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R E V I E W A R T I C L E Open Access
Medical empirical research on forest
bathing (Shinrin-yoku): a systematic review
Ye Wen
1,2
, Qi Yan
1
, Yangliu Pan
1
, Xinren Gu
1*
and Yuanqiu Liu
1*
Abstract
Aims: This study focused on the newest evidence of the relationship between forest environmental exposure and
human health and assessed the health efficacy of forest bathing on the human body as well as the methodological
quality of a single study, aiming to provide scientific guidance for interdisciplinary integration of forestry and
medicine.
Method: Through PubMed, Embase, and Cochrane Library, 210 papers from January 1, 2015, to April 1, 2019, were
retrieved, and the final 28 papers meeting the inclusion criteria were included in the study.
Result: The methodological quality of papers included in the study was assessed quantitatively with the Downs
and Black checklist. The methodological quality of papers using randomized controlled trials is significantly higher
than that of papers using non-randomized controlled trials (p< 0.05). Papers included in the study were analyzed
qualitatively. The results demonstrated that forest bathing activities might have the following merits: remarkably
improving cardiovascular function, hemodynamic indexes, neuroendocrine indexes, metabolic indexes, immunity
and inflammatory indexes, antioxidant indexes, and electrophysiological indexes; significantly enhancing people’s
emotional state, attitude, and feelings towards things, physical and psychological recovery, and adaptive behaviors;
and obvious alleviation of anxiety and depression.
Conclusion: Forest bathing activities may significantly improve people’s physical and psychological health. In the
future, medical empirical studies of forest bathing should reinforce basic studies and interdisciplinary exchange to
enhance the methodological quality of papers while decreasing the risk of bias, thereby raising the grade of paper
evidence.
Keywords: Forest bathing (Shinrin-yoku), Systematic review, Methodology
Introduction
Subhealth is a third state between health and disease.
The most common symptoms of subhealth are fatigue,
poor sleep quality, forgetfulness, physical pain, and sore
throat, and subhealth also increases the risk of infection
and degrades the capacity of the immune system [1,2].
With the rapid development of the global economy and
urbanization, increasing numbers of people have begun
to show subhealth symptoms. In a survey conducted by
the Ministry of Health, Labor and Welfare of Japan (32,
000 Japanese people over 12 years old), 54.2% of respon-
dents considered their stress levels to be “very high”or
“relatively high”[3]. It is estimated that one third of
American adults have nighttime sleep problems every
week, and between 50 and 70 million people complain
that nighttime sleep deprivation is mediated by daytime
impairment [4,5]. A meta-analysis showed that between
one third and one half of the population in the UK was
affected by chronic pain, and the incidence of chronic
pain in different body parts among adult residents was
35.0–51.3%, and the incidence of chronic pain increased
with age [6]. Under the background of the increasing
number of people with subhealth around the world, for-
est bathing (Shinrin-yoku) therapy came about, which
not only brings people with subhealth a healthy lifestyle
advocated by modern medicine but also offers comple-
mentary therapies to the sick [7]. The term forest bath-
ing was created in 1982 by the Ministry of Agriculture,
Forestry and Fisheries of Japan [8]. It refers to a healing
© The Author(s). 2019 Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0
International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and
reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to
the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver
(http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.
* Correspondence: Jiujiuyl@163.com;Liuyq404@163.com
1
College of Forestry, Jiangxi Agricultural University, 1101 ZhiMin Road,
Nanchang 330045, China
Full list of author information is available at the end of the article
Environmental Health and
Preventive Medicin
e
Wen et al. Environmental Health and Preventive Medicine (2019) 24:70
https://doi.org/10.1186/s12199-019-0822-8
technique that restores the physical and psychological
health of the human body through a “five senses experi-
ence”(vision, smell, hearing, touch, and taste) when the
body is exposed to a forest environment. Forest bathing
has positive effects on human physical and mental health
[9,10], especially in enhancing immunity, treating chronic
diseases, regulating mood, and reducing anxiety and de-
pression [11–14]. More benefits can be gained from exer-
cising or meditating in a forest environment than in an
urban environment [15,16]. In recent years, although
medical empirical research on forest bathing has increased
gradually, its healthcare mechanism for the human body
has not been clearly defined due to a lack of research re-
sults, a low level of evidence, and a disciplinary barrier. Al-
though forestry scholars and medical scholars have carried
out relevant research on forest bathing therapy, there are
still some limitations due to different research focuses. (1)
The theoretical basis of research varies. Medical scholars
mainly take evidence-based medicine as the theoretical
basis for studying the physiological and psychological
stress response of the human body during exposure to the
forest environment to demonstrate the health-related ef-
fects of forest bathing. Forestry scholars mainly study the
health mechanism of forest environmental factors and the
relationship among them based on the theory of forestry.
(2) The subject of research varies. The research subject of
medical scholars is the human body, through studying
changes in physiological and psychological indicators to
directly verify the health-related effects of forest bathing.
The research subject of forestry scholars is the forest en-
vironment, through the study of forest environmental fac-
tors of different variables to indirectly prove the health
benefits of forest bathing. To solve this problem, this study
uses the evidence-based medicine system evaluation
method to qualitatively integrate the research results. The
objectives are as follows: (1) focus on the latest evidence
of the relationship between forest environment exposure
and human health, (2) assess the methodological quality
of individual studies, and (3) provide scientific theoretical
guidance for the interdisciplinary integration of forestry
and medicine.
Methods
Selection criteria
(1) Interventional study on the health effects of forest
bathing. (2) Number of intervening measures is less than
or equal to 3. (3) Trial was carried out in a forest envir-
onment. (4) The study period of the paper was from
January 1, 2015, to April 1, 2019. (5) The paper is writ-
ten in English. (6) Subjects are human.
Paper search
Through computer retrieval of PubMed, Embase, and
Cochrane Library, we screened medical empirical research
papers on forest bathing published in the last 5 years, and
used a citation traceability method and Google academic
search for papers that needed to be supplemented. In this
study, the combination of subject words and free words
was adopted, and the logical character “OR”was used to
link each search term to obtain final search results. Search
terms are shown in Table 4 in Appendix.
Paper screening and data extraction
Paper preliminary screening was conducted independently
by one researcher through reviewing titles and abstracts,
and data extraction was conducted independently by two
researchers. After extraction, cross-checking was con-
ducted, and disputes were resolved through discussion or
referring to third-party opinions. Data extraction includes
author name, publication year, study design, participant
profile, ethical review, sample size, intervention measures,
control measures, measurements, and outcomes.
Quality assessment tool
The methodological quality of the included studies was
assessed using the Downs and Black checklist [17], which
was used for quantitative evaluation of the quality of
papers in randomized controlled trials (RCTs) and non-
randomized controlled trials (NRCTs). The evaluation
included 27 items from 5 aspects of the paper: reporting,
external validity, bias, confounding, and power. The evalu-
ation was carried out by two researchers independently,
and any disputes could be resolved through discussion or
by referring to the opinions of a third party. The system
evaluation report was prepared according to the Preferred
Reporting Items for Systematic Reviews and Meta-
Analyses [18] declaration standard.
Results
Search results
Initially, 210 papers were searched, and 17 duplicate pa-
pers and 133 irrelevant papers were removed based on
title and abstract. Subsequently, we evaluated the full
text and excluded 32 papers. Finally, 28 papers met the
criteria for inclusion in the study. The screening process
is shown in Fig. 1.
General characteristics
General characteristics of the included studies are shown
in Table 1. A total of five countries or regions, including
Japan, South Korea, Poland, China, and Taiwan, have
conducted empirical studies on the health effects of
forest bathing [19–46], among which 27 studies were
conducted in Asian countries [19–34,36–46] and 1
study [35] in a European country. Japanese scholars had
the largest number of studies, publishing 13 papers [19,
20,22–25,28,31,38,40,42–44], accounting for 46% of
the total number of included studies, followed by
Wen et al. Environmental Health and Preventive Medicine (2019) 24:70 Page 2 of 21
Chinese, South Korean, Taiwanese, and Polish scholars,
publishing 6 papers [27,32,37,39,45,46], 5 papers [21,
26,29,30,34], 3 papers [33,36,41], and 1 paper [35],
respectively, accounting for 21%, 18%, 11%, and 4% of
the total number of included studies, respectively.
Among them, there were 17 RCTs [20,21,24–27,
30–32,35,37–40,43,45,46], accounting for 61% of
the total number of included studies, and 11 NRCTs
[19,22,23,28,29,33,34,36,41,42,44], accounting
for 39% of the total number of included studies. The
participants were dominated by healthy people, with a
total of 17 studies [20,24,26,29,31,33–38,40,42–46],
accounting for 61% of the total number of studies in-
cluded, and mostly young people aged 18–30. There were
11 studies [19,21–23,25,27,28,30,32,39,41] on people
with health problems, accounting for 39% of the total
number of studies, most of which were middle-aged and
elderly people over 45 years old. There were 13 studies
[19,21,24,29–31,33,34,37,38,40,43,45] with more
than 50 samples, accounting for 46% of the total number
of included studies, 8 studies [20,22,23,25,27,36,41,44]
with less than 20 samples and 7 studies [26,28,32,35,39,
42,46]with20–50 samples, accounting for 29% and 25%
of the total number of included studies, respectively.
There were 20 forest bathing studies [19,20,22–26,28,
31,33,35–38,40,42–46]thatlastedfor1–3days,
accounting for 71% of the total number of included stud-
ies. There were 8 forest bathing studies [21,27,29,30,32,
34,39,41] that lasted for more than 3 days, accounting for
29% of the total number of included studies. Most
scholars have taken ethical considerations into account
when carrying out research. A total of 25 studies [19,20,
22–44] have passed the ethical review, accounting for 89%
of the total included studies. This was not mentioned in 3
studies [21,45,46], accounting for 11% of the total num-
ber of included studies. There were 3 interdisciplinary
studies [44–46], accounting for 11% of the total included
studies.
Intervention measures and control measures
The detailed characteristics of the included research pa-
pers are shown in Tables 2and 3. All studies take forest
or urban environment exposure as the trial premise, and
more than one or two intervention measures are
adopted to carry out the trial, and some control mea-
sures are imposed. The interventions are mostly walking,
meditation, yoga, Pilates, sightseeing, and crafts. The
“five senses experience”and exercise are at the core. The
control measures of each study are similar, mainly in-
cluding the following: (1) control trial time and activity
space; (2) prohibit or control tobacco, alcohol, and caf-
feine intake; (3) prohibit or allow use of drugs and
Fig. 1 Flow diagram of the screening process
Wen et al. Environmental Health and Preventive Medicine (2019) 24:70 Page 3 of 21
electronic products; (4) control of accommodation and
diet; (5) consideration of female physiological period fac-
tors; and (6) increase buffer time (many hours or days)
in a cross-over study to prevent carryover effect.
Evaluative measures
The evaluative measures for the healthcare effect of for-
est bathing are generally divided into self-reported mea-
sures and physiological measures according to different
research purposes for choosing the appropriate evalu-
ative measures, both of which can reflect the psycho-
logical and physiological stress response of the human
body. Self-reported measurement combined with physio-
logical indicators was the largest research method and
used a total of 16 studies [19,20,22,23,25–30,32–34,
36,37,43], accounting for 57% of the total included
studies. There are 6 studies each that only use self-
reported measurement [21,35,40,44–46] or physio-
logical indicator measurement [24,31,38,39,41,42],
each accounting for 21.5% of the total number of in-
cluded studies. Self-reported measurement is widely
used because it is simple to measure and easy to conduct
quantitative analysis. Currently, internationally accepted
self-reported measurement has been applied in the
empirical research of forest bathing. Some scholars also
use a homemade scale for research [45,46]. In physio-
logical measures, due to the limitation of the trial envir-
onment, blood, urine, or saliva samples that require
strict storage time and temperature are generally col-
lected on the spot before and after the forest bathing, or
at a place with good medical conditions according to the
different testing items. Physiological indicators such as
blood pressure, heart rate, pulse, and brain waves are
generally measured by portable instruments.
Physiological response
Cardiovascular function and hemodynamic indexes
There were 8 studies [19,22,28,29,33,36,37,39] in-
volving blood pressure, and systolic blood pressure
(SBP) and diastolic blood pressure were significantly re-
duced in 4 of these studies [19,22,33,37], while only
SBP was significantly decreased in 1 study [24], and only
SBP was significantly increased in 1 study [15]. There
were 4 studies [23,28,33,36] in which pulse was signifi-
cantly decreased. There were 3 studies [20,25,43] in-
volving heart rate, which was significantly decreased in 2
studies [25,43]. There were 7 studies [20,25,29,33,34,
38,43] involving heart rate variability (HRV); the natural
logarithmic value of the high frequency (lnHF) of HRV
was significantly increased in 4 studies [20,25,38,43],
and the natural logarithmic value of the low frequency
(lnLF)/lnHF of HRV was significantly decreased in 2
studies [38,43]. There were 2 studies [32,39] in which
brain natriuretic peptide was significantly decreased.
There was 1 study [32] in which Endothelin-1 was sig-
nificantly decreased.
Neuroendocrine indexes
There were 3 studies [23,27,31] in which cortisol was
significantly decreased. There were 3 studies [22,27,28]
involving adrenaline, which was significantly decreased
in 2 studies [22,27]. There was 1 study [28] involving
norepinephrine and dopamine, which were significantly
decreased.
Metabolism indexes
There were 2 studies [28,29] involving triglycerides,
which were significantly decreased in 1 study [29]. There
was 1 study [28] involving adiponectin, which was sig-
nificantly increased.
Immune and inflammatory indexes
There were 2 studies [27,41] involving nature killer
(NK) cells, which were significantly decreased in 1 study
[27]. There was 1 study [27] involving NKT-like cells,
which were significantly decreased. There was 1 study
[41] involving NK cell activity, which was significantly
increased. There were 4 studies [26,27,32,39] involving
Table 1 General characteristics of included studies (n= 28)
Characteristic Categories No. (%)
Country or region China 6 (21)
Korea 5 (18)
Japan 13 (46)
Poland 1 (4)
Taiwan 3 (11)
Research design RCT 17 (61)
NRCT 11 (39)
Participant Healthy people 17 (61)
People with health problems 11 (39)
Average age (years) 18 ≤1 (3.5)
>18≤30 12 (43)
>30≤45 1 (3.5)
> 45 12 (43)
Age unknown 2 (7)
Sample size ≤20 8 (29)
>20≤50 7 (25)
> 50 13 (46)
Time 3 days ≤20 (71)
> 3 days 8 (29)
Ethical consideration Yes 25 (89)
No 3 (11)
Interdisciplinary research Yes 3 (11)
No 25 (89)
Wen et al. Environmental Health and Preventive Medicine (2019) 24:70 Page 4 of 21
Table 2 Medical empirical research (n= 25)
Authors
(year)
Research design Participants Intervention measures Control measures Measurements and outcomes
Trial group Control group Self-report measures Physiological measures
Horiuchi
(2015) [19]
NRCT
(before-after study) ※
1) Response group: Male
and female participants,
average age was 63.9
years (n= 27). 2) Non-
response group: Male
and female participants,
average age was 61.6
years (n= 27).
N/A Participants were exposed
to forest environment and
the activity was carried
out for 90 min
1) Participants were
divided into 2 groups
according to the changes
of mean arterial pressure
before and after forest
bathing (>5% was the
response group, <5% was
the non-response group).
2) Some participants were
given medications for
hypertension, diabetes,
hyperlipidemia,
hyperuricemia, and
osteoporosis.
3) Smoking and caffeine
were banned 12 h before
the trial, and alcohol was
banned 24 h before the trial
1) Response
group
POMS:
D*↓
V*↑
T-A*↓
F*↓
C*↓
A-H*↓
2) Non-
response
group
POMS:
D*↓
V*↑
T-A*↓
F*↓
C*↓
A-H↓
1) Response group:
SBP*↓
DBP*↓
Mean arterial pressure*↓
Salivary amylase↓
2) Non-response group:
SBP*↓
DBP↓
Mean arterial pressure*↓
Salivary amylase↑
Igarashi
(2015) [20]
RCT
(cross-over study) ※
Female participants,
average age was 46.1
years (n= 4 or 1)
Female
participants,
average age was
46.1 years (n=4
or 1)
After a 3-min rest, the
participants sat and
watched the kiwi orchard
for 10 min (or the building
site); after a 3-min rest, the
participants sat and
watched the building site
(or the kiwi orchard), each
group was asked to view
2 trial sites
1) The trial began in the
summer. 2) Seventeen
participants were divided
into five groups. 3)
Participants avoided
menstruation and did not
drink or smoke. 4) Lived in
the suburbs. 5) The two trial
sites are close to each other
SD method:
Comfortable
feeling
#
↑
Natural feeling
#
↑
Relaxed feeling
#
↑
POMS:
D
#
↓
V
#
↑
T-A
#
↓
F
#
↓
C
#
↓
A-H
#
↓
lnHF #↑
lnLF/lnHF↓
Heart rate↓
Kang
(2015) [21]
RCT Male and female
participants, average age
was 54.8 years (n=32)
Male and female
participants,
average age was
50 years (n=32)
In the morning, the trial
group and control group
were exposed to the
forest environment and
walked for 2 h In the
afternoon, the trial group
performed additional
stretching and intensive
exercises for 4 h
1) The trial began in late
spring and lasted five days.
2) Participants selection
criteria: Adults over 20 years
of age with posterior neck
pain for more than 3
months, and VAS grades
over 4
VAS:
VAS on the first
day*↓
VAS on the end
day*↓
Cervical range
of motion*↑
Neck disability
index*↓
EuroQol 5D-3 L
VAS*↑
EuroQol 5D-3 L
index*↑
McGill pain
questionnaire*↓
Trigger points in
the posterior
N/A
Wen et al. Environmental Health and Preventive Medicine (2019) 24:70 Page 5 of 21
Table 2 Medical empirical research (n= 25) (Continued)
Authors
(year)
Research design Participants Intervention measures Control measures Measurements and outcomes
Trial group Control group Self-report measures Physiological measures
neck region
#
↓
Ochiai
(2015a)
[22]
NRCT
(before-after study) ※
Male participants with
high normal blood
pressure, age range 40–
72 years (n=9)
N/A On trial day, participants
were exposed to forest
environment for activities
and rest from 10:30 to
15:05
1) The trial was carried out
in early autumn, and the
average air temperature was
21.5 °C. 2) No alcohol or
conversation was allowed
during the trial, and cell
phones were allowed only
during breaks
SD method:
Comfortable
feeling↑
Natural feeling*↑
Relaxed feeling*↑
POMS:
D↓
V↓
T-A*↓
F↓
C*↓
A-H*↓
POMS total
mood disturbance*↓
SBP*↓
DBP*↓
Urinary adrenaline levels
*↓
Serum cortisol levels *↓
Ochiai
(2015b)
[23]
NRCT
(before-after study) ※
Female participants, the
average age was 62.2 years
(n= 17)
N/A On trial day, participants
were exposed to forest
environment for activities
and rest from 10:32 to
15:13
1) The trial was carried out
in summer, and the average
air temperature was 21.5 °C.
2) Except for 6 participants
who were taking
medication to control their
blood pressure, the rest of
the participants had no
other physical or
psychological diseases. 3)
No alcohol or cell phones
were allowed during the
trial
SD method:
Comfortable
feeling*↑
Natural feeling*↑
Relaxed feeling*↑
POMS:
T-A*↓
F↓
V*↑
Pulse rate*↓
Salivary cortisol
concentration *↓
Song
(2015a)
[24]
RCT
(cross-over study) ※
Male participants, the
average age was 21.5
years (n=6)
Male participants,
the average age
was 21.5 years(n=
6)
Day 1, the trial group was
exposed to forest
environment and walked
for 15 min, while the
control group was
exposed to urban
environment and walked
for 15 min. Day 2, the two
groups interchanged
environments
1) The trial lasted for 2 days.
2) Smoking and drinking are
prohibited during the trial.
3) The trial was conducted
several times and a total of
92 participants participated
N/A If the participants had high
initial blood pressure and
pulse, forest walking could
reduce these two
indicators. The results were
reversed if the participants
had lower initial blood
pressure and pulse
Song
(2015b)
[25]
RCT
(cross-over study) ※
Male participants with
hypertension or high
normal blood pressure,
the average age was 58
years (n= 10)
Male participants
with hypertension
or high normal
blood pressure,
the average age
was 58 years(n=
10)
Day 1, the trial group was
exposed to forest
environment and walked
for 17 min, while the
control group was
exposed to urban
environment and walked
for 17 min. Day 2, the two
groups interchanged
1) The trial lasted for 2 days.
2) When the trial was
carried out, the average air
temperature in the forest
was 21.4 °C, and that in the
city was 28.1 °C. 3) Smoking,
alcohol and caffeine
consumption were
prohibited during the trial.
SD method:
Comfortable feeling
#
↑
Natural feeling
#
↑
Relaxed feeling
#
↑
POMS:
D
#
↓
V
#
↑
T-A
#
↓
F
#
↓
lnHF
#
↑
Pulse rate
#
↓
Wen et al. Environmental Health and Preventive Medicine (2019) 24:70 Page 6 of 21
Table 2 Medical empirical research (n= 25) (Continued)
Authors
(year)
Research design Participants Intervention measures Control measures Measurements and outcomes
Trial group Control group Self-report measures Physiological measures
environments 4) Participants who were on
medication were excluded.
5) Trial at the same time
every day
C
#
↓
A-H
#
↓
Im
(2016) [26]
RCT
(cross-over study) ※+
Male and female
participants, age range
18–35 years (n= 19)
Male and female
participants, the
age range 18–35
years(n=22)
In the morning, the trial
group was exposed to
forest environment for 2 h,
while the control group was
exposed to urban
environment for 2 h. In the
afternoon, the two groups
interchanged environments
1) The trial began in the
summer. 2) The participants
had no mental illness, allergic
rhinitis or bronchitis. 3)
Bachelor’s degree or above
and live in city. 4) To avoid
carryover effect, the interval
between morning trial and
afternoon trial was 2 h.
5) Alcohol consumption was
restricted 12 h before the
test, and food consumption
was restricted 1 h before the
test. Smoking and drinking
were prohibited during the
test, and electronic products
were restricted.
6) All groups had the same
diet
Stress response
inventory:
Total
#
↓
Somatic
symptoms
#
↓
Depressive s
ymptoms
#
↓
Anger symptoms↓
IL-6↑
IL-8
#
↓
TNF-α
#
↓
GPx
#
↑
Jia
(2016) [27]
RCT※Male and female
participants with COPD
(n= 10)
Male and female
participants with
COPD (n=8)
In the morning, the trial
group was exposed to
forest environment and
walked for 90 min, while
the control group was
exposed to urban
environment and walked
for 90 min. Afternoon is
the same as morning
1) The trial began in the
summer. 2) The participants
did not have acute
exacerbation. 3) Participants
have the same
accommodation and
schedule. 4) The trial lasted
for 4 days
POMS:
D*↓
V↑
T-A*
#
↓
F↓
C↓
A-H*↓
NK cells *↓
CD8+ T-lymphocytes
expressing perforin *
#
↓
NKT-like cells *
#
↓
IL-6*
#
↓
IL-8*
#
↓
Interferon-γ*
#
↓
TNF-α↓
IL-1β
#
↓
CRP
#
↓
Pulmonary and activation-
regulated chemokine*
#
↓
Tissue inhibitor of
metalloproteinase-1*
#
↓
Surfactant protein D
#
↓
Cortisol
#
↓
Epinephrine*
#
↓
Li
(2016) [28]
NRCT※Male participants with
hypertension or high
normal blood pressure,
age range 40–69 years
(n= 19)
Male participants
with hypertension
or high normal
blood pressure,
age range 40–69
years (n= 19)
In the first trial, the control
group was exposed to
urban environment and
walked 2.6 km. In the
second trial, the control
group was exposed to
forest environment and
1) The trial began in the
summer. 2) Participants did
not take any
antihypertensive drugs. 3)
No alcohol was allowed and
the diet was the same
during the trial. 4) The
POMS:
D
#
↓
V
#
↑
T-A
#
↓
F
#
↓
C
#
↓
A-H!
SBP!
DBP!
Pulse rate
#
↓
Triglycerides!
Cho!
LDL-Cho!
HDL-Cho!
Wen et al. Environmental Health and Preventive Medicine (2019) 24:70 Page 7 of 21
Table 2 Medical empirical research (n= 25) (Continued)
Authors
(year)
Research design Participants Intervention measures Control measures Measurements and outcomes
Trial group Control group Self-report measures Physiological measures
walked 2.6 km interval between the two
trials was one week
Remnant-like particles Cho!
Adiponectin
#
↑
Glycated hemoglobin!
Blood glucose!
Insulin!
Dehydroepiandrosterone
sulfate!
CRP!
Epinephrine↓
Norepinephrine *
#
↓
Dopamine
#
↓
Bang
(2017) [29]
NRCT※Male and female
participants, the average
age was 24.8 years
(n= 51)
Male and female
participants, the
average age was
23.8 years (n= 48)
The participants walked in
the campus forest once a
week for 40 min
1) The trial began in the
autumn. 2) The trial lasted
for 6 weeks. 3) The trial
group received extra
messages of
encouragement during the
trial and attended a stress
management seminar
Health-promoting
Lifestyle profile II:
Total
#
↑
Responsibility for
health
#
↑
Physical activity↑
Healthy nutrition↑
Social relations↑
Stress management
#
↑
Spiritual growth↑
BDI score
#
↓
SBP #↑
DBP↑
Cho↓
HDL-Cho↓
LDL-Cho↑
Triglycerides
#
↓
Bone density
#
↑
Body Mass Index↑
Percent of body fat↑
lnLF/lnHF↑
Parasympathetic nerve
activity↑
Chun
(2017) [30]
RCT※+ Male and female
participants with chronic
stroke, the average age
was 60.8 years (n=30)
Male and female
participants with
chronic stroke, the
average age was
60.8 years (n= 29)
The trial group was
exposed to forest
environment for
meditation and walking.
The control group was
exposed to urban
environment for
meditating and walking
2) The trial lasted for 4 days BDI score*
#
↓
Score of 17-item
version of the
Hamilton Depression
Rating Scale*
#
↓
STAI score*
#
↓
Reactive oxygen
metabolites↓
Biological antioxidant
potential*
#
↑
Kobayashi
(2017) [31]
RCT
(cross-over study)※
Male participants, the
average age was 21.7
years (n= 12)
Male participants,
the average age
was 21.7 years (n
=12)
Day 1, the trial group was
exposed to forest
environment, while the
control group was
exposed to urban
environment. Day 2, the
two groups interchanged
environments
1) The trial began in the
summer and early autumn.
2) The trial lasted for 2 days.
3) 34 forests and cities were
selected for the trial, and a
total of 34 trials were carried
out
N/A Salivary cortisol
concentration
#
↓
Mao
(2017)
[32]
RCT※Male and female
participants with chronic
heart failure, age range
65–80 years (n= 23)
Male and female
participants with
chronic heart
failure, age range
65–80 years (n=
10)
The trial group and
control group were
exposed to forest and
urban environment,
respectively, and walked
for 1.5 h in the morning
and afternoon
1) The trial began in the
summer. 2) The trial lasted
for 5 days. 3) All groups had
the same diet. 4) Smoking,
drinking alcohol and
caffeinated beverages were
prohibited during the trial.
5) Medication taken
POMS:
D*
#
↓
V↓
T-A
#
↓
F↓
C*↓
A-H*↓
BNP*
#
↓
N-terminal pro-BNP!
Endothelin-1
#
↓
ANGII↓
ANGII receptor type 1↑
ANGII receptor type 2 *↑
Angiotensinogen↓
IL-6
#
↓
Wen et al. Environmental Health and Preventive Medicine (2019) 24:70 Page 8 of 21
Table 2 Medical empirical research (n= 25) (Continued)
Authors
(year)
Research design Participants Intervention measures Control measures Measurements and outcomes
Trial group Control group Self-report measures Physiological measures
normally during the trial TNF-α↓
CRP↓
Total superoxide
dismutase
#
↑
Malondialdehyde
#
↓
Yu
(2017)
[33]
NRCT
(before-after study)※
Male and female
participants, age range
45–86 years (n= 128)
N/A participants were recruited
at the gate of the forest
park to conduct a 2-h
forest tour and walk a
total of 2.5 km
1) The trial began in the
summer. 2) Smoking,
drinking alcohol and
caffeinated beverages were
prohibited during the trial
POMS:
D*↓
V*↑
T-A*↓
F*↓
C*↓
A-H*↓
STAI score*↓
Pulse rate *↓
SBP *↓
DBP*↓
lnHF↓
lnLF/lnHF↑
Bang
(2018) [34]
NRCT
(before-after study)※
Elementary school
students, the average
age was 11.83 years
(n= 24)
Elementary school
students, the
average age was
11.75 years (n=
28)
The trial group allocated
30 min for the lecture and
60 min for the forest
activities, while the control
group took only indoor
classes
1) The trial began in the
summer. 2) Once a week for
10 weeks. 3) Children with
medical treatment and
contraindications to exercise
were excluded
1) Trial group
Health status
questionnaire:
Perceived health
status↑
Rosenberg Self-
Esteem Scale:
Self-esteem*↑
Children’s
Depression Inventory:
D*↓
Peer relationship
instrument:
Peer relationships↓
Conners-Wells
Adolescents Self-
Report
Scales:
Attention deficit
and hyperactivity↑
2) Control group
Health status
questionnaire:
Perceived health
status↑
Rosenberg Self-
Esteem Scale:
Self-esteem↓
Children’s Depression
Inventory:
D↓
Peer relationship
instrument:
Peer relationships↑
Conners–Wells
1) Trial group
lnLF/lnHF↑
2) Control group
lnLF/lnHF↓
Wen et al. Environmental Health and Preventive Medicine (2019) 24:70 Page 9 of 21
Table 2 Medical empirical research (n= 25) (Continued)
Authors
(year)
Research design Participants Intervention measures Control measures Measurements and outcomes
Trial group Control group Self-report measures Physiological measures
Adolescents Self-Report
Scales:
Attention deficit
and hyperactivity↓
Bielinis
(2018) [35]
RCT※Male (n= 18) and
female (n= 13)
participants, the average
age was 21.45 years
Male (n= 18) and
female (n=13)
participants, the
average age was
21.45 years
The trial group was
exposed to the forest
environment (deciduous
broad-leaved forest) and
watched the scenery for
15 min, while the control
group was exposed to the
urban environment and
watched the scenery for
15 min
1) The trial began in the
winter. 2) No talking with
each other during the trial
Positive and
negative affect
schedule:
Positive*
#
↑
Negative
#
↓
POMS:
D
#
↓
V*
#
↑
T-A
#
↓
F*
#
↓
C
#
↓
A-H
#
↓
Restorative
Outcome Scale
scores*
#
↑
Subjective Vitality
Scale scores*
#
↑
N/A
Chen
(2018) [36]
NRCT
(before-after study)※
Female participants, age
range 36–62 years
(n= 16)
N/A Day 1, participants were
exposed to forest
environments for walking.
Day 2, participants were
exposed to forest
environments and made
handicrafts
1) The average air
temperature during the trial
was 13.8 °C. 2) participants
had the same
accommodation and diet. 3)
Smoking and stimulant
foods were prohibited
during the trial
POMS:
D↓
V*↑
T-A*↓
F*↓
C*↓
A-H*↓
STAI scores*↓
Pulse rate↓
SBP*↓
DBP↓
Salivary α-amylase↓
Hassan
(2018) [37]
RCT
(cross-over study) ※
Male and female
participants, age range
19–24 years (n= 30)
Male and female
participants, age
range 19–24 years
(n= 30)
Day 1, the trial group was
exposed to forest
environment and walked
for 15 min, while the
control group was
exposed to urban
environment and walked
for 15 min. Day 2, the two
groups interchanged
environments
1) The average air
temperature on the first day
was 22 °C, and the average
air temperature on the
second day was 27 °C. 2)
The trial lasted for 2 days. 3)
Participants had the same
accommodation and diet
STAI scores
#
↓
SD method:
Comfortable feeling
#
↑
Natural feeling
#
↑
Relaxed feeling
#
↑
SBP
#
↓
DBP
#
↓
High alpha brain waves
#
↑
High beta brain waves
#
↑
Relaxation scores
#
↑
Attention scores
#
↑
Kobayashi
(2018) [38]
RCT
(cross-over study) ※
Male and female
participants, age range
19–29 years (n= N/A)
Male and female
participants, age
range 19–29 years
(n= N/A)
Day 1, the trial group was
exposed to forest
environment and walked
for 15 min, while the
control group was
exposed to urban
environment and walked
for 15 min. Day 2, the two
1) The trial was carried out
in 57 cities and forest areas.
2) The trial lasted for 2 days.
3) The total number of
participants was 684, and
the numbers of participants
from trial group or control
group were different in every
N/A lnHF
#
↑
lnLF/lnHF
#
↓
Wen et al. Environmental Health and Preventive Medicine (2019) 24:70 Page 10 of 21
Table 2 Medical empirical research (n= 25) (Continued)
Authors
(year)
Research design Participants Intervention measures Control measures Measurements and outcomes
Trial group Control group Self-report measures Physiological measures
groups interchanged
environments
trial
Mao
(2018)
[39]
RCT※First trial, male and
female participants with
chronic heart failure
(n= 23).
Second trial, male and
female participants with
chronic heart failure
(n= 10)
Male and female
participants with
chronic heart
failure (n=10)
The trial group was
exposed to forest
environment, while
the control group was
exposed to urban
environment
1) The trial was carried out
twice, the first time in late
summer for 5 days, and the
second time in early autumn
for 5 days. 2) No alcohol or
tea was allowed during the
trial
N/A BNP*
#
↓
IL-6!
TNF-α*
#
↓
Total superoxide
dismutase!
Malondialdehyde
#
↓
SBP↓
DBP↓
Song
(2018) [40]
RCT
(cross-over study) ※
Male participants,
average age was 21.7
years (n=6)
Male participants,
the average age
was 21.7 years (n
=6)
Day 1, the trial group was
exposed to forest
environment, while the
control group was
exposed to urban
environment. Day 2,
the two groups
interchanged environments
1) The trial was conducted
in the summer from 2005 to
2013 and lasted for 2 days
at a time. 2) The study was
conducted in 52 urban and
forest areas with a total of
585 participants. 3) Smoking
and drinking alcohol were
prohibited, and limited
caffeine intake
POMS:
D
#
↓
V
#
↑
T-A
#
↓
F
#
↓
C
#
↓
A-H
#
↓
N/A
Tsao
(2018) [41]
NRCT
(before-after study)※
Male and female
participants, the average
age was 60.4 years
(n= 11)
N/A Participants were exposed
to forest environment and
walked 1.5 h in the
morning and afternoon
(in two different forests)
1) The trial began in the
winter. 2) The trial lasted for
5 days. 3) The participants
had no diabetes,
cardiovascular disease or
other major diseases. 4) Diet
control began 10 days
before the trial
N/A NK cells↑
NK cells activity*↑
Wang
(2018) [42]
NRCT
(before-after study) ※
Male and female college
students (n= 22)
N/A The participants carried
out a 2 to 3-day forest trip
1) The trial was conducted
in the fall of 2015, 2016 and
2017. 2) Participants had the
same diet. 3) Smoking,
coffee and tea were not
allowed during the trial
N/A 1) Day after the trial:
Urinary hydrogen
peroxide*↓
Urinary 8-hydroxy-
2’deoxyguanosine*↓
2) One week after the test:
Urinary hydrogen
peroxide*↓
Urinary↓
8-hydroxy-
2’deoxyguanosine*↓
Song
(2019) [43]
RCT
(cross-over study) ※
Female participants, the
average age was 21
years (n=6)
Female
participants, the
average age was
21 years (n=6)
The participants walked in
urban or forest
environment for 15 min
(about 1 km)
1) The trial was conducted
in late summer and early
autumn of 2014, 2015 and
2017. 2) The trial was
conducted in 6 different
urban and forest
environments with a total of
POMS:
D
#
↓
V
#
↑
T-A
#
↓
F
#
↓
C
#
↓
A-H
#
↓
lnHF
#
↑
lnLF/lnHF
#
↓
Heart rate
#
↓
Wen et al. Environmental Health and Preventive Medicine (2019) 24:70 Page 11 of 21
Table 2 Medical empirical research (n= 25) (Continued)
Authors
(year)
Research design Participants Intervention measures Control measures Measurements and outcomes
Trial group Control group Self-report measures Physiological measures
72 participants. 3) Smoking,
drinking alcohol was
prohibited, and limited
caffeine intake
SD method:
Comfortable feeling
#
↑
Natural feeling
#
↑
Relaxed feeling
#
↑
*Significant intra-group differences
#
Significant inter-group differences
n, sample size; “↑”, indicators rise; “↓”, indicators decline; “!”, irregular index; N/A, no report; “※”, has passed ethical review; “+”, illustrates the grouping method; ANGII, Angiotensin II; A-H, anger and hostility; BDI, Beck
depression inventory; BNP, Brain natriuretic peptide; C, confusion; Cho, total cholesterol; COPD, chronic obstructive pulmonary disease; CRP, C-reactive protein; D, depression; DBP, diastolic blood pressure; F, fatigue;
HRV, heart rate variability; HDL, High density lipoprotein; IL, Interleukin; LDL, low density lipoprotein; lnHF, the natural logarithmic value of the high frequency of heart rate variability; lnLF, the natural logarithmic value
of the low frequency of heart rate variability; NK, Nature killer; NKT, Nature killer T; NRCT, non-randomized controlled trial; POMS, profile of mood states; RCT, randomized controlled trial; SBP, systolic blood pressure; SD,
semantic differential; STAI, state-trait anxiety inventory; T-A, tension and anxiety; TNF-α, tumor necrosis factor-α;V, vigor; VAS, visual analog scale
Wen et al. Environmental Health and Preventive Medicine (2019) 24:70 Page 12 of 21
Table 3 Interdisciplinary research (n=3)
Authors
(year)
Research design Participants Intervention
measures
Control
measures
Measurements Outcomes
Trial group Control
group
Self-report
measures
Physiological
measures
Forest inventory
Takayama
(2017) [44]
NRCT
(cross-over study)※
1) Male and
female
participants,
the average
age was
40.2 years
(n= 9).
2) Sparse
forest
environment
1) Male and
female
participants,
the average
age was
40.2 years
(n= 9). 2)
Dense forest
environment
The trial group
was exposed
to a sparse
forest
environment
and sat quietly
for 15 min,
while the
control group
was exposed
to a dense
forest
environment
and sat quietly
for 15 min, and
then the two
groups
exchanged
environments
1) The trial
began in the
summer. 2) The
trial lasted for
4 days. 3)
Alcohol was
banned 24 h
before the trial
and caffeine
was banned
12 h before the
trial. 4) All
subjects did
not have a
history of
cardiovascular
disease and
psychosis, and
did not take
medications
that could
affect their
psychology. 5)
The interval
between the
trial in different
environments
was 10 min
Positive and
Negative Affect
Schedule:
Positive↑
Negative *↓
POMS:
D
#
*↓
V↑
T-A↓
F↓
C↓
A-H↓
Perceived
Restorativeness
Scale:
Compatibility
scores
#
↑
Restorative
Outcome Scale
scores↑
N/A Stand density
Stand basal area
Species
composition
Forest photos
Hemispherical
photograph
Forest
micrometeorology
Temperature↑
Relative
humidity
#
↑
Wind
velocity
#
↓
Radiant heat↑
Illuminance
#
↑
Sound
pressure
#
↑
1) Both sparse
forest and dense
forest had
recovery effect on
the participants,
but the
participants
evaluated the
sparse forest
environment
more positively. 2)
Strengthening
forest structure
management can
improve the
healing effect of
forest
environment on
human body
Guan
(2017) [45]
RCT 1) Male and female
participants, the average
age was 22 years (n=20).
The environment is birch
forest (Betulaplatyphylla
Suk).
2) Male and female
participants, the
average age was
21.6 years (n= 23).
The environment is
maple forest
(Acer triflorum)
3) Male and female
participants, the
average age was
21.6 years (n= 26).
The environment is
oak forest
The
participants
were exposed
to the forest
environment,
first taking a
tree-measuring
course for
20 min, and
then enjoying
40 min of
private time
1) The trial
began in the
spring. 2) All
participants
had no history
of
cardiovascular
disease, allergic
symptoms, or
mental illness.
3) High-
intensity activ
ities, smoking
and drinking
were prohib
ited during the
trial
Homemade
scales:
Anxiety caused
by employment
pressure (birch
forest)*↓
Anxiety caused
by study interest
(maple forest)*↓
Anxiety caused
by lesion
satisfaction
(oak forest)
#
↓
N/A Height of tree
Diameter at
breast height
Canopy length
Canopy cover
rate
Density
1) The correlation of weight, age
and anti-anxiety score was the highest.
2) Forest bathing can
promote college students' inter
est in learning. 3) Overweight
young people were better at re
ducing anxiety. 4) Female partici
pants in the oak forest showed
higher levels of anxiety relief than
male
Wen et al. Environmental Health and Preventive Medicine (2019) 24:70 Page 13 of 21
Table 3 Interdisciplinary research (n=3)(Continued)
Authors
(year)
Research design Participants Intervention
measures
Control
measures
Measurements Outcomes
Trial group Control
group
Self-report
measures
Physiological
measures
Forest inventory
(Quercus mongolica)
Zhou
(2019) [46]
RCT
(cross-over study)
Male and
female
participants,
age range
19–23 years
(n= 24)
Male and female
participants, age
range 19–23 years
(n= 19)
Day 1, the trial
group was
exposed to
urban forest
park, while the
control group
was exposed
to suburban
forest parks.
Day 2, the two
groups
interchanged
environments
1) The trial
began in the
winter. 2) The
trial lasted for
2 days
Homemade
scales
(anti-anxiety score):
Finance state*↑
Exam-pass
pressure*
#
↓
Campus life*
#
↓
Love affair
relationship*↑
N/A Canopy density
Diameter at
breast height
Plant species
1) The forest richness of suburban
forest park is higher than that of
urban forest park. 2) Suburban
forest park can alleviate
interpersonal anxiety in
participants more than urban
forest parks
*Significant intra-group differences
#
Significant inter-group differences
n, sample size; “↑”, indicators rise; “↓”, Indicators decline; N/A, no report; “※”, has passed ethical review; A-H, anger and hostility; C, confusion; D, depression; F, fatigue; NRCT, non-randomized controlled trial; POMS,
profile of mood states; RCT, randomized controlled trial; T-A, tension and anxiety; V, vigor
Wen et al. Environmental Health and Preventive Medicine (2019) 24:70 Page 14 of 21
Interleukin (IL)-6, which was significantly decreased in 2
studies [27,32]. There were 2 studies [26,27] involving
IL-8, which was significantly decreased. There were 3
studies [26,32,39] involving tumor necrosis factor-
alpha, which was significantly decreased in 2 studies [26,
39]. There were 3 studies [27,28,32] involving C-
reactive protein, which was significantly decreased in 1
study [27]. There was 1 study [27] involving IL-1β,
Interferon-γ, pulmonary and activation-regulated che-
mokine, tissue inhibitor of metalloproteinase-1 and sur-
factant protein D, which were all significantly decreased.
Antioxidant indexes
There was 1 study [26] involving glutathione peroxidase,
which was significantly increased. There was 1 study
[30] involving biological antioxidant potential, which
was significantly increased. There was 1 study [42] in-
volving 8-hydroxy-2′deoxyguanosine and hydrogen per-
oxide, which were significantly decreased. There were 2
studies [32,39] involving total superoxide dismutase,
which was significantly increased in 1 study [32]. There
were 2 studies [32,39] involving malondialdehyde, which
was significantly decreased.
Electrophysiological indexes
There was 1 study [37] involving electroencephalogram,
high alpha brain waves and high beta brain waves, which
were significantly increased, and the degree of relaxation
of the human body was significantly increased.
Psychological outcomes
Emotional states
There were 14 studies [19,20,22,23,25,27,28,32,33,
35,36,40,43,44] involving the emotional states of
humans. Among them, “depression,”“tension-anxiety,”
“fatigue,”“confusion,”and “anger-hostility”scores were
significantly decreased in 11 studies [19,20,25,27,28,
32,33,35,40,43,44], 13 studies [19,20,22,23,25,27,
28,32,33,35,36,40,43], 9 studies [19,20,25,28,33,
35,36,40,43], 11 studies [19,20,22,25,28,32,33,35,
36,40,43], and 11 studies [19,20,22,25,27,32,33,35,
36,40,43] respectively. There were 10 studies [19,20,
23,25,28,33,35,36,40,43] in which the “vigor”score
was significantly increased. In addition, 2 studies [35,44]
showed that forest bathing significantly increased posi-
tive emotions and decreased negative emotions.
Attitudes and feelings towards things
There were 6 studies [20,22,23,25,37,43] involving
people’s attitudes and feelings towards things; “comfort-
able,”“relaxed,”and “natural”scores were significantly
increased in 5 studies [20,23,25,37,43], 6 studies [20,
22,23,25,37,43], and 6 studies [20,22,23,25,37,43],
respectively.
Levels of anxiety and depression
There were 6 studies [30,33,36,37,45,46] in which
levels of anxiety were significantly decreased. There were
3 studies [29,30,34] in which levels of depression were
significantly decreased.
Degree of physical and psychological recovery
There were 2 studies [21,26] involving the degree of
physical recovery, in which somatic symptoms were sig-
nificantly decreased. There were 2 studies [35,44]in
which the degree of psychological recovery and mental
health were significantly increased.
Adaptive behavior
There were 2 studies [29,34] involving adaptive behavior,
and the “self-esteem”score was significantly increased in 1
study [34], and the “health promoting behavior”score was
significantly increased in 1 study [29].
Comprehensive study
The study of the comprehensive health care effect of
forest bathing on the human body is still at the primary
stage, and the health care mechanism has not been fully
proved. It is general practice to assume that forest bath-
ing has positive effects on the physical or psychological
health of a certain group of people (such as cardiovascu-
lar disease patients, chronic obstructive pulmonary
disease patients, the subhealth population, etc.) and to
verify whether this hypothesis is valid. The autonomic
nervous system that plays a mediating role in the stress
response of various systems has attracted the attention
of researchers. Based on the data of the 28 papers
included in this study, the lnHF of HRV can reflect
parasympathetic activity, and the lnLF/lnHF of HRV,
urinary adrenalin and norepinephrine can reflect
sympathetic activity [22,38]. When participants were ex-
posed to walking in the forest environment, the cerebral
cortex was in a relaxed state, parasympathetic activity
increased (lnHF increased), and sympathetic activity
decreased (lnLF/lnHF, urinary adrenalin and norepin-
ephrine decreased) [20,25]. Cardiovascular function and
hemodynamic index, neuroendocrine index, metabolism
index, immune and inflammatory index, antioxidation
index, and electrical physiological indexes of the human
body, emotional state, attitudes and feelings towards
things, physiological and psychological recovery degree,
and adaptive behavior of the human body were signifi-
cantly improved. Levels of anxiety and depression were
significantly decreased. Song et al. [24] found that high
initial values in parameters such as blood pressure and
pulse rate in participants were decreased after walking in
the forest environment, while participants with lower
initial values had the opposite effect. Participants who
walked in urban environments did not experience this
Wen et al. Environmental Health and Preventive Medicine (2019) 24:70 Page 15 of 21
phenomenon. This indicates that the physiological effect
will vary depending on the initial value of the partici-
pant, and the forest has a physiological regulation effect
close to the appropriate level of the human body, which
is not completely caused by the exercise itself. Horiuchi
et al. [19] also indicated that the healing effect of forest
bathing has nothing to do with the energy expenditure
during walking. The health benefits of forest bathing are
shown in Fig. 2.
Quality assessment
For methodological quality assessment of papers based
on the Downs and Black checklist, of the 28 papers in-
cluded in the study, 16 [21,24,26,27,29–32,34,35,38,
39,41,44–46] were of high quality and 12 [19,20,22,
23,25,28,33,36,37,40,42,43] were of low quality
(Fig. 3). Among the 16 high-quality papers, there were
12 [21,24,26,27,30–32,35,38,39,45,46] with RCT
and 4 [29,34,41,44] with NRCT. The methodological
quality of papers using RCT is significantly higher than
that of papers using NRCT (p< 0.05) (Fig. 4). On the
whole, the quality of papers designed with RCT was
higher than those with NRCT. In terms of the gener-
ation of random sequences, only 1 paper [30] used
computer-generated random codes with a low risk of
bias. None of the following was mentioned or carried
out in the papers: (1) return visit; (2) blind method for
intervention practitioners, participants, or data analysts;
(3) explain the compliance with the intervention or con-
trol measures; and (4) participants who were lost to
follow-up were included in the study or carried out the
intention-to-treat analysis.
Discussion
Studies on the health effects of forest environment ex-
posure on the human body are gradually increasing.
Currently, there are two main mainstream models. One
is the forest bathing model, which advocates subhealthy
people and sick people going into the forest for activities
which generate a healing effect through forest environ-
mental factors. Forest bathing can regulate blood pres-
sure, reduce blood glucose, regulate endocrine activity,
relieve mental disorders, fight cancer, boost immunity,
and treat respiratory diseases [3,47–52]. In recent years,
increasing numbers of forest bathing trial studies have
been conducted on people with chronic diseases, such as
patients with hypertension or high-normal blood pres-
sure [22,25,28,30,53], chronic obstructive pulmonary
disease patients [27], chronic heart failure [32,39], and
chronic stroke [30]. The second is horticultural therapy,
which guides sick people into the natural environment
and relieves diseases caused mainly by mental stress
Fig. 2 Health benefits of forest bathing
Wen et al. Environmental Health and Preventive Medicine (2019) 24:70 Page 16 of 21
(excessive tension, panic, insomnia, etc.) through com-
munication with people, making crafts, and gardening
activities. Others include pain and sports injuries such as
mild hemiplegia, lower body paralysis, and cognitive im-
pairments such as speech disorders, spatial identification
disorders, memory disorders, attention disorders, and
illogicality [54,55]. The similarities between forest bath-
ing and horticultural therapy are as follows: (1) They are
complementary therapies and cannot replace drugs. (2)
They are a healing method to restore the health of the
human body through the “five senses experience.”The
difference between forest bathing and horticultural ther-
apy are as follows: (1) Their medical categories are
different. Forest bathing belongs to the category of pre-
ventive medicine, which is mainly aimed at subhealthy
people, and the prevention of diseases is its main pur-
pose. Horticultural therapy belongs to the category of re-
habilitation medicine, which is mainly aimed at
eliminating and reducing dysfunction of the human
body, and making up and rebuilding the function of the
human body is its main purpose. (2) Their core content
is different. The main content of forest bathing is to ex-
ercise or meditate in the forest environment, using the
forest environmental factors to promote human physical
and psychological health. Horticultural therapy is more
focused on hand-brain coordination, emphasizing con-
tact with natural things and gaining satisfaction through
work. In view of this, different populations should
choose appropriate healthcare models. Some scholars
[36] combined the 2 healthcare models and achieved
very good results.
Based on the data of the 28 papers included in this
study, forest bathing has a significant role in promoting
human physiology and mental health. Past methods
using physiological and self-report measures to distin-
guish between physiological and psychological research
are no longer feasible. The boundaries between the two
Fig. 3 Quality appraisal of included studies using a Downs and Black checklist
Fig. 4 Score of RCT (n= 17) and NRCT (n= 11), means ± SD, *p<
0.05, one-way analysis of variance (ANOVA)
Wen et al. Environmental Health and Preventive Medicine (2019) 24:70 Page 17 of 21
are becoming increasingly blurred. The mainstream re-
search method in the future will be systematic study of
physiological measures combined with self-report mea-
sures. For example, in the study of the recovery of phys-
ical symptoms or the relief of physiological pain, health
effects can be shown by physiological indicators, but
self-report measures (such as visual analog scale [21],
stress response inventory [26], etc.) can also be used for
evidence. Research on the regulation of the human emo-
tional state can use self-reported measures for proof,
and physiological measures can also be used for evidence
(such as HRV [25,33,38], brain wave activity [37], and
skin electricity [53]). Although the forest environment
has obvious effects on the health of the human body and
has achieved certain research results, there are still some
problems: (1) Lack of basic theoretical research and
multidisciplinary communication. At present, most stud-
ies are based on qualitative or quantitative analysis of
evidence-based medicine, lacking basic theoretical re-
search of forestry. Medical scholars lack guidance from
forestry scholars, relying on subjective or instantaneous
forest environmental factor data to determine whether a
particular forest has health benefits and environmental
factors that lead to increased risk of bias. Forest scholars
lack guidance from medical scholars, and the trial partic-
ipants are mostly healthy young people, most of whom
fail to consider ethical issues and measure physiological
indicators. Some scholars [45,46] conduct small sample
studies with homemade scales that fail to pass the reli-
ability and validity test, and the evidence is not convin-
cing enough. (2) The risk of bias in the papers is
relatively high. Overall, in the 28 papers included in the
study, the random sequence generation, the allocation
concealment, and the application of blinded methods are
important sources of bias. Loss to follow-up, reported
adverse events, and intervention-measures or control-
measure compliance are the secondary sources of bias.
The forest environment is also one of the potential
sources of bias.
Interdisciplinary communication between forestry and
medicine is an important measure to reduce the bias
caused by environmental factors. The forest environ-
ment mainly affects human health through “five senses
experience,”relying on the synergistic effect between a
series of forest environmental factors (such as phyton-
cide, negative air ions, oxygen, and forest microclimate).
These environmental factors have significant seasonal,
diurnal, and regional variations. The tree species
composition and color and forest density are also im-
portant influencing factors and can affect human health,
especially mental health. Forest environmental factors in
individual studies show that phytoncide with antioxi-
dant and antiseptic enhance immunity function [51,
56]. Air negative ions have the effect of increasing
parasympathetic activity, relieving depression, and
lowering blood glucose [57–59]. The forest microcli-
mate can improve human thermal comfort and reduce
heat stress [60,61]. A large area of green in the for-
est can bring a sense of security and calm and signifi-
cantly reduce anxiety and negative emotions [62].
Comprehensive analysis of the forest environment and
dynamic monitoring of key environmental factors are
important to judge the potential health benefits of the
forest and reveal the healthcare mechanism of forest
bathing. This has important guiding significance for
the formation of industry standards and the establish-
ment of a forest bathing base.
Reducing the risk of bias is an urgent problem to
be solved in medical empirical research of forest
bathing, for example, RCT, a method of random se-
quence generation which should be described in de-
tail. The study of low bias risk should use random
number tables, computer software for random num-
ber generation, flipping a coin, rolling dice, shuffling
cards, or envelopes, etc., rather than odd and even
numbers, date of birth, subjective assignment, etc. In
forest bathing trials, it is complicated to assign con-
cealment and apply a blind method to participants
and personnel. If trial conditions are limited, a cross-
over study can be added to reduce the risk of bias,
but the length of the washout period should be con-
sidered to avoid a carryover effect. Blind methods
should be applied to data collectors and outcome as-
sessors to reduce the risk of bias, as conditions per-
mit. Generally, participants are subjectively more
inclined to participate in the forest bathing group
than the control group. If the guide introduces too
much information about the healthcare efficacy of
forest bathing, this may give the participants psycho-
logical hints, which may increase the risk of bias. Due
to the small number of forest bathing test samples
and relatively short trial time, the proportion of par-
ticipants lost to follow-up is small. In case of follow-
up loss, the risk of bias can be reduced by estimating
the missing data and conducting intention-to-treat
analysis. Adverse events such as snake bites, pollen al-
lergies, falls, and bruises were rarely mentioned in the
forest bathing study. Adverse events during the trial
should be explained in the paper. Compliance with
intervention or control measures is also rarely men-
tioned in forest bathing studies, especially for forest
bathing activities greater than one day. Participant
compliance with intervention measures such as walk-
ing, making crafts, meditating, and taking classes, as
well as compliance with restrictions or prohibitions
on the use of electronic products, communication,
caffeine intake, smoking, and drinking, should be
explained.
Wen et al. Environmental Health and Preventive Medicine (2019) 24:70 Page 18 of 21
Conclusion
Forest bathing activities may significantly improve people’s
physical and psychological health. In terms of medical em-
pirical studies on forest bathing, the methodological quality
of RCTs is significantly higher than that of NRCTs. In the
future, medical empirical studies of forest bathing should
reinforce basic studies and interdisciplinary exchange to en-
hance the methodological quality of papers while decreas-
ing the risk of bias, thereby raising the grade of paper
evidence.
Appendix
Table 4 Search words (subject word and random word)
Intervention Outcome Combined
terms
1) Forest bathing/ 17) Health care/ 37) 16
AND 36
2) Forest nature
convalescent/
18) Healing/
3) Forest therapy/ 19) Therapy/
4) Shinrin-yoku/ 20) Recover/
5) Forest travel/ 21) Vigor/
6) Forest walking/ 22) Spirit/
7) Forest yoga/ 23) Pressure/
8) Forest/ 24) Depression/
9) Forest meditation/ 25) Anxiety/
10) Forest environment/ 26) Brain wave/
11) Forest areas/ 27) Pulse/
12) Phytoncide/ 28) Heart rate/
13) Negative air ions/ 29) Blood pressure/
14) Negative oxygen ions/ 30) Blood glucose/
15) Oxygen/ 31) Saliva/
16) 1 OR 2 OR 3 OR 4 OR 5
OR 6 OR 7 OR 8 OR 9 OR 10
OR 11 OR 12 OR 13 OR 14
OR 15
32) Inflammatory factor/
33) Immune/
34) Hormonal readiness/
35) Skin conductance/
36) 17 OR 18 OR 19 OR 20
OR 21 OR 22 OR 23 OR 24
OR 25 OR 26 OR 27 OR 28
OR 29 OR 30 OR 31 OR 32
OR 33 OR 34 OR 35
Abbreviations
HRV: Heart rate variability; IL: Interleukin; lnHF: The natural logarithmic value
of the high frequency of heart rate variability; lnLF: The natural logarithmic
value of the low frequency of heart rate variability; NK: Nature killer;
NRCT: Non-randomized controlled trial; RCT: Randomized controlled trial;
SBP: Systolic blood pressure
Acknowledgements
Not applicable
Authors’contributions
YL and XG conceived this study. YW analyzed the data and was a major
contributor in writing the manuscript. YW, QY, and YP conducted the
systematic review. All authors read and approved the final manuscript.
Funding
This work was supported by funds from the National Natural Science
Foundation of China (31660230).
Availability of data and materials
Not applicable
Ethics approval and consent to participate
Not applicable
Consent for publication
Not applicable
Competing interests
The authors declare that they have no competing interests.
Author details
1
College of Forestry, Jiangxi Agricultural University, 1101 ZhiMin Road,
Nanchang 330045, China.
2
Jiangxi Academy of Forestry, 1629 FengLin Road,
Nanchang 330032, China.
Received: 22 July 2019 Accepted: 1 October 2019
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