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Effects of forest environment (Shinrin-yoku/Forest
bathing) on health promotion and disease prevention
—the Establishment of “Forest Medicine”—
Qing Li＊
＊
Correspondence: qing-li@nms.ac.jp
Department of Rehabilitation Medicine, Graduate School of Medicine, Nippon Medical School, Tokyo, Japan.
Abstract
Humans have enjoyed forest environments for ages because of the quiet atmosphere, beautiful scenery, mild climate, pleasant aromas,
and fresh, clean air. In Japan, since 2004, serial studies have been conducted to investigate the effects of forest environments (Forest
bathing/Shinrin-yoku) on human health. My research team has established a new medical science called Forest Medicine. The Forest
Medicine is a new interdisciplinary science, belonging to the categories of alternative medicine, environmental medicine and
preventive medicine, which studies the effects of forest environments (Forest bathing/Shinrin-yoku) on human health. It has been
reported that Forest bathing/Shinrin-yoku has the following beneficial effects on human health:
1 Shinrin-yoku increases human natural killer (NK) activity, the number of NK cells, and the intracellular levels of anti-cancer
proteins, suggesting a preventive effect on cancers.
2 Shinrin-yoku reduces blood pressure and heart rate showing preventive effect on hypertension and heart diseases.
3 Shinrin-yoku reduces stress hormones, such as urinary adrenaline and noradrenaline and salivary/serum cortisol contributing to
stress management.
4 Shinrin-yoku increases the activity of parasympathetic nerves and reduces the activity of sympathetic nerves to stabilize the
balance of autonomic nervous system.
5 Shinrin-yoku improve sleep.
6 Shinrin-yoku increases the levels of serum adiponectin and dehydroepiandrosterone sulfate.
7 In the Profile of Mood States (POMS) test, Shinrin-yoku reduces the scores for anxiety, depression, anger, fatigue, and
confusion, and increases the score for vigor, showing preventive effects on depression.
8 Shinrin-yoku may apply to rehabilitation medicine
9 Shinrin-yoku in city parks also has benefits on human health.
10 Shinrin-yoku may have preventive effect on COVID-19 by boosting immune function and by reducing mental stress.
Taken together, these findings suggest that Shinrin-yoku may have potential preventive effects on non-communicable diseases.
Keywords: Blood pressure, Forest bathing, Forest Medicine, Immune function, NK, Nervous system, Phytoncide, POMS, Shinrin-
yoku, Stress hormone
What is Shinrin-yoku/Forest bathing?
Humans have enjoyed forest environments for ages be-
cause of the quiet atmosphere, beautiful scenery, mild cli-
mate, pleasant aromas, and fresh, clean air. Researchers in
Japan have tried to find preventive effects against non-
communicable diseases from forests and have proposed a
new concept called “Shinrin-yoku/Forest bathing”[1–3].
Shinrin-yoku is translated into Forest bathing in Eng-
lish. Shinrin in Japanese means ‘forest’, and yoku means
‘bath’. Therefore, Shinrin-yoku means bathing in the forest
atmosphere, or taking in the forest through our senses.
This is not exercise, or hiking, or jogging. It is simply
being in nature, connecting with it through our sense of
sight, hearing, taste, smell and touch. Shinrin-yoku is like
a bridge. By opening our senses, it bridges the gap be-
tween us and the natural world [1,2].
People can enjoy the Shinrin-yoku through all five
senses [3].
1. Sense of sight: green color, yellow color and red
color, forest landscape, etc.
2. Sense of smell: special good smell, fragrance from
trees and flowers, phytoncides.
3. Sense of hearing: forest sounds, listen to the birds
singing and the breeze rustling in the leaves of the
trees.
Environmental Health and
Preventive Medicine
Environmental Health and Preventive Medicine (2022) 27:43
https://doi.org/10.1265/ehpm.22-00160
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4. Sense of touch: touching trees, put your whole body
in the forest atmosphere.
5. Sense of taste: eating foods and fruits from forests,
taste the fresh air in forests.
Why forest bathing/shinrin-yoku is necessary?
Stress is a keyword to understand why Shinrin-yoku is
necessary in Japan. In 1984, the word ‘technostress’was
coined to describe unhealthy behaviour around new tech-
nology. Technostress can arise from all manner of every-
day usage, like checking your phone constantly, compul-
sively sharing updates and feeling that you need to be
continually connected. Symptoms run from anxiety, head-
aches, depression, mental fatigue, eye and neck strain to
insomnia, frustration, irritability and loss of temper [4].
Since the year 2000, we have officially become an urban
species. The urban population worldwide grew from just
746 million in 1950 to 3.9 billion in 2014, according to the
United Nations Population Division. By 2050, 75% of the
world’s projected 9 billion population will live in cities
[2]. In Japan, prevalence of cancers and non-communica-
ble diseases such as heart disease, diabetes, cerebrovascu-
lar disease and hypertension are increasing [5]) and more
than half of deaths are attributed to non-communicable
diseases [6]. According to the Ministry of Health, Labour
and Welfare of Japan, the percentage of workers with
anxiety and stress was more than 50% in 1982, 62.8% in
1997, 58% in 2007, and 60.9 in 2012 [3], suggesting a
major mental health problem. Stress can induce almost all
non-communicable diseases, such as cancers, hyperten-
sion, depression, cardiovascular diseases, stroke, gastric
ulcer, obesity, alcoholism, panic disorder, eating disorder
[7]. Therefore, the health management of workers, espe-
cially in relation to stress-related diseases, has become a
major social issue and an effective new method for pre-
vention of diseases is needed. There is also the phenome-
non known as karoshi, or death from overwork in Japan.
In 2016, the Ministry of Health, Labour and Welfare of
Japan released a Cabinet-endorsed white paper on the ex-
tent of working overtime in Japan. Almost 23 per cent of
companies said their employees worked more than eighty
hours of overtime a month. Of those companies, 11.9%
said some employees worked more than a hundred hours
of extra time a month [2]. It is urgent to establish preven-
tive measures against stress and non-communicable dis-
eases; however, effective prevention methods have not
been established. The forest environment has long been
enjoyed for its quiet atmosphere, beautiful scenery, calm
climate, clean fresh air and special good smell. Empiri-
cally, forest environments may reduce stress and have a
relaxing effect; therefore, walking in forest parks may have
beneficial effects on human health. Based on the above
background, in Japan, a national health programme for
Forest-bathing or Shinrin-yoku began to be introduced in
1982 by the Forest Agency of Japan for the stress manage-
ment of workers in Japan. In 2005, my research team
conducted the first Shinrin-yoku study in Iiyama, Nagano
prefecture in Japan and the terms of Shinrin-yoku and
Forest Bathing in English were first named and defined
by author in this study [1]. Shinrin-yoku is also a short
leisurely visit to a forest field, which is similar in effect to
natural aromatherapy, for the purpose of relaxation and the
breathing in of volatile substances called phytoncides
(wood essential oils) derived from plants (trees), such as
alpha-pinene and limonene [1,8–10]. Because forests oc-
cupy 67% of the land in Japan, Shinrin-yoku is easily
accessible [11]. It has become a recognized relaxation
and/or stress management activity in Japan. Shinrin-yoku
as a method of preventing diseases and promoting health is
becoming a focus of public attention. According to a pub-
lic opinion poll conducted in Japan in 2003, 25.6% of
respondents had participated in a Shinrin-yoku trip, indi-
cating its popularity in Japan [3]. Currently, the terms of
“Shinrin-yoku”and “Forest bathing”are internationally
accepted because both “Shinrin-yoku”and “Forest bath-
ing”are the titles of English books [2,12] and books in
other languages [13,14].
What is Forest Medicine?
Imagine a new medical science that could let you know
how to be more active, more relaxed, healthier and happier
with reduced stress and reduced risk of non-communicable
diseases. and cancers by visiting forests. This new medical
science is Forest Medicine. Forest Medicine studies the
effects of forest environments on human health and is a
new interdisciplinary science, belonging to the categories
of alternative medicine, environmental medicine and pre-
ventive medicine [3]. Forest Medicine is developed from
Forest bathing or Shinrin-yoku and forest therapy and is an
evidence-based preventive medicine. Forest Therapy is al-
so developed from forest bathing (shinrin-yoku), which is
a research-based healing practice through immersion in
forest environments with the aim of promoting mental
and physical health and improving disease prevention
while at the same time being able to enjoy and appreciate
the forest. Forest therapy is defined as a proven Shinrin-
yoku effect (https://www.fo-society.jp/).
Why forest medicine is necessary?
In Japan, a national health programme for Shinrin-yoku
was proposed by the Forest Agency of Japan in 1982 for
reducing stress in workers and the promotion of human
health. However, when people started to practise Shinrin-
yoku, in the early 1980s, it was based only on common
sense and the intuitive idea that being in the beautiful
green forests of Japan would be good for us. There has
not been sufficient medical evidence supporting the bene-
ficial effects of Shinrin-yoku due to technical limitations
regarding measurements, and evidence-based evaluations
as well as a therapeutic menu of Shinrin-yoku have been
requested. Against this background, the Japanese Society
Environmental Health and Preventive Medicine (2022) 27:43 2of10
ofForestTherapywasestablishedin2004(https://
www.fo-society.jp/) for conducting the evidence-based re-
search on the effects of forest environments on human
health. The Ministry of Agriculture, Forestry and Fisheries
of Japan initiated a research project between 2004 and
2006 and organized a project team to investigate the ther-
apeutic effects of forests on human health from a scientific
perspective. In addition, recent technological develop-
ments have enabled us to determine the effects of forest
environments on human health. Some people study forest,
some people study medicine, I study forest medicine to
find the beneficial effects of Shinrin-yoku on human
health.
Evidence-based Forest Medicine
In Japan, since 2004, serial studies have been conducted to
investigate the effects of forest bathing/shinrin-yoku (for-
est environments) on human health by the project team.
My research team has obtained a vast amount of data,
proving that forest bathing promotes both physical and
mental health by reducing stress [3].
1. Effects of Shinrin-yoku on immune system
It is well known that immune system including natural
killer (NK) cells plays an important role in defense against
bacteria, viruses and tumors. It is also well known
that stress inhibits immune function. Forest environment
(Shinrin-yoku/forest bathing) may reduce stress. There-
fore, the author speculated that forest environment may
have beneficial effect on immune function by reducing
stress [3]. Thus, my research team conducted several ex-
periments to investigated the effects of Shinrin-yoku on
human immune function.
1-1 Effect of Shinrin-yoku on human NK activity in male
subjects
In the first Shinrin-yoku study [1], 12 healthy male sub-
jects, aged 37–55 years, were selected from three large
companies in Tokyo, Japan. The information of the sub-
jects gathered from a self-administered questionnaire, in-
cluding age and lifestyle habits. None of the subjects had
any signs or symptoms of infectious diseases, used drugs
that might affect immunological analysis, or were taking
any medication at the time of the study. The subjects par-
ticipated in a three-day/two-night trip to forest areas at
Iiyama in Nagano prefecture located in the Chubu (central)
region of Japan in early September, 2005. On day 1, the
subjects walked about 2.5 km. This level of exertion was
selected because it closely resembles the average amount
of physical activity in a normal working day. This walk
was conducted in the forest park during the afternoon.
Participants were allowed to rest anywhere and anytime
they chose. On day 2, they walked about 2.5 km over two
hours both in the morning and afternoon, respectively, in
two different forest parks; and on day 3, the subjects fin-
ished the trip and returned to Tokyo after blood was drawn
and a questionnaire survey was completed. The forests
included Japanese cedar (Cryptomeria), Japanese beech,
and Japanese oak. Blood was sampled on the second and
third days. White blood cell (WBC) counts, NK activity,
numbers of NK and T cells, and numbers of granulysin
(GRN), perforin, and granzymes A and B (GrA/B)-ex-
pressing lymphocytes were measured in the blood sam-
ples. The same measurements were made before the trips
on a normal working day as a control. Blood was sampled
at 8:00 am on all occasions. To control for the effect of
alcohol on NK activity, the subjects did not consume al-
cohol for 2 days before blood was drawn. Phytoncide
concentrations in forest air samples were also measured.
Walk in forests significantly increased human NK activity
and the numbers of NK cells. NK cell activity went up
from 17.3% to 26.5% with a 53.2% increase. NK cell
numbers went up from 440 to 661 with a 50% increase.
It has been reported that NK cells kill tumor or virus-in-
fected cells by the release of perforin, granzymes, and
GRN via the granule exocytosis pathway [15]. In order
to explore the mechanism of enhancement of NK activity
induced by the forest bathing, the effect of forest bathing
on the intracellular levels of perforin, GRN, and GrA/B in
peripheral blood lymphocytes (PBL) were investigated,
and it was found that the forest bathing also significantly
increased the numbers of intracellular perforin-, GRN-,
and GrA/B-expressing lymphocytes. The presence of
anti-cancer protein GRN was up by 48%, GrA by 39%,
GrB by 33%, and perforin by 28%. Taken together, these
findings indicate that Shinrin-yoku can increase NK activ-
ity, and that this effect might be at least partially mediated
by increasing the number of NK cells and by the induction
of intracellular perforin, GRN, and GrA/B [1]. Han et al.,
[16] and Tsao et al., [17] also reported that forest bathing
increased human NK activity and supported our findings.
1-2 Does a trip to places without forest (a city tourist visit) also
increase human NK activity?
Although a forest bathing trip boosted human NK activity,
does a trip to places without forest (a city tourist visit) also
increase NK activity? Thus, to investigate whether taking a
trip (city tourist visit) can also affect human NK activity,
eleven healthy male subjects, aged 35–56 years, partici-
pated in a three-day/two-night trip to Nagoya city, which is
the fourth most populous city in Japan in mid-May, 2006
[8]. Information on the subjects was gathered from a self-
administered questionnaire, including age and lifestyle
habits as described previously [1]. On the first day, the
subjects walked for two hours in the afternoon along a
tourist route through a historic district in Nagoya, and then
stayed at a hotel also in Nagoya. On the second day, the
subjects walked for 2 hours around the Nagoya Baseball
Dome in the morning and 2 hours around/in Nagoya Air-
port in nearby Nagoya city in the afternoon. There are
some areas with trees in Nagoya city, but there are almost
no trees in the areas visited. The class of hotel was the
same and the lifestyle of the subjects during the stays in
Environmental Health and Preventive Medicine (2022) 27:43 3of10
the hotels was the same for the city and the forest trips.
The walking courses in the trip were 2.5 km, which was
the same as the previous study [1]. Blood was sampled at
8:00 am on the second and third days after the trip, and
three days prior to the trip as a control. WBC counts, NK
activity, proportions of NK and T cells, and GRN-, perfor-
in-, and GrA/B-expressing cells in PBL were measured.
Adrenaline concentration in urine was also measured. The
results showed that the city tourist visit did not increase
human NK activity, numbers of NK cells, or the expres-
sion of the selected intracellular perforin, GRN, and GrA/
B, indicating that increased NK activity during forest bath-
ing trip was not due to the trip itself, but due to forest
environments [8].
1-3 How long does the increased NK activity last after a forest
bathing trip?
Forest bathing, but not a city trip indeed boosted human
NK activity; however, how long does the increased NK
activity last after a forest bathing trip? Thus, an investiga-
tion was conducted to address this question [8]. Twelve
healthy male subjects, aged 35–56 years, were selected
from four large companies in Tokyo, Japan. Information
on the subjects was gathered from a self-administered
questionnaire, including age and lifestyle habits as describ-
ed previously [1]. The subjects experienced a three-day/
two-night trip to three different Chamaecyparis obtuse
(Japanese cypress, Hinoki in Japanese) forest parks, the
birthplace of forest bathing (shinrin-yoku) in Japan, around
Agematsu town in Nagano prefecture located in the Chubu
(central) region of Japan in early September, 2006. The
schedule of the forest bathing trip was similar to that de-
scribed previously [1]. Blood was sampled at 8:00 am on
the second and third days, on days 7 and 30 after the forest
bathing trip, and three days prior to the trip as a control.
WBC counts, NK activity, proportions of NK and T cells,
and GRN-, perforin-, and GrA/B-expressing cells in PBL
were measured. Spot urine was sampled at 7:00 am on the
second and third days, on days 7 and 30 after the forest
bathing trip, and three days prior to the trip as a control.
Adrenaline concentration in urine was also measured. The
forest bathing trip significantly increased human NK ac-
tivity, the numbers of NK cells, and the percentages of
GRN-, perforin-, and GrA/B-expressing cells in PBL,
which confirmed the previous findings [1]. The increased
NK activity, number of NK cells, and percentages of
GRN-, perforin-, and GrA/B-expressing cells lasted more
than 7 days and even for 30 days in the cases of NK
activity, the number of NK cells, and GRN- and GrB-ex-
pressing cells. These findings indicate that a forest bathing
trip increased NK activity, the number of NK cells, and the
levels of intracellular perforin, GRN, and GrA/B, and that
these effects lasted for at least seven days after the trip,
even 30 days [8]. The important finding is that visiting a
forest, rather than a city, increases NK activity and the
intracellular levels of perforin, GRN, and GrA/B. It is very
important in the preventive medicine.
1-4 Effect of Shinrin-yoku on human NK activity in female
subjects
Although it has been demonstrated that forest bathing trips
enhance human NK activity in male subjects, it still re-
mained to be resolved whether or not a Shinrin-yoku trip
also increases NK activity in female subjects. It has been
reported that menstrual cycle significantly affects NK ac-
tivity [18]; therefore, the influence of menstrual cycle on
NK activity should be controlled for in experiments with
female subjects.
In this study [9], thirteen healthy nurses, aged 25–43
years, professional career 4–18 years, were selected with
informed consent. None of the subjects had any signs or
symptoms of infectious disease, used drugs that might
affect immunological analysis, or were taking any medi-
cation at the time of the study. The subjects experienced a
three-day/two-night trip to forest fields around Shinano
town in Nagano prefecture located in the Chubu (central)
region of Japan in early September of 2007. The schedule
of the forest bathing trip and blood/urine sampling was
similar to that described previously. WBC counts, NK
activity, numbers of NK and T cells, and GRN, perforin,
and GrA/B-expressing lymphocytes in the blood samples,
the concentrations of estradiol and progesterone in serum,
the concentrations of adrenaline and noradrenaline in urine
were measured. The same control measurements were
made before the trip on a normal working day. Blood
was sampled at 8:00 am on all days. The concentrations
of phytoncides in the forests were also measured. The
forest bathing trip significantly increased NK activity
and the positive rates of NK, perforin-, GRN-, and GrA/
B-expressing cells. The increased NK activity and the pos-
itive rates of NK, perforin, GRN, and GrA/B-expressing
cells lasted for more than seven days after the trip [9],
which confirmed the previous findings in male subjects
[8]. Phytoncides, such as ¡-pinene and ¢-pinene were de-
tected in forest air. These findings indicate that a forest
bathing trip also increased NK activity, the number of NK
cells, and the levels of intracellular anti-cancer proteins in
female subjects, and that this effect lasted for at least seven
days after the trip.
It has been reported that the menstrual cycle and the
levels of estradiol and progesterone in serum may affect
human NK activity in female subjects [18–20]. To control
for the influence of menstrual cycle on NK activity, a
questionnaire was administered to obtain information on
the menstrual cycle of the subjects. The ratios of subjects
who were in the follicular phase during the experiment
were 5/13, 6/13, 6/13, 7/13, and 6/13 on the day before
the trip, days 1 and 2 during the trip, and days 7 and 30
after the trip, respectively, indicating that there was no
significant difference in the proportion of the menstrual
cycles of the subjects between the different days. This
suggests that the menstrual cycle had a similar influence
on the average of NK activity on the different days. In
addition, there was no significant difference in the concen-
trations of estradiol and progesterone in the serum in the
Environmental Health and Preventive Medicine (2022) 27:43 4of10
days before, during, and after the forest bathing trip,
indicating that estradiol and progesterone had a similar
effect on NK activity on different days in the subjects in
this case [9].
1-5 A day trip to a forest park also increased human NK activity
Although a three-day/two-night Shinrin-yoku enhanced
human NK activity, the number of NK cells, and intra-
cellular anti-cancer proteins in lymphocytes, it is not clear
whether a day trip to a forest park also increases human
NK activity. My research team found that a day trip to a
forest park also significantly increased human NK activity,
the numbers of NK, perforin, GRN, and GrA/B-expressing
cells while significantly decreasing the concentrations of
cortisol in the blood and adrenaline in urine in male sub-
jects. The increased NK activity lasted for seven days after
the trip. Phytoncides, such as isoprene, ¡-pinene and ¢-
pinene, were detected in the forest air [21]. In fact, NK
activity was increased after day 1 in three-day/two-night
forest bathing [1,8,9]; therefore, the day trip of forest
bathing [21] reproduced the previous findings [1,8,9].
The increased NK activity and anti-cancer proteins
lasted for more than 7 days, even 30 days after the trip
[1,8,9,21,22]. This suggests that if people take a forest
bathing trip once a month, they may be able to maintain a
higher level of NK activity. This is very important in terms
of health promotion and preventive medicine. NK cells are
immune cells and play an important role in defense against
bacteria, viruses and tumors. People with higher NK ac-
tivity showed a lower incidence of cancers, whereas peo-
ple with lower NK activity showed a higher incidence of
cancers [23], indicating the importance of NK cell function
on cancer prevention. Therefore, it suggests that Shinrin-
yoku may have the preventive effect on cancers.
Many factors, including circadian variation [24], phys-
ical exercise [25], and alcohol consumption [25,26] can
affect human NK activity. In order to control for the effect
of circadian rhythm on NK activity, blood was sampled at
8:00 am on all days [1,8,9,21,27]. To control for the
effect of physical exercise on NK activity, the walking
steps during the trips were limited to the average normal
workday distances as monitored by a pedometer. The lev-
els of physical activity among all trips were also matched.
To control for the effect of alcohol on NK activity, the
subjects did not consume alcohol for two days before
blood was drawn during the study period for both trips
including before the trips and after the trips on days 7
and 30.
These findings indicate that forest therapy increased NK
activity by the following pathways [22].
(1) Shinrin-yoku directly acts on NK cells by phyton-
cides released from trees and induces increases in
the number of NK cells and the levels of intracel-
lular anti-cancer proteins such as perforin, GRN,
and GrA/B.
(2) Shinrin-yoku indirectly increases human NK activ-
ity, the number of NK cells and the levels of intra-
cellular anti-cancer proteins by reducing stress hor-
mones.
Taken together, because NK cells can kill tumor cells by
releasing anti-cancer proteins, such as perforin, GRN, and
GrA/B, and forest therapy increases NK activity and the
intracellular level of anti-cancer proteins, the above find-
ings suggest that Shinrin-yoku may have a preventive ef-
fect on cancer generation and development. My research
team also reported that people living in areas with lower
forest coverage have significantly higher standardized
mortality ratios (SMRs) of cancer than people living in
areas with higher forest coverage. There are significant
inverse correlations between the percentage of forest cov-
erage and the SMRs of lung, breast, and uterine cancers in
females, and the SMRs of prostate, kidney, and colon
cancers in males in all prefectures in Japan, even after
the effects of smoking and socioeconomic status are fac-
tored in, indicating that increased forest coverage may
partially contribute to a decrease in mortality due to cancer
in Japan [11]. This an ecological study and the evidence
level of ecological study is limited.
2. Effects of Shinrin-yoku on the nervous system
Forests also regulates the nervous system. The nervous
system is made up of the sympathetic nervous system
(the ‘fight or flight’part, which gets your heart going),
and the parasympathetic nervous system (the ‘rest and
recover’part, which calms everything down). Common
sense tells us that spending time in nature helps us relax
and feel calm [28]. Many studies have reported that Shin-
rin-yoku can increase the activity of parasympathetic nerve
and reduce the activity of sympathetic nerve showing re-
laxing effects (psychologically calming effects) [29–36].
3. Effects of Shinrin-yoku on stress hormones
There are three kinds of stress hormones: adrenaline
(which mainly indicates mental stress), noradrenaline
(which mainly indicates physical stress) and cortisol
(which can indicate both) [28]. Adrenaline is released from
the adrenal medulla, and the adrenaline level increases
under circumstances of novelty, anticipation, unpredict-
ability, and general emotional arousal, whereas noradrena-
line is the predominant neurotransmitter released by the
sympathetic system, and some of this enters the blood;
the level of noradrenaline increases during increased phys-
ical activity [37]. Cortisol is released by the hypothalamic-
pituitary-adrenal axis in response to stress [31]. My re-
search team has found that Shinrin-yoku and phytoncides
can reduce stress hormones, such as adrenaline, noradrena-
line and cortisol and may contribute to stress management
[8,9,21,27,29,36]. In addition, because the effect of
forest bathing on adrenaline was greater than that on nor-
adrenaline, the effect on mental stress was greater than on
physical stress [3,9]. Other researchers also reported that
Shinrin-yoku reduced cortisol in saliva [31,32] which
supported our findings.
Environmental Health and Preventive Medicine (2022) 27:43 5of10
4. Effects of Shinrin-yoku on blood pressures and
heart rate
Many reports have found that forest environments reduced
the levels of blood pressure in middle-aged subjects with
high-normal blood pressure [29,38–42].
Li et al. [29] investigated the effects of forest environ-
ments on blood pressure in sixteen male subjects with
higher blood pressure without taking antihypertensive
drug (mean age: 57.4 «11.6 years) after obtaining in-
formed consent. The subjects took day trips to a forest
park in the suburbs of Tokyo and to an urban area of
Tokyo as a control in September 2010. On both trips, they
walked for two hours in the morning and afternoon on a
Sunday. Blood and urine were sampled on the morning
before each trip and after each trip. Blood pressure was
measured on the morning (8:00 am) before each trip, at
noon (1:00 pm), in the afternoon (4:00 pm) during each
trip, and on the morning (8:00 am) after each trip. Both
systolic and diastolic blood pressure levels at noon
(1:00 pm) in the forest park were significantly lower than
those in the urban area. Moreover, the diastolic blood
pressure level in the afternoon (4:00 pm) in the forest park
was significantly lower than that in the urban area. How-
ever, there was no significant difference in both systolic
and diastolic blood pressure levels before walking
(8:00 am) between the urban and forest. The reductions
in blood pressure after walking in a forest environment
were 7 mmHg for both SBP (from 141 to 134 mmHg),
and DBP (from 86 to 79 mmHg). This suggests that walk-
ing in the forest park, but not in the urban area reduced
blood pressure and that forest therapy has a potential pre-
ventive effect on hypertension.
Mao et al [39] also found the beneficial effect of forest
bathing on blood pressure. In this study, twenty-four eld-
erly patients with essential hypertension were randomly
divided into two groups of 12. One group was sent to a
broad-leaved evergreen forest to experience a 7-day/7-
night trip, and the other was sent to a city area in Hang-
zhou for control. Blood pressure indicators, cardiovascular
disease-related pathological factors including endothelin-
1, homocysteine, renin, angiotensinogen, angiotensin II,
angiotensin II type 1 receptor, angiotensin II type 2 recep-
tor as well as inflammatory cytokines interleukin-6 and
tumor necrosis factor ¡were detected. As results, subjects
who walked in the forest environment showed a significant
reduction in blood pressure in comparison to that of the
city group. The values for the bio-indicators in subjects
exposed to the forest environment were also lower than
those in the urban control group and the baseline levels of
themselves. They concluded that forest bathing has ther-
apeutic effects on human hypertension by inhibiting the
renin-angiotensin system and inflammation. In addition,
Ochiai et al. [38] and Yu et al. [40] also found that forest
bathing can reduce blood pressure on middle-aged males
with high-normal blood pressure. Moreover, Ideno et al
[41] conducted a systematic review and meta-analysis in-
cluding twenty trials involving 732 participants on the
effect of Shinrin-yoku on the blood pressure. Both systolic
and diastolic blood pressures of the forest environment
was significantly lower than that of the non-forest environ-
ment showing a significant effect of Shinrin-yoku on re-
duction in blood pressure. Yau and Loke [42] also re-
viewed the physiologically and psychologically relaxing
effects of forest bathing on middle-aged and elderly people
with pre-hypertension and hypertension, indicating that
forest bathing shows preventive effect on hypertension.
Li et al [36] also found that forest bathing reduced heart
rate in middle-aged males.
Taken together, Shinrin-yoku reduces blood pressure by
the following mechanisms:
1) Shinrin-yoku reduces blood pressure by reducing
stress hormone levels, such as urinary adrenaline,
urinary noradrenaline [8,9,21,29,36], salivary cor-
tisol [31,32], and blood cortisol [21] levels. It is well
known that stress hormones such as adrenaline, nor-
adrenaline and cortisol increase blood pressure level.
2) Shinrin-yoku reduces blood pressure by reducing
sympathetic nerve activity and by increasing para-
sympathetic nerve activity. Sympathetic nerve activ-
ity can be determined by measuring the levels of
urinary adrenaline and/or noradrenaline [8,9,43],
and there are significant correlations between blood
pressure and urinary adrenaline and noradrenaline
levels [44]. In addition, many studies [31–33,36]
reported that forest viewing and walking in forests
significantly reduced sympathetic nerve activity and
increased parasympathetic nerve activity compared
to performing the same activities in an urban envi-
ronment.
3) Shinrin-yoku reduces blood pressure by inhibiting
the renin-angiotensin system [39].
5. Potential preventive effects of Shinrin-yoku on
depressed states
Shinrin-yoku can reduce the symptoms for anxiety, de-
pression, anger, fatigue and confusion and increased the
vigor in the Profile of Mood States (POMS) test in both
male and female subjects [1,3,7,9,21,29–36,45]. In
addition, forest bathing is particularly effective against
mental stress (mental fatigue) [3]. Li et al [46] reported
that Shinrin-yoku significantly increased level of serotonin
in serum, and significantly increased the score for vigor
and decreased the score for fatigue in the POMS test. Furu-
yashiki et al [47] conducted a comparative study of the
physiological and psychological effects of a day-long ses-
sion of Shinrin-yoku on working age people with and with-
out depressive tendencies and demonstrated significant
positive effects on mental health, especially in those with
depressive tendencies. These studies suggest Shinrin-yoku
has a preventive effect on subjects in a depressed state.
6. Effect of Shinrin-yoku on sleep
Three studies investigated the effect of Shinrin-yoku on
sleep [3,46,48,49]. We previously found that Shinrin-
Environmental Health and Preventive Medicine (2022) 27:43 6of10
yoku significantly increased sleep time in middle-aged
male office workers [3]. Recently, my research team found
that Shinrin-yoku significantly improved the sleepiness on
rising and the feeling refreshed (recovery from fatigue)
assessed by the Oguri-Shirakawa-Azumi sleep inventory
MA version (OSA-MA), indicating that Shinrin-yoku may
improve sleep quality [46,48]. Morita et al [49] also re-
ported that two hours of forest walking improved noctur-
nal sleep conditions for individuals with sleep complaints,
possibly as a result of exercise and emotional improve-
ment.
7. Effect of Shinrin-yoku on adiponectin
Adiponectin is a serum protein hormone specifically pro-
duced by adipose tissue. Studies have shown that lower
blood adiponectin concentrations are associated with sev-
eral metabolic disorders, including obesity, type 2 DM
(diabetes mellitus), cardiovascular disease, and metabolic
syndrome. Recent studies have suggested that adiponectin
shows anti-tumorigenesis activity in several cancers, in-
cluding prostate, breast, endometrial, brain, and colon can-
cer [50,51]. My research team found that Shinrin-yoku
can increase the level of serum adiponectin [29,36]. How-
ever, there are only two studies on the effect of forest
bathing on adiponectin so far; therefore, further studies
on this topic are needed.
8. Effect of Shinrin-yoku on dehydroepiandrosterone
sulfate (DHEA-S)
Levels of DHEA and DHEA-S, the major secretory prod-
ucts of the adrenal gland, decline dramatically with age,
concurrent with the onset of degenerative changes and
chronic diseases associated with aging [52,53]. Epidemio-
logical evidence in humans suggests that DHEA-S has
cardioprotective, antiobesity, and antidiabetic properties
[53]. My research team found that Shinrin-yoku signifi-
cantly increase serum dehydroepiandrosterone sulfate
(DHEA-S) levels [29]. On the other hand, Kim et al [54]
reported that a Forest Healing Program in a Korean forest
reduced DHEA-S levels. Therefore, the effect of forest
bathing on DHEA-S needs further research.
9. Shinrin-yoku may apply to rehabilitation medicine
Depression is reportedly the most common mental disorder
following stroke, with an incidence ranging from 10 to
64%. Poststroke depression has an adverse effect on func-
tional recovery and increases the mortality rate [55,56]. In
addition, nearly one-third of patients suffer from depres-
sion and more than one-quarter of patients suffer from
PTSD after an acute orthopaedic injury [57]. Based on
the above background, the prevention of depression in
rehabilitation hospital is a big challenge in the world. It
is urgent to establish preventive measures against depres-
sion; however, effective prevention methods have not been
established at present. My research team previously found
that the Shinrin-yoku significantly increased the score for
vigor and decreased the scores for anxiety, depression,
anger, fatigue, and confusion in the POMS test accompa-
nied by reductions in urinary adrenaline and noradrenaline
concentrations in both males and females, suggesting that
forest bathing may have potential preventive effects on
depression. Moreover, we also found that walking in city
parks in Tokyo reduces the negative emotions such as
tension–anxiety, anger, depression, fatigue and confusion
and increase in feelings of vigor in the POMS test and
showed the relaxing effect both in male and female sub-
jects [1,3,9,21,29–36,45,48]. These findings suggest
that Shinrin-yoku may have a potential preventive effect
on depressive status. Thus, my research team investigated
the relaxing effects of Shinrin-yoku on rehabilitation pa-
tients by walking in a Japanese garden for applying the
forest bathing in stress management and prevention of
depression in patients in rehabilitation hospitals to improve
the rehabilitative effect. My research team found that Shin-
rin-yoku in a Japanese garden reduces the scores of anxi-
ety, depression, anger, fatigue and confusion, whereas in-
crease the score of vigor in patients in a rehabilitation
hospital suggesting that Shinrin-yoku may show apply to
the stress management and depression prevention [48,58].
Some patients who have experienced stroke and acute or-
thopedic injuries and cannot walk also can enjoy Shinrin-
yoku in a wheelchair.
10. Effect of phytoncides released from trees on
human health
Why did the forest environment affect human health?
What kind of factors in the forest environment contribute
to beneficial effects on human health? The quiet atmos-
phere, beautiful scenery, mild climate, special good smell,
and fresh, clean air in forests contribute to the effects. It is
the total effect from all five senses: senses of sight, smell,
hearing, touch and taste. In fact, sense of smell by breath-
ing in volatile organic substances, called phytoncides from
trees, such as ¡-pinene and limonene has a bigger effect
[27,59]. My research team found that phytoncides re-
leased from trees significantly increased human NK activ-
ity and the intracellular levels of perforin, GrA, and GRN
in human NK cells both in vitro [59] and in vivo [27].
Phytoncide exposure significantly decreased the concen-
trations of adrenaline and noradrenaline in urine, indicate
that phytoncide exposure and decreased stress hormone
levels may partially contribute to increased NK activity
[27].
11. The potential preventive effect of Shinrin-yoku
on non-communicable diseases
It has been reported that stress may induce and/or exacer-
bate many non-communicable diseases, such as cancers,
hypertension, ischemic heart disease, gastrointestinal ul-
cer, and depression [7]. Shinrin-yoku can reduce stress
hormone levels, such as urinary adrenaline, urinary nora-
drenaline [8,9,21,29,36], salivary cortisol [31,32], and
blood cortisol [21] levels suggesting that Shinrin-yoku
may have preventive effects on non-communicable dis-
Environmental Health and Preventive Medicine (2022) 27:43 7of10
eases mediated by reducing the stress hormones. It has
been reported that Shinrin-yoku reduces blood pressure
and heart rate showing potential preventive effect on hy-
pertension [29,36,38,39]. It also has been reported that
Shinrin-yoku effectively decreases blood glucose levels in
type 2 DM (diabetes mellitus) patients and shows preven-
tive effect on type 2 DM [60]. In addition, Shinrin-yoku
shows potential preventive effects on depression by reduc-
ing stress hormones [8,9,21,29,31,32,36], by reducing
negative emotions such as anxiety, depression, anger, fa-
tigue, confusion, and by increasing the level of serotonin
in serum and the positive feelings such as vigor [1,3,7,
21,29–36,45,46]. Shinrin-yoku-induced increases of the
level of serum adiponectin [29,36] and DHEA-S [29] also
contribute to this effect. Moreover, Shinrin-yoku may have
preventive effects on cancers by increasing anticancer pro-
teins in NK cells, such as perforin, granulysin and gran-
zymes [1,8,9,21,27].
12. Potential preventive effects of Shinrin-yoku on
COVID-19
Elderly people, patients with underlying diseases such as
diabetes, hypertension, heart diseases and respiratory dis-
eases are easy to develop COVID-19 and become more
severe, and the mortality rate is also higher because of the
reduced immune function in these patients [61]. Therefore,
immune function is very important to prevent COVID-19.
Shinrin-yoku may have preventive effect on COVID-19 by
boosting immune function [22]. Mental stress and various
mental disorders due to “lockdown”and “isolation”are
also major social problems [62]. Shinrin-yoku reduces
the negative emotions, mental stress and stress hormones,
and increases vigor [1,3,8,9,29,36]. In fact, my research
team has found that virtual exposure to forest environ-
ments based on audio-visual stimuli brought by a short
computer video showing forest environments, with an ur-
ban video as a control showed effective to reduce negative
emotions such as anxiety in people forced by lockdown
in limited spaces in Italy during COVID-19 pandemic
[62]. Kim et al also reported the positive effects of a Forest
Healing Program in a Korean forest on motional stress and
sleep quality for exhausted medical workers during the
COVID-19 Outbreak in Korea [54]. Therefore, Shinrin-
yoku may have preventive effect on COVID-19-induced
mental stress and mental disorders. Shinrin-yoku also has
preventive effects on hypertension and heart diseases [29,
36] to prevent COVID-19.
Taken together, Shinrin-yoku will play a very important
role on the preventive of COVID-19 by boosting immune
function and by reducing mental stress in post-COVID-19
health management and disease prevention.
Wen et al [63] conducted a systematic review in studies
on forest bathing (Shinrin-yoku) and concluded that forest
bathing (Shinrin-yoku) might have the following merits:
remarkably improving cardiovascular function, hemody-
namic indexes, neuroendocrine indexes, metabolic in-
dexes, 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.
Forest Medicine in the future
Based on the above background, I would like to propose
the following international collaborations on Forest Med-
icine in the future.
1. To expand the philosophy and concept of Forest Med-
icine over the world.
2. To verify the preventive effects of Forest Medicine on
non-communicable diseases in the world.
3. To establish an international accreditation system for
Forest Medicine specialist and Forest Therapist.
4. To establish the Shinrin-yoku/Forest bathing as a treat-
ment for some non-communicable diseases.
5. To incorporate the Forest Medicine into Rehabilitation
Medicine.
Declaration
Ethics approval and consent to participate
All studies were conducted under the Declaration of Helsinki. The Ethics
Committees of the Nippon Medical School and Nagano Prefectural Kiso Hospital
approved all studies. Written informed consent was obtained from all subjects
after a full explanation of the study procedures.
Consent for publication
Not applicable.
Availability of data and material
The datasets used and analyzed during the current study are available on
reasonable request to the corresponding author.
Competing interests
The authors declare that they have no competing interests.
Fundings
These studies were conducted and supported by the following fundings.
1. A research project for utilizing advanced technologies in agriculture, forestry
and fisheries of Japan (2004–2006).
2. Grants-in-Aid for Scientific Research from the Ministry of Education, Culture,
Sports, Science and Technology (No. 16107007).
3. Research projects from the National Land Afforestation Promotion Organ-
ization
4. A research project from the Forestry and Forest Products Research Institute
(2009–2010)
5. A research project from Japan Society for the Promotion of Science (JSPS)
(2011–2012).
6. A research project from the Ministry of Agriculture, Forestry and Fisheries
Strategic Innovation Creation Program
7. Research projects from the Vehicle Racing Commemorative Foundation of
Japan (2013–15, 2019).
Conflict of interest
The author is a board member of the Japanese Forest Therapy Society Board of
Directors.
Author’s contribution
Qing Li wrote this review.
Environmental Health and Preventive Medicine (2022) 27:43 8of10
Authors’information
Qing Li, MD, PhD, clinical professor, Department of Rehabilitation Medicine,
Graduate School of Medicine, Nippon Medical School, Tokyo, Japan, Vice-
President & Secretary General of International Society of Nature and Forest
Medicine (INFOM), President of Japanese Society of Forest Medicine, Director of
Forest Therapy Society (NPO corporation).
Acknowledgements
My research was supported by the Ministry of Agriculture, Forestry and Fisheries
Advanced Project Research Project, a grant from the Ministry of Education,
Culture, Sports, Science and Technology, the Ministry of Agriculture, Forestry and
Fisheries Strategic Innovation Creation Program, the National Land Afforestation
Promotion Organization, Japan Society for the Promotion of Science (JSPS),
Forestry and Forest Products Research Institute, and the Vehicle Racing
Commemorative Foundation of Japan. I would like to thank the collaborators
from Nippon Medical School, Forestry and Forest Products Research Institute,
International Society of Nature and Forest Medicine (INFOM), Nagano Prefectural
Kiso Hospital, Forest Therapy Society, Forest Therapy Bases, Sakurakouseien
Hospital, and Misato Care Center for their cooperation in this research.
Received: 9 July 2022, Accepted: 20 September 2022
Published online: 1 November 2022
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