies of frequent sauna users
in Sweden and Finland, with the annual death rate from
saunas being reported as . and per , inhabitants,
respectively,withhalformoreofallthesedeathsinvolving
the use of alcohol and a common risk factor of sauna bathing
alone [, ].
In this review, adverse signs and symptoms of both
Finnish-style and infrared sauna bathing were reported as
mild to moderate heat discomfort and intolerance in of the
studies [, , , ], low blood pressure/light-headedness
in one study [], transient leg pain in another study [],
airway irritation in two studies [, ], and claustrophobia in
one study [], with no severe adverse symptoms reported in
any studies. Detailed comparative analysis of adverse eects
between studies was limited by small sample sizes, hetero-
geneity of sauna types and study design (many without con-
trol groups), and inconsistent reporting of adverse side eects
within outcome measures. e highest intensity of adverse
eects (moderate levels of heat intolerance) occurred in
populations aicted with chronic fatigue syndrome, chronic
pain, rheumatoid arthritis, and ankylosing spondylitis. As
these conditions are all associated with inammation and
abnormal immune responses, it may be that the heat and/or
increased sweating of sauna activity is modulating some of
these responses [, , ]. e direct adverse eects of heat
may also be responsible for the impairment of sperm counts,
concentration, and motility and upregulation of heat-stress-
related genes reported in the sperm of healthy men aer
a -month course of Finnish-style sauna []. While these
ndings are based upon one identied study of only men,
Evidence-Based Complementary and Alternative Medicine
thendingsareconsistentwithsomeearlierresearchon
the eects of genital heat stress on semen quality [–].
All the deleterious sperm eects of the sauna intervention
mentioned in this study were observed to revert back to
“normal” presauna levels aer months of avoiding sauna
activity []. While this supports current recommendations
for men seeking to optimize fertility to avoid sauna-type
activities [], further research is required to determine
if similar eects on sperm occur with lower temperature
infrared sauna bathing or if sauna bathing has any eect on
male fertility.
4.4. Strengths/Limitations. To the best of our knowledge, this
is the rst systematic review to include both Finnish-style
and infrared sauna studies. However, we did not include
studies of steam sauna interventions and therefore may have
overlooked some evidence of the eects of heat on health.
Another limitation of this study is the inclusion of only
English language, especially since sauna activity is frequent in
non-English speaking countries. Furthermore, the quality of
the reviewed studies was variable with many studies having
small sample sizes, poorly described methodology, variable
useofcontrols,dieringtypesofsaunaandsaunaprotocols,
variable duration and frequency of sauna interventions, and
inconsistent mention of cooling therapies or rehydration
protocols along with heterogeneous outcome measures. e
great heterogeneity of studies makes meaningful compar-
isons across studies dicult and provides insucient evi-
dence to recommend specic temperature, frequency, or
duration of sauna bathing for any specic health outcome.
In the months since this systematic review was conducted,
a number of new research ndings have been published,
analyzing various subsets of the same Finnish prospective
cohort of over men who regularly sauna-bathed, initially
aged – years, followed over years as part of the KIHD
(Kuopio Ischemic Heart Disease) study, as detailed in two of
the studies included in Table : cardiovascular disease- (CVD-
) related sauna studies. ese newer ndings cite reduced risk
of acute and chronic respiratory conditions [], reduced
risk of pneumonia [], reduced serum levels of C-reactive
protein (marker of systemic inammation) [] with more
frequent sauna bathing, and reduced risk of hypertension
[] and additional improved all-cause mortality when
jointly associated with cardiorespiratory tness []. ese
ndings add further support to the conclusions of this review.
4.5. Future Research Perspectives. With the rise of single-
cell analysis and “omics” platforms of analysis such as
metabolomics and transcriptomics, especially applied to
sweat, blood, urine, saliva, and other human biouids, the
ability to unravel the metabolic pathways at work during
sauna or whole-body thermotherapy will certainly improve.
Further study of these metabolic pathways might also help
to elucidate the stress-related pathways of immune and
inammatory activity that may be involved in conditions
such as chronic fatigue syndrome, chronic pain, rheumatoid
arthritis, and ankylosing spondylitis.
Studies examining heart rate variability (HRV) as an
outcome assessment are increasing and further results may
better inform the physiological models of what is thought
to be happening with repeated sauna of either Finnish or
infrared types. e concepts of hormetic stress and inter-
relating “sauna tness” or habituation to the physiological
eects of repeated sauna activity might have implications for
preventive or therapeutic targets in the future. Conducting
more studies of repeated sauna in healthy but nonathletic
participants may further help to elucidate the similarities and
dierences in metabolic pathways between repeated sauna
activity and regular exercise. Further studies are also needed
to distinguish between the health eects of Finnish saunas,
which oen involve brief periods of increased humidity
and dramatic cooling interventions, compared to the lower
temperature infrared saunas that typically do not have such
variations.
5. Conclusions
Regular infrared and/or Finnish sauna bathing has the
potential to provide many benecial health eects, especially
for those with cardiovascular-related and rheumatological
disease, as well as athletes seeking improved exercise per-
formance. e mechanisms for these eects may include
increased bioavailability of NO (nitric oxide) to vascular
endothelium, heat shock protein-mediated metabolic activa-
tion, immune and hormonal pathway alterations, enhanced
excretions of toxicants through increased sweating, and other
hormetic stress responses.
Currently there is insucient evidence to recommend
specic types of sauna bathing for specic clinical conditions.
While regular sauna bathing appears to be well-tolerated in
the clinical setting with only minor and infrequent adverse
eects reported, further data on the frequency and extent of
adverse eects is required. Further studies are also required
to explore the mechanisms by which sauna bathing exerts
physiological, psychological, and metabolic eects, as well
as to better dene the benets and risks of distinct types
of saunas and the optimal frequency and duration of sauna
bathing for benecial health eects.
Conflicts of Interest
e authors declare that they have no conicts of interest.
Acknowledgments
ismanuscriptwasdevelopedaspartofstudyconducted
by Dr. Joy Hussain during her Ph.D. candidature at RMIT
University. Joy Hussain is supported by a Ph.D. scholarship
from the Jacka Foundation.
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