Physical and Mental Effects of Bathing: A Randomized Intervention Study

Abstract

Showering is the most common form of bathing worldwide. Whole-body immersion bathing in warm water (~40°C) is common in Japan and exerts sufficient hyperthermic action to induce vasodilatation and increase blood flow, supplying more oxygen and nutrients to the periphery. Cross-sectional studies report better subjective health status with an immersion bathing habit. This randomized controlled trial compared the effects on health of immersion bathing and shower bathing in 38 participants who received 2-week intervention of immersion bathing in warm water (40°C) for 10 min (bathing intervention) followed by 2-week shower bathing without immersion (showering intervention) or vice versa (n = 19 each group). Visual analog scale scores were significantly better for fatigue, stress, pain, and smile and tended to be better for self-reported heath and skin condition after bathing intervention than after showering intervention. The SF-8 Health Survey showed significantly better general health, mental health, role emotional, and social functioning scores. Profile of Mood State scores were lower for stress, tension-anxiety, anger-hostility, and depression-dejection. Immersion bathing, but not shower bathing, exerts hyperthermic action that induces increased blood flow and metabolic waste elimination, which may afford physical refreshment. Immersion bathing should improve both physical and emotional aspects of quality of life.

Full text

Research Article
Physical and Mental Effects of Bathing: A Randomized
Intervention Study
Yasuaki Goto ,1Shinya Hayasaka,1,2 Shigeo Kurihara,1and Yosikazu Nakamura3
1ONSEN Medical Science Research Center, Japan Health & Research Institute, 3-1-4 Nihonbashi, Chuo-ku, Tokyo 103-0014, Japan
2Tokyo City University, 8-9-18 Todoroki, Setagaya-ku, Tokyo 158-8586, Japan
3Jichi Medical University, 3311-1 Yakushiji, Shimosa City, Tochigi 329-0498, Japan
Correspondence should be addressed to Yasuaki Goto; yasuakigotoh@gmail.com
Received 8 February 2018; Revised 23 April 2018; Accepted 14 May 2018; Published 7 June 2018
Academic Editor: Albert S. Yeung
Copyright ©  Yasuaki Goto et al. 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.
Showering is the most common form of bathing worldwide. Whole-body immersion bathing in warm water (∼∘C) is common
in Japan and exerts sucient hyperthermic action to induce vasodilatation and increase blood ow, supplying more oxygen and
nutrients to the periphery. Cross-sectional studies report better subjective health status with an immersion bathing habit. is
randomized controlled trial compared the eects on health of immersion bathing and shower bathing in  participants who
received -week intervention of immersion bathing in warm water (∘C) for  min (bathing intervention) followed by -week
shower bathing without immersion (showering intervention) or vice versa (n =  each group). Visual analog scale scores were
signicantly better for fatigue, stress, pain, and smile and tended to be better for self-reported heath and skin condition aer bathing
intervention than aer showering intervention. e SF- Health Survey showed signicantly better general health, mental health,
role emotional, and social functioning scores. Prole of Mood State scores were lower for stress, tension-anxiety, anger-hostility,
and depression-dejection. Immersion bathing, but not shower bathing, exerts hyperthermic action that induces increased blood
ow and metabolic waste elimination, which may aord physical refreshment. Immersion bathing should improve both physical
and emotional aspects of quality of life.
1. Introduction
Lifestyles can vary widely, and several lifestyle factors such as
diet, exercise, sleep, alcohol consumption, and smoking are
associated with health and survival [–]. Another aspect of
lifestyle that varies is bathing, several forms of which include
bathing in a conventional shower, steam shower, sauna, or
bathtub. Bathing in a shower is the most common form of
bathing. In Japan, immersion of the whole body in warm
water (around ∘C) is a common habit [, ]. It is known that
the most benecial eect of so-called immersion bathing is
vasodilation induced by hyperthermic action, which results
in systemic elevation of the supply of oxygen and nutrients
to the periphery and increased elimination of carbon dioxide
and metabolic waste materials [–].
A survey of bathing practices in Japan revealed that
% of participants enjoyed bathing (either in a bathtub or
shower) and more than % reported sensations or feelings of
warmth, relaxation, relief from fatigue, and refreshment aer
immersion bathing []. e weekly frequency of bathing
varies by season: in summer, shower bathing occurs, on
average . times per week versus immersion bathing at .
times (at . ±.∘Cfor.±. min); in winter, immersion
bathing occurs, on average, . times per week (at . ±
.∘Cfor.±. min) and shower bathing at . times
[].
Our previous cross-sectional studies found good sub-
jective health status, sucient sleep and rest, low levels of
stress, and high subjective happiness in individuals who had
a habit of bathing in hot water everyday [, ]. However, the
benetsofcertainperiodsofbathinginterventionshavenot
been reported.
is randomized controlled trial assessed the eects of
a total of  weeks of intervention consisting of  weeks of
immersion bathing intervention (bathing intervention) and
 weeks of shower bathing without immersion intervention
Hindawi
Evidence-Based Complementary and Alternative Medicine
Volume 2018, Article ID 9521086, 5 pages
https://doi.org/10.1155/2018/9521086

 Evidence-Based Complementary and Alternative Medicine
T : Self-reported health status (VAS score) before and aer bathing intervention.
Before Aer Dierence p value
Mean SD Mean SD Mean
Self-reported health . ±. . ±. . <. ∗∗
Skin condition . ±. . ±. . <. ∗∗
Fatigue . ±. . ±. −. <. ∗∗
Stress . ±. . ±. −. <. ∗∗
Pain . ±. . ±. −. <. ∗∗
Smile . ±. . ±. . <. ∗∗
∗∗p<..
T : Self-reported health status (VAS score) before and aer showering intervention.
Before Aer Dierence p value
Mean SD Mean SD Mean
Self-reported health . ±. . ±. . <. ∗∗
Skin condition . ±. . ±. . <. ∗∗
Fatigue . ±. . ±. −. <. ∗∗
Stress . ±. . ±. −. <. ∗∗
Pain . ±. . ±. −. <. ∗∗
Smile . ±. . ±. . <. ∗∗
∗∗p<..
(showering intervention) in order to compare the physical
and mental eects between the two interventions.
2. Materials and Methods
2.1. Sample Preparation. Subjects were  healthy adults
( women,  men; mean age, . years, SD = .). We
recruited the subjects from a Japanese portal site named
KARADAKARA, which was an Internet circle where people
are interested in health consisting of about  thousand
people. e Ethics Committee of Japan Health & Research
Instituteapprovedthestudyprotocol,andallworkwas
conducted in accordance with the Declaration of Helsinki
(). Written informed consent was obtained from each
subject before commencing the study. is study is registered
in the UMIN Clinical Trials Registry (UMIN).
is intervention study was conducted from October
 to November , , to investigate the two bathing
methods of immersion bath in hot water (∘C) for  min
(bathing) and showering without immersion (showering).
Subjects were randomized to the groups, and the eects of
bathing for  weeks and showering for  weeks continuously
were compared using a cross-over method. No washout was
performed.
2.2. Assessment Measures. Perceivedhealthisassociatedwith
mortality [], so self-reported health status (health, skin
condition, pain, fatigue, stress, and smile in the mirror) was
assessed using a -mm visual analog scale (VAS; extremely
bad  [le] to extremely good  [right]) aer bathing
every day during the intervention periods. To assess health
and mood states during each intervention period, partici-
pants retrospectively completed the Japanese versions of the
-item Short Form Health Survey (SF-) and a short form of
the Prole of Mood States (POMS), respectively, aer each
-week intervention period. e SF- [] uses single-item
scales to assess  items: general health, physical functioning,
role limitations due to physical health problems, bodily pain,
vitality (energy/fatigue), social functioning, mental health,
and role limitations due to emotional problems. Physical
and Mental Component Summary scores are also calculated.
e POMS [] is used worldwide for the assessment of
mood states, measuring the constructs of tension-anxiety,
depression-dejection, anger-hostility, fatigue, confusion, and
vigor.
2.3. Statistical Analysis. e paired t-test was used to com-
pare subjective health status before and aer bathing every
day and between the -week bathing intervention and the -
week showering intervention periods. e statistical package
SPSS .J (IBM, Tokyo, Japan) was used for analysis.
3. Results
Subjects of the analysis were  of the  participants who
remained in good health during the -week intervention
study and completed all measurement items without missing
data.Fivesubjectsexcludedfromthisstudycouldnot
continue this bathing method because of their private matter
which is not a health problem.
3.1. Self-Reported Health Status. Tables  and  show the VAS
scores for self-reported health status every day before and
aer the bathing and showering interventions, respectively.
Signicant improvements were observed for all assessed
items aer each intervention.

Evidence-Based Complementary and Alternative Medicine 
T : Dierences in self-reported health status (VAS score) between bathing and showering interventions.
Bathing Showering Dierence p value
Mean SD Mean SD Mean
Self-reported health . ±. . ±. . .
Skin condition . ±. . ±. . .
Fatigue . ±. . ±. −. . ∗
Stress . ±. . ±. −. . ∗∗
Pain . ±. . ±. −. . ∗
Smile . ±. . ±. . . ∗
∗p<. and ∗∗p<..
T : Health-related quality of life (SF- scores) reported retrospectively for each intervention period.
Bathing Showering Dierence p value
Mean SD Mean SD Mean
General health . ±. . ±. . . ∗∗
Physical functioning . ±. . ±. . .
Role physical . ±. . ±. −. .
Bodily pain . ±. . ±. . .
Vitality . ±. . ±. . .
Social functioning . ±. . ±. . . ∗
Mental health . ±. . ±. . . ∗
Role emotional . ±. . ±. . .
Physical component summary . ±. . ±. . .
Mental component summary . ±. . ±. . . ∗∗
∗p<. and ∗∗p<..
T : Retrospectively assessed mood states during each intervention (POMS scores).
Bathing Showering Dierence p value
Mean SD Mean SD Mean
Tension-Anxiety . ±. . ±. −. . ∗
Depression-Dejection . ±. . ±. −. . ∗
Anger-Hostility . ±. . ±. −. . ∗
Fatigue . ±. . ±. −. .
Confusion . ±. . ±. −. .
Vigor . ±. . ±. . .
∗p<..
Table  shows the results for self-reported health status
during each intervention completed retrospectively aer each
intervention period. VAS scores were higher for self-reported
health and skin condition (p <.) and signicantly higher
for smile (p <.) during bathing intervention than during
showering intervention. In addition, fatigue, stress, and pain
scores were signicantly lower during bathing intervention
than during showering intervention (p <.).
3.2. Health-Related Quality of Life Assessment. Tab l e  s h ows
theindividualscoresfortheitemsontheSF-andthe
Physical and Mental Component Summary scores indicating
health status during each -week intervention, as retro-
spectively self-reported aer completing each intervention.
General health, social functioning, mental health, and Mental
Component Summary scores were signicantly higher dur-
ing bathing intervention than during showering intervention
(p <.). ere were no dierences in role physical,
physical functioning, bodily pain, role emotional, or Mental
Component Summary scores.
3.3. Mood States. Table  shows mood states assessed aer
the -week bathing intervention and the -week showering
intervention, measured using the -item POMS. Scores were
signicantly lower for tension-anxiety, depression-dejection,
and anger-hostility during bathing intervention than during
showering intervention (p <.). ere were no signicant
dierences in fatigue, confusion, or vigor.
4. Discussion
is randomized controlled trial comparing the physical and
mental eects of  weeks of bathing intervention and  weeks
of showering intervention (without immersion) showed that

 Evidence-Based Complementary and Alternative Medicine
bathing intervention was more benecial than showering
intervention.esamplesizeissmall,whichmeansthisresult
haslimitedpower.Howeverthisisacross-overstudy,sothat
we think the result which we showed is a casual relationship.
Self-assessment of health status before and aer inter-
vention every day showed health improvement aer both
bathing and showering interventions, although the degree of
improvement was larger aer the former than aer the latter.
isresultsuggeststhateitherinterventionimprovesphysical
and mental condition. Bodily cleanliness and a feeling of
refreshment are benets oered by bathing and showering.
Bathing intervention did, however, show better subjective
health status (VAS scores) than showering intervention.
Our previous cross-sectional studies [, ] suggested
that people who had a habit of bathing in hot water have good
subjective health status, sucient sleep and rest, low levels of
stress, and high subjective happiness. e results of this study
support that the psychological benets of bathing are a real
causal relationship.
During bathing, several actions unique to bathing will
be exerted on the body, including hyperthermic action,
hydrostatic pressure, buoyancy, and viscosity of water.
e most important of these is hyperthermic action,
which warms the blood in supercial vessels, thereby increas-
ing the deep body temperature through circulation. With
an increase in body temperature, heat-sensitive neurons
areexcitedwhilecold-sensitiveneuronsareinhibitedin
the thermoregulatory center of the hypothalamus, causing
inhibition of the sympathetic nerves and stimulation of
the parasympathetic nerves, leading to vasodilatation and
induced perspiration to decrease the body temperature. Heart
rate will rise by % to %, and peripheral pO2will increase
while pCO2will decrease, thereby stimulating metabolism
and inducing elimination of metabolic waste materials, which
in turn refreshes the body [–]. In terms of hydrostatic
pressure, it induces venous ow, thereby increasing cardiac
outputandimprovingmetabolism.Also,ahabitofimmer-
sionbathinginhotwaterwasshowntobeassociatedwith
strengthened immune function [, ].
A bathing study using patients with cardiovascular dis-
eases showed the improvement of hemodynamics by heating
eect []. On the other hand, for aged generation especially
patients for cardiovascular diseases, full body immersion
wouldbeunbenecialbecausehydrostaticpressurecauses
venous return load.
is study showed better self-assessment results for
fatigue, subjective health, skin condition, and smile as well
as a better SF- Physical Component Summary score during
the intervention with daily immersion bathing, suggesting
systemic improvement of metabolism by taking an immer-
sion bath. Furthermore, hyperthermic action is expected to
systemically relax the muscles, soen collagen in ligaments
and articular capsules, and improve musculoskeletal func-
tion. e pain-relieving eect of bathing [] may explain
the reduction in self-rated pain reported by subjects in the
present study. Lastly, the downward force of gravity is reduced
by buoyancy during bathing, which may in turn lead to
the improvements seen in the POMS constructs of tension-
anxiety, depression-dejection, and anger-hostility, suggesting
positive eects of stress relief, refreshment, and relaxation
from immersion bathing.
e limitations of this study are as follows. is trial
wasconductedinthefall(October-November),andseasonal
dierences in bathing habit (e.g., autumn versus summer
or winter) were not taken into account. Also, the timing of
body immersion and the temperature of water in the bathtub
were not strictly dened. Interventional studies using tightly
controlled conditions will provide insight that is useful for
health promotion. In addition, there may be a bias caused by
the fact that Japanese likes bathing in general. Even though we
think that heating eect of bathing does not dier depending
on races, if we do the same intervention study with people
in Europe, the result may be changed because the favor
regarding bathing may be dierent between Japanese and
people in other countries
5. Conclusions
Routine immersion bathing appeared more benecial to
mental and physical health than routine shower bathing
without immersion. Further interventional studies that con-
sider seasonal factors and physiological factors in relation
to eective bathing temperature and timing are anticipated
to show the eect of immersion bathing and clarify the
benecial eects on health.
Data Availability
edatausedtosupportthendingsofthisstudywere
provided by Japan Health & Research Institute under license
and so cannot be made freely available. Access to these
data will be considered by the author upon request, with
permission of Yasuaki Goto.
Disclosure
A part of this study was presented at st American Public
Health Association Annual Meeting and Exposition .
Conflicts of Interest
e authors have no conicts of interest to declare.
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