Original Article
A Review of Field Experiments on the
Effect of Forest Bathing on Anxiety
and Heart Rate Variability
Marc R Farrow, PT1 and Kyle Washburn, RN, BSN, CEN2
Global Advances in Health and Medicine
Volume 8: 1–7
! The Author(s) 2019
Article reuse guidelines:
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DOI: 10.1177/2164956119848654
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Abstract
Many studies have explored the physiological and psychological benefits of the Japanese nature therapy practice of “shinrin-
yoku,” known in the West as forest bathing. This review article has narrowed its focus to include the most recent literature
about the beneficial effects of forest bathing on heart rate variability, expressed as an increase in InHF, indicating activation of
the parasympathetic nervous system and also its effect on reducing anxiety.
Keywords
forest bathing, shinrin-yoku, anxiety, heart rate variability
Received January 3, 2019; Revised received April 3, 2019. Accepted for publication April 8, 2019
Introduction
Urbanization continues to increase worldwide, and
by 2050, 68% of the population is projected to live in
an urban environment.1 This trend has a negative
impact on physical and emotional health. “Overall,
urbanicity seems to be linked to a higher risk of
mental health disorders.”2
Anxiety disorders are the most prevalent psychiatric
disorders. According to epidemiological surveys, one-
third of the population is affected by an anxiety disorder
during their lifetime. They are more common in women.
During midlife, their prevalence is highest. These disor-
ders are associated with a considerable degree of impair-
ment, high health-care utilization and an enormous
economic burden for society.3
This review aims to consider if the practice of forest
bathing may be a valuable intervention to treat anxiety
and boost parasympathetic responses.
scientific rationale for forest walks. Most of the guided
walks I’ve been on in Japan begin and end with measure-
ments of blood pressure and salivary amylase, which are
indicators of stress and relaxation.” For the purposes of
this article, the forest bathing model entails an average
of 2 to 4 hours in a forest and includes a combination of
various activities such as walking, standing, lying, sit-
ting, and deep breathing. This practice is facilitated by
a trained forest bathing guide to focus participants’
attention with meditative concentration on sensory expe-
riences, engaging sight, sound, touch, smell, and some-
times taste to explore the surrounding forest.6 Forest
bathing can be defined as immersion in nature with
mindful use of all 5 senses; studies on physical and
mental health benefits report reduced stress, anxiety,
and depression symptoms as well as improved mood
and relaxation.7
Background
Forest bathing is a nature therapy originally developed
in Japan as shinrin-yoku, a term coined in 1982 by
Tomohide Akiyama of the Japanese Forestry Agency.4
This therapeutic technique can be described as “bathing
in the forest atmosphere, or taking in the forest through
our senses.”5 Clifford notes “the Japanese emphasize the
1Winston-Salem Forest Bathing, Lexington, North Carolina
2Wake Forest University School of Medicine, Winston-Salem,
North Carolina
Corresponding Author:
Marc R Farrow, Winston-Salem Forest Bathing, Lexington, NC, USA.
Email: wsforestbathing@gmail.com
Creative Commons Non Commercial CC BY-NC: This article is distributed under the terms of the Creative Commons Attribution-
NonCommercial 4.0 License (http://www.creativecommons.org/licenses/by-nc/4.0/) which permits non-commercial use, reproduction and dis-
tribution of the work without further permission provided the original work is attributed as specified on the SAGE and Open Access pages (https://us.
sagepub.com/en-us/nam/open-access-at-sage).
2
Global Advances in Health and Medicine
Methods
A broad review of the available literature was conducted
using the PubMed and ScienceDirect databases with the
keywords: “shinrin-yoku,” “forest therapy,” “forest
walking,” and “nature therapy”; 631,953 references
were found with this search. The results were narrowed
to recent field experiments with dates ranging from 2008
to 2018 that also used a formalized forest bathing
program affecting anxiety levels and heart rate variabil-
ity; however, other studies using similar methods of
exposure to natural settings were also included due to
the limited amount of recent research specifically related
to a formalized forest bathing program. Inclusion crite-
ria for these additional field experiments are defined as
walking in a forest for a determined amount of time.
Some studies were excluded in which surveys were
given or lab experiments were conducted where
participants were presented with images or other natural
stimuli versus actually walking in natural surroundings.
Nine articles were selected for this review.
Effects on Parasympathetic Nervous
System Activity
Research observing the effects of forest bathing/forest
therapy on the autonomic nervous system (measuring
an increased heart rate variability as an indicator) were
found with 2 studies.
The first study analyzed the heart rate variability
(HRV) of 485 young male participants while walking
in forest versus urban environments. HRV data were
obtained while groups walked “in a forest or an urban
environment for approximately 15 minutes. On the
second day, the participants switched field sites.”8
During forest walking, larger parasympathetic indica-
tor of HRV (InHF) and smaller sympathetic indicator of
HRV (In(LF/HF)) were observed compared with those
walking in urban environments. As the InHF and In
(LF/HF) are indicators of parasympathetic and sympa-
thetic activity, the results implied that the autonomic
relaxation occurred during walking in forest environ-
ments. Parasympathetic activation (using HRV as an
autonomic nervous system indicator) while walking in
forest environments has been established in previous
field experiments by the same authors and are confirmed
by this study. It is important to note that increased InHF
indicates an increase in parasympathetic activation
response: lowered heart rate and blood pressure, and a
calm mood state. Conversely, increased In(HF/LF) indi-
cates a heightened state, or “fight or flight” response.
In addition, previous studies suggest that InHF differs
between viewing and walking, with an increase in InHF
evident with walking.8
In the second study, “autonomic responses to urban
and forest environments were studied in 625 young male
subjects.”9 The participants were randomly divided into
2 groups that viewed either a forest or urban landscape
for 15 minutes each in a seated position. HRV was mon-
itored continuously. “The experiment was performed at
each experimental site over 2 consecutive days.”9 On day
2, the subjects switched environments, repeating the
protocol from the first day.
“Approximately 80% of the subjects showed an
increase in the parasympathetic activity”9 in a forest set-
ting and the urban subjects exhibited the opposite effect.
The measured variations in InHF between forest and
urban locations measured reveal that 79.2% of the 625
subjects experienced an increase in InHF when exposed
to a forest setting; conversely, 20.8% of the 625 subjects
experienced a decrease in InHF. In addition, difference
in the InHF mean values is statistically significant,
although minute. Similar results were found for ln
(LF/HF) values, indicating HRV may be a more sensi-
tive tool for measuring parasympathetic activation in
this experiment.9
In this third study evaluating the cardiovascular
effects of nature on women, 36 female subjects, aged
30 to 50 years, were selected. In randomly changing
groups of fours, the subjects were exposed to an urban
area, an urban park, or an urban forest. Seated exposure
time was 15 minutes and walking exposure time was
30 minutes. Measurements gathered include blood pres-
sure, heart rate, and electrocardiogram to determine
HRV. Breathable particulate matter and noise levels
were also recorded in each setting. Substantially reduced
levels of particulate air pollution and noise levels were
recorded in natural areas, while higher levels of noise
and breathable particulate matter were found with city
exposures. The data analysis revealed that exposure to
natural settings shows increased high frequency (HF)
power and a lower heart rate, indicating an increase in
parasympathetic nervous activity. Viewing natural set-
tings compared to viewing city areas yields similar
results as well as reduced systolic blood pressure.
In general, the results of this study indicate that even
brief exposure to a natural setting may result in reduced
cardiovascular risk. Furthermore, high noise levels and
increased levels of air pollution outdoors appear to have
a negative effect on cardiovascular benefit. The authors
noted that the combined measures of HRV and heart
rate are a more sensitive measure of stress response in
short-term field experiments in comparison to similar
studies using cortisol levels as a stress indicator.
Limitations noted in this field experiment include a
small sample size and the absence of male subjects in
this study.10
Farrow and Washburn
3
Effects on HRV and Anxiety Levels
Several other articles consider the effects of forest bath-
ing/forest therapy on anxiety-tension using The Profile
of Mood States (POMS) subscale scores and the seman-
tic differential (SD) method.
One such study measured changes in autonomic ner-
vous system activity and emotions after a 2-hour forest
bathing program in 128 middle-aged and elderly partic-
ipants. Physiological measurements were taken; pulse
rate, blood pressure, HRV, and POMS subscale scores
were recorded.
The POMS “subscale scores for ‘tension-anxiety’,
‘anger-hostility’, ‘fatigue-inertia’, ‘depression-dejection’,
and ‘confusion-bewilderment’ were significantly lower,
whereas the positive mood subscale score of ‘vigor-activ-
ity’ was higher.”11 In addition, participants reported sig-
nificantly lower levels of anxiety using the Spielberger
State-Trait Anxiety Inventory. This study determined
that a forest bathing program causes significantly
lower pulse rate, systolic, and diastolic blood pressure
after a 2-hour walk. In addition, reduced tension, anger,
fatigue, depression, confusion, anxiety and improved
positive emotions were reported. Surprisingly, sympa-
thetic and parasympathetic nerve activity measures
revealed no significant changes. In summary, a 2-hour
forest bathing program appears to yield physiological
and psychological benefits with middle-aged and elderly
individuals.
In another study, 20 Japanese men were screened and
10 were selected for 2 groups of 5. Each participant had
been diagnosed with stage 1 hypertension (having a sys-
tolic 140–159 mm Hg or diastolic 90–99 mm Hg) and 5
had stage 2 hypertension (having a systolic 160–179 mm
Hg or diastolic 100–109 mm Hg). Each group alternated
walking in a forest setting for 17 minutes one day fol-
lowed by walking for 17 minutes in an urban setting the
next day. Heart rate and HRV were used to quantify
autonomic nervous system responses. Subjects complet-
ed 2 questionnaires measuring mood states using the
modified SD method referencing 3 pairs of adjectives
on 13 scales: “comfortable to uncomfortable,” “relaxed
to awakening,” and “natural to artificial.” A modified
30-question POMS was set for 6 subscales: “tension-
anxiety,” “depression,” “anger-hostility,” “fatigue,”
“confusion,” and “vigor.”
Results indicated that walking in a forest elicited both
physiological and psychological relaxation for middle-
aged individuals with hypertension; there was a signifi-
cant increase in parasympathetic nerve activity and a
significant decrease in heart rate. In addition, a signifi-
cant increase in “comfortable,” “relaxed,” and “natural”
mood, and reduced “tension-anxiety,” “depression,”
“anger-hostility,” “fatigue,” “confusion,” and “vigor”
were reported. The authors point out this study’s
limitations, including an inability to generalize these
results for the female population and for people of vary-
ing ages, and thus a more comprehensive study is rec-
ommended in the future.12
A third article investigated the influence of forest
therapy on cardiovascular effects. “Forty-eight young
adult males participated in the two-day field research”13
comparing physiological and psychological changes
during forest walking and urban walking. Changes in
HRV, heart rate, and blood pressure were measured
and questionnaires recorded changes in mood states
following walking. Subjective measures such as
“comfortable-uncomfortable,” “natural-artificial,” and
“soothed-aroused” were recorded using a 13-scale SD
method. The modified 30-question version of the
POMS questionnaire was used to measure mood.
Anxiety was measured using the Spielberger State-Trait
Anxiety Inventory questionnaire. Each group walked for
14 minutes in each environment.
The study found forest walking significantly increased
In(HF) values and significantly decreased In(LF/HF)
values compared to urban walking. Heart rate during
forest walking was significantly lower than the urban
walking control group. Reported subjective measures
indicated that “negative mood states and anxiety levels
decreased significantly by forest walking compared with
urban walking.”12 “Walking in a forest environment
may promote cardiovascular relaxation by facilitating
the parasympathetic nervous system. In addition,
forest therapy may be effective in reducing negative psy-
chological symptoms.”13
Another study examined the effects of walking in a
forest on HRV and mood states, comparing natural set-
tings to city environments. Over the course of 2 years, 24
field experiments were done with 280 Japanese male par-
ticipants to compare the findings regarding the physio-
logical effects of forest walking with corresponding
results from previous research. Each experiment was
comprised of 12 subjects divided into 2 groups of 6.
One group was assigned to walk in a city while the alter-
nate group walked in a forest environment. Each group
walked approximately 14 minutes. On the following day,
the groups alternated settings. Blood pressure, heart
rate, HRV, and salivary cortisol levels were recorded
prior to and following each walk. All cardiac data
were collected with a portable electrocardiograph, and
both HF and low frequency (LF) power level compo-
nents were calculated each minute during walking.
Psychological status was measured using the POMS
recording 6 dimensions of mood: tension-anxiety,
depression-dejection, anger-hostility, fatigue, confusion,
and vigor.
Results indicated reduced salivary cortisol levels after
walking or viewing natural environments, with a 2.4%
decrease when walking is compared to viewing.
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Global Advances in Health and Medicine
Significantly lower average pulse rates were recorded in a
natural setting versus a city environment, and walking
resulted in lower rates than viewing. Comparable results
were also seen in the reduced average diastolic blood
pressure after walking in versus simply viewing nature.
In addition, a 102% increase in InHF after walking and
a 56% increase after viewing with a corresponding
reduction in In(LF/HF) were measured. POMS score
results indicate that natural settings (versus urban envi-
ronments) reduce tension/anxiety, depression, anger,
confusion, as well as increase vigor, and that walking
in nature yields significantly greater effects as compared
with viewing natural settings.
In summary, exposure to forest bathing, when com-
pared to exposure to urban settings, may reduce heart
rate, cortisol levels, blood pressure, and increase parasym-
pathetic nervous system activity indicating a lower stress
response. These findings, along with past studies, establish
a strong case that exposure to nature has a positive
impact on human physiology and mental health.14
Effects on Anxiety
Additional studies considered the influence of forest
bathing/forest therapy on anxiety levels in participants.
One study recorded the effects of forest bathing on
cardiovascular function and mood states in 19 middle-
aged hypertensive subjects while walking in a forest
versus during urban walking. Forest park walking for
80 minutes “significantly reduced the pulse rate in
middle-aged males with higher blood pressure, com-
pared with walking in an urban area.”15 Pulse rate is
an index of autonomic nervous system activity indicating
a state of relaxation.
Results included decreased pulse rate, a decrease in
urinary dopamine, tendency toward decreased urinary
adrenaline, a decrease in adiponectin in serum, in addi-
tion to a significantly increased score for vigor, and
decreased scores for depression, anxiety, fatigue, and
confusion (using POMS). In contrast, urban walking sig-
nificantly increased scores for fatigue and reduced scores
for vigor. As found in previously discussed studies, the
cumulative effect suggests a forest bathing program
induces a significant physiological and psychological
state of relaxation.15
Two studies authored by Ochai et al. explored the
physiological effects of a forest therapy program on
middle-aged females and males, respectively. In the
first study, 17 middle-aged Japanese females were select-
ed to determine the effects of a formalized forest therapy
regimen on both physiological and psychological status.
Subjects took a 4-hour 41-minute walk; systolic, diastol-
ic BP, and pulse rates were recorded, and salivary sam-
ples were taken to obtain a reliable measure of cortisol
levels, as an increase in cortisol indicates stress.
Data were gathered the day before the walk and follow-
ing forest therapy. Urinary adrenaline, noradrenaline,
and salivary cortisol levels were measured to determine
sympathetic activity. The SD method and short form of
the POMS were used to measure psychological status.
The SD method used 3 pairs of adjectives on 7-point
scales: “comfortable to uncomfortable,” “relaxed to
awakening,” and “natural to artificial”. The short form
of POMS included 3 subscales: “tension–anxiety,”
“fatigue,” and “vigor.”
Pulse rate was shown to be notably lower following
forest therapy versus the prior day, while salivary corti-
sol levels were also significantly lower. Significantly
higher SD scores were reported for “comfortable,”
“relaxed,” and “natural” following forest therapy than
on the prior day. In addition, the POMS scores revealed
a significant improvement in mood; the negative sub-
scale “tension–anxiety” was significantly lower and the
positive range of the emotional subscale “vigor” was sig-
nificantly higher following forest therapy. The mean
pulse rate was significantly lower as well after forest
therapy when compared to the prior day, indicating a
state of relaxation. Lab results also revealed that salivary
cortisol levels were significantly lower following forest
therapy than the day before. The authors conclude
that forest therapy also reduces stress in middle-aged
females but recognize that this study had the limitation
of excluding an urban walk control group in order to
compare results with the forest therapy group.16
In the second study, 9 Japanese males ranging in age
from 40 to 72 years were selected as participants in a
study to assess the physiological and psychological
effects of forest therapy on middle-aged males with
high-normal blood pressure (systolic 130–139 mm Hg
and/or diastolic 85–89 mm Hg). Each participant
engaged in a 4-hour 35-minute forest therapy walk.
Blood pressure and several physiological and psycholog-
ical indicators of stress were measured at the same time
of day on the day prior to and following forest therapy.
Urine and blood samples were also taken, measuring
adrenaline, cortisol, and creatinine. Questionnaires
were completed by subjects the day before and following
forest therapy. The SD method, POMS subscale scores,
and combined POMS Total Mood Disturbance (TMD)
score were used to evaluate psychological responses
to forest therapy. The SD method used 7-point scales
for 3 pairs of adjectives, such as “comfortable to
uncomfortable,” “relaxed to awakening,” and “natural
to artificial”. The short-form POMS scores used 30 ques-
tions with the following 6 subscales: “tension-anxiety,”
“confusion,” “anger-hostility,” “depression,” “fatigue,”
and “vigor.” The TMD score was calculated by using the
POMS 6 subscales values, and a high TMD score corre-
lates with a negative psychological state.
Farrow and Washburn
5
This study demonstrated that forest therapy facili-
tates a significant decrease in blood pressure and a
decrease in serum cortisol levels and urinary adrenaline.
Also reported were an increase in “natural” and
“relaxed” feelings measured by the modified SD
method, “a decrease in POMS negative subscales ‘ten-
sion-anxiety’, ‘confusion’, and ‘anger-hostility’, as well
as the TMD score in middle-aged males with high-
normal blood pressure.”17 The authors recognize the
limitations of this study due to lack of a control group
walking in an urban setting.17 The results of the above
discussed studies are summarized in Table 1.
Analysis
It is evident that more research is required to further
explore the beneficial health effects of a formalized
forest bathing program as only 3 of the 10 articles
reviewed here chose an accepted forest bathing model
in their experimental design (Yu and Ochiai). One
study (Lanki) closely approximated a forest bathing
program, during which subjects were guided through
numerous activities engaging the 5 senses. The remaining
6 research articles relied only on walking in and/or view-
ing a forest environment. A consistent use of a formal-
ized forest bathing program would ensure more reliable
outcomes in further research in this area.
Of the reviewed studies, 40% of the researchers select-
ed young participants in their 20s, while the majority
chose subjects aged 30 to 69 years. This is a limitation;
it will be advantageous for future researchers to include
a broader range of ages, equally represented, in order to
generalize results across the population.
It is notable that only 1 study included both male and
female subjects in their experimental design. This may be
of importance as there is evidence there may be physio-
logical differences in how men and women respond to
stress.18 Studies reviewed included 70% male partici-
pants, 20% female participants, and 10% mixed group.
It is advisable to consider a more heterogeneous sample
in the experimental design with regard to gender. It is
also of interest to note that 60% of the reviewed studies
had sample sizes less than 100 participants.
Table 1. A Summary of Research Studies.
Study Author
Kobayashi et al.8
Kobayashi et al.9
Lanki et al.10
Yu et al.11
Song et al.12
Lee et al.13
Park et al.14
Li et al.15
Location
Japan
Japan
Finland
Taiwan
Japan
Japan
Japan
Japan
Number
of Subjects
485
625
36
43/85
20
48
280
19
Gender of
Subjects
M
M
F
M/F
M
M
M
M
Age of Subjects
(Mean Æ Standard
Deviation)
21.7 Æ 1.6
21.6 Æ 1.6
30-60
(age range)
60.0 Æ 7.44
58.0 Æ 10.6
21.1 Æ 1.2
21.7 Æ 1.5
51.2 Æ 8.8
Exposure
Time in
Minutes
15
15
30
120
17
14
16 Æ 5
14 Æ 2
80
Stimuli vs
Control
F vs U
F vs U
F vs U
Before FB
vs after FB
F vs U
F vs U
F vs U
F vs U
Follows
FB Model
No
No
Closely
approximates
Yes
No
No
No
No
Results
" INHF
" INHF
" INHF
# Anxiety
# HR
# BP
# Anxiety
" INHF
# Anxiety
" INHF
# Anxiety
" INHF
# Anxiety
# HR
# SC
# Anxiety
# HR
Ochiai et al.16 Japan
17
F
62.2 Æ 9.4
281
FB vs control Yes
Ochiai et al.17 Japan
9
M
56.0 Æ 13.0
275
FB vs control Yes
# Anxiety
# HR
# SC
# Anxiety
# BP
# SC
# UA
Abbreviations: BP, blood pressure; F, forest; FB, forest bathing; HR, heart rate; INHF, average power of the high-frequency component of heart rate
variability; SC, salivary cortisol; U, urban; UA, urinary adrenaline.
6
Global Advances in Health and Medicine
Another result of this review highlights that the inci-
dence of increased InHF occurred in all 6 articles eval-
uating the effect of HRV while exposed to a natural
environment. These provide strong evidence that forest
bathing may elicit parasympathetic nervous activity.
Based on the studies reviewed here, it is evident that
forest bathing and exposure to nature approximating
this model, even for as little as 15 minutes, may be of
benefit in reducing anxiety and stress. However, there
were wide variances in exposure time across these stud-
ies, from 15 minutes to over 4 hours. Fifteen minutes
was the most frequent exposure time used (55% of stud-
ies reviewed). It would be of interest if future research
could determine if longer times result in stronger results,
or perhaps additional health benefits. It is also notable
that significant physiological benefits were also found by
simply viewing a forest setting; however, the effect has
been less than with walking.14
Limitations
This review raises questions regarding what would be con-
sidered a minimal as well as an optimal therapeutic dose
for time spent forest bathing in order to maximize physi-
ological and mood benefits. Further field experiments
would be justified to determine if longer exposure times
would yield even more health benefits yet to be deter-
mined. It should be considered whether benefits are depen-
dent on specific amounts of exposure time, as there
appears to be no standard used for research purposes cur-
rently. In addition, a standardized forest bathing program
would improve the reliability of future research studies.
For results to apply to broader populations, it would
also be of benefit to select a more heterogeneous mix of
participants, as several studies referenced here chose either
male or female subjects within a determined age range.
Moreover, larger sample sizes would also contribute to
more reliable results, improved precision, and a better
understanding of the potential benefits of forest bathing.
Conclusions
The field experiments referenced here provide limited but
strong and consistent evidence that exposure to forest
bathing/forest therapy results in an increase in InHF
associated with activation of the parasympathetic ner-
vous system and also reduced anxiety. Additional ther-
apeutic benefits include positive mood states and
improved mental coordination, with a reduction in
stress levels and lower blood pressure.
Future Studies
The results from the inclusion criteria in this review
yielded a very low sample of articles on the effects of
forest bathing/forest therapy on anxiety levels and HRV.
Ongoing exploration of the practice of forest bathing is
needed in order to better understand the mechanisms
activating the parasympathetic nervous system and
how this may be used as a safe, economic, and effective
method of treating anxiety as an adjunct therapy to med-
ication and cognitive-based therapy. Additional field
experiments are recommended to establish a standard
for exposure time, a standardized forest bathing pro-
gram, and appropriate subject selection criteria to be
used in future studies.
Declaration of Conflicting Interests
The author(s) declared no potential conflicts of interest with
respect to the research, authorship, and/or publication of
this article.
Funding
The author(s) received no financial support for the research,
authorship, and/or publication of this article.
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