Table 3: Airway conditions and repeated sauna therapy.

Study characteristics Study sample Intervention ComparatorsHealth effectsAdverse side effects
Author & yearLevel of evidenceDesignPop/
country
Sauna
type
DurationComparator/
control
Outcome
measures
Positive/negative/
negligible
None/mild/
moderate/
severe

2013-
Kunbootsri et al. [57]
IRCTAllergic Rhinitis/
Thailand
26Thai/Finnish6 weeksControl group received education and usual medical careHRV, peak nasal inspiratory flow and usual spirometry parametersPositive,
reduced high-freq component (), increased low-freq component (), increased low freq: high freq ratio () in HRV analysis; peak nasal inspiratory flow improved (119.2 L/s ± 46.4 to 161.9 L/s ± 46.7, ); FEV1 (forced expiratory volume at 1 sec) improved (77.5%  ± 9.8% to 95.6%  ± 5.7%, ) in sauna group compared with control group.
None

2010-
Pach et al. [58]
IRCT –
Single blinded
Coryza/
common cold symptoms/
Germany
157Finnish3 daysFace mask breathing hot dry air at 90°C, 20% RH in treatment group; Face mask breathing cool, dry air at 24°C, 20% RH in control group.Symptom severity scoring (0–10) on four different days; intake of common cold medications daily during week of intervention.Negligible,
on day 2 only, significant decrease in symptom severity in treatment vs control group [−1.0 (−2.0–−0.1), , 95% CI] but was not sustained through day 3, 5, 7 assessments.
Less cold medication taken on day 1 only [3% (1–9%) vs 15% (8–28%)] in treatment vs control group (, 95% CI).
Mild,
cough directly stimulated by face mask in both groups (2 in treatment group; 1 in control group).

2014-
Kikuchi et al. [59]
IIControlled intervention trialCOPD/
Japan
20FIR4 weeksControl group received usual medical careSpirometry parameters; 6 MWT (6-minute walk test); modified Borg dyspnea scale; oxygen saturation; PRPositive,
between-group improvements in FEF50 (forced expiratory flow after 50% of expired forced vital capacity) in sauna group [+0.08 L/s (0.01–0.212 L/s)] vs control group [−0.01 L/s (−0.075–0.04 L/s)], .
None

2008-
Umehara et al. [60]
IIISingle group intervention, pilot studyMale COPD
Ex-smokers/
Japan
13FIR4 weeksNo control groupBP, 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/after treatment.
Positive,
decreased SBP and DBP (–0.0002); improvements in RV function via increased pressure differential (); Pulmonary artery pressure during exercise decreased (); increased exercise time (360 s ± 107 s to 392 s ± 97 s, ); lowest SpO2 during exercise increased (); symptom scores improved (59.7 pts ± 16.9 to 55.3 pts ± 17.2 pts, ) after sauna.
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.