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The Impact of Virtual Nature Therapy on Stress Responses: A Systematic Qualitative Review

Review

The Impact of Virtual Nature Therapy on Stress Responses: A

Systematic Qualitative Review

Sharifah Shuthairah Syed Abdullah 1, Dayang Rohaya Awang Rambli 1, Suziah Sulaiman 1 , Emad Alyan 1,* ,

Frederic Merienne 2 and Nadia Diyana 3

1 Department of Computer and Information Sciences, Universiti Teknologi PETRONAS,

Seri Iskandar 32610, Perak, Malaysia; s_shuthairah89@yahoo.com (S.S.S.A.);

dayangrohaya.ar@utp.edu.my (D.R.A.R.); suziah@utp.edu.my (S.S.)

2 Arts et Metiers Institute of Technology, LISPEN, HESAM Université, UBFC,

F-71100 Chalon-sur-Saône, France; frederic.merienne@ensam.eu

3 School of Multimedia Technology and Communication, Universiti Utara Malaysia,

Sintok 06010, Kedah Darul Aman, Malaysia; nadia.diyana@uum.edu.my

* Correspondence: emad.alyan@utp.edu.my

Citation: Syed Abdullah, S.S.;

Awang Rambli, D.R.; Sulaiman, S.;

Alyan, E.; Merienne, F.; Diyana, N.

The Impact of Virtual Nature Therapy

on Stress Responses: A Systematic

Qualitative Review. Forests 2021, 12,

1776. https://doi.org/10.3390/

f12121776

Academic Editor: Luis Diaz-Balteiro

Abstract: This study aims to review the key ﬁndings of past studies that assessed the impact of

virtual environments, such as nature and forests for stress therapy. Previous research has found that

virtual reality (VR) experiences affect socio-affective behavior, indicating the potential of using VR

for cognitive and psychological stress therapy. However, evidence for the impacts of virtual forest

therapy as a stress-reduction technique is lacking, and the usefulness of these techniques has yet to be

determined. This review was carried out following the preferred reporting items for meta-analyses

and systematic reviews. It summarized the literature and provided evidence on virtual forest therapy

(VFT) effectiveness in stress relief. We conducted a literature search considering VR-related studies

published from 2013 until June 2021 for different databases, including Embase, Medline/PubMed,

Hindawi, ScienceDirect, Scopus, Web of Science, Taylor & Francis, and the Cochrane Library, to

see how effective VFT reduces stress levels and improves mental well-being. According to the set

inclusion criteria, eighteen relevant papers detailing original research were eligible for inclusion.

This overview suggests that VR provides beneﬁts for assessing and reducing stress levels. While

real natural environments effectively promote recovery from stress, virtual exposure to nature

also positively affects stress. Thus, VR could be an effective technique for promoting relaxation,

particularly during the COVID-19 pandemic, where stress levels rise globally. However, more

in-depth studies are required to substantiate this potential ﬁeld of VR relaxation.

Received: 12 November 2021

Accepted: 10 December 2021

Published: 15 December 2021

Keywords: virtual reality (VR); virtual forest therapy (VFT); virtual nature; stress; psychology

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1. Introduction

Nature has played an essential role in people’s lives [1,2]. Today, however, our ties

to mother nature are tenuous at best. People can boost sensory awareness and balance

their lives by taking soothing and meditative walks in nature. Nature walks are based on a

Japanese technique known as “shinrin-yoku”, which translates to “forest bathing” and is

sometimes referred to as “forest therapy” [3]. This technique was ﬁrst developed in the

early 1980s by Tomohide Akiyama, director of the Japanese Forestry Agency [4], based on

the idea that cultivating a love relationship with nature can help preventative healthcare,

well-being, and healing. In addition to Japan, several other developed countries in Europe

and North America have practiced these natures’ walk methods to reduce stress levels in

patients [5].

Consequently, the impacts of forests and nature on human well-being and health have

piqued researchers’ interest in recent years. Forest therapy is a therapeutic, immersive

environmental experience that promotes well-being [6]. It also has been shown to have

Forests 2021, 12, 1776. https://doi.org/10.3390/f12121776

https://www.mdpi.com/journal/forests

Forests 2021, 12, 1776

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a beneﬁcial inﬂuence on the health of the human body and mind. According to previous

studies, intensive involvement with nature, such as “shinrin-yoku”, can be helpful to health.

This claim has been supported by numerous studies in the medical ﬁeld [7–10]. A study

by [6] found that, compared to an urban environment, two days of forest bathing could

increase the number of natural killer cells in the immune system, signiﬁcantly increase

parasympathetic nervous activity, and suppress substantially sympathetic activity in the

participants. Another study revealed that looking out a hospital window at trees helped

patients recover faster after surgery, implying that a visual component alone can improve

human health [11]. It showed that visual aspects, such as merely viewing the green forest

environment, may be a source of positive beneﬁts and apparently reﬂect on people’s

psychological state throughout their time in the forest. Today, people are occupied with

everyday life, and most reside in cities where noise pollution, air pollution, water pollution,

work pressure, and lack of green environments are available. These conditions lead to

stress symptoms in a large portion of the urban population [12]. Stress levels will increase

in the following 30 years due to an increase in development [13–16]. Other than that, lack

of time because of work makes it difﬁcult for people to spend time going to places that

can relieve stress. However, instead of stepping outside, new technology based on virtual

reality (VR) has been introduced to allow us to bring forest, park, or nature into the house.

VR can be deﬁned as a class of computer-controlled multisensory communication

technology that enables more natural interaction with data and engages the human senses

in new ways [17]. Another deﬁnition of VR is a computer-created environment in which

the user feels existent [18]. The modern technological advances in VR have become

a useful supporting tool in several environments, such as disorder therapies [19–21],

rehabilitation processes [22–24], marketing [25–27], industry [28,29], or safety and industrial

training [30,31]. VR systems are also increasing promptly, with countless new applications

in the ranges of healthcare and psychology [32]. Researchers may ﬁne-tune the design and

elaboration of environmental settings using VR, bypassing the limits of ﬁeld studies, which

cannot account for a wide range of potentially confounding elements (e.g., temperature,

crowd, trafﬁc).

Furthermore, VR can develop a strong sense of presence, deﬁned as the personal

sensation of being there in a virtual environment [33]. It simulates experimental scenarios

where comparable real-life situations are unavailable (e.g., forest with or without river). VR

can be executed by using a ﬂat-screen display [34], a projection-based cube room known

as a computer-automated virtual environment [35], or a head-mounted display [36]. The

use of ﬂat-screen displays and the other two visualization technologies offer an immersive

experience in which the user is entirely encircled by the virtual environment, generating a

more real-life experience.

Nowadays, people spend more time indoors than outdoors, especially during the

period of the COVID-19 pandemic. This tendency has caused individuals to be isolated

from contact with nature, negatively inﬂuencing their mental and physical health. The

human mind has become stressed and depressed owing to various problems such as self-

harm and eventually suicide. Therefore, human beings need to ﬁnd something to be free

from stress and lead to a healthy lifestyle.

Many studies have been using stress as a health-related variable, revealing that pro-

longed stress can affect health and have a negative effect on a person [37,38]. It has been

shown that stress is linked to various cardiovascular diseases and mental disorders [12,39,40].

In 1991, the theory of stress relief was proposed by [41] to improve psychology, which states

that acquaintance with the natural environment can decrease stress and directly affect men-

tal recovery. In other words, exposure to nature views or simulations of nature may help

individuals recover from psychological and physiological-related stress. Psychotherapists

consider VR therapy (VRT) one of the most promising psychiatric interventions in the

future decades to treat mental stress through virtual forest therapy (VFT) that restricts the

user’s interaction with various virtual nature environments and stimuli. Nature scenery

exposure could increase positive effects and reduce negative emotions, such as fear or

Forests 2021, 12, 1776

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anger [42]. A further study by [43] found that nature could improve health in four ways:

air quality, physical activity, social interconnection, and stress reduction. Though, a lack of

understanding of the relationship between physiological mechanisms and the quality of

urban green spaces, making stress problems challenging to curb. In today’s technologically

advanced world, where time is a valuable element, green spaces can be brought into the

home using virtual application technology.

This systematic review aims to evaluate the impacts of nature and forest environments

using VR in reducing stress levels. To this end, the proposed systematic review is conducted

to answer the following questions:

1. Is VR effective enough to be employed for mental illness therapy?

2. Are VR environments, including nature and forests, able to mitigate stress levels in

patients? Is there an advantage of using VR technology over nature walks methods?

2. Methods

2.1. Protocol and Registration

This review was performed following the Preferred Reporting Items for Systematic

Reviews and Meta-Analyses (PRISMA) guideline [44], but the review protocol was not

registered in the Prospective Register of Systematic Reviews Platform (PROSPERO).

2.2. Data Sources and Search Strategy

This review was conducted by querying various databases, including Embase, Med-

line/PubMed, Hindawi, ScienceDirect, IEEE, Scopus, Web of Science, and Taylor & Francis.

The screening of titles and abstracts was employed in the ﬁrst phase to determine the rele-

vant articles for this research. Obtained articles were screened again in the second phase

to categorize qualiﬁed articles. The following keywords used are as follows. Apart from

using the term “forest”, another term used in the literature searching correlated to (1) visual

effects (2) nature, and (3) psychological effects. The keywords correlated to (1) visual effects

were “view”, “visual”, and “virtual”; the keywords correlated to (2) nature were “scenery”,

“forest”, “urban park”, “ﬂower”, and “environment”; and the keywords correlated to

(3) psychological effects were “physiological”, “stress”, “heart rate”, and “blood pressure”.

A search range was set within the titles and abstracts and search articles about the human

species to get speciﬁcally related literature from the database. The recent update to the

search was conducted in June 2021.

2.3. Eligibility Criteria

Studies in the collected articles involved participants of various ages ranging from 0

to more than 65. Studies conducted based on less than three participants were excluded,

owing to its irrelevant in the study. VR studies that used the nature of forest therapy or

natural environments were included, while studies that used other types of therapy were

excluded. Additionally, articles that have been published as literature reviews or in other

languages than English were eliminated. The searching for the paper on the databases

began with matching words of “virtual forest”, “virtual scenery”, “virtual urban park”,

“virtual nature”, “virtual plant”, “virtual environment”, “physiological”, “stress”, and

“blood pressure”, which were formed in query strings such as (“virtual forest” and “stress”)

OR (“virtual nature” AND “stress”).

2.4. Study Selection

As shown in Figure 1, 398 papers were found with a duplication of 155 articles. After

screening, 110 articles were excluded because they did not meet the inclusion criteria, did

not use VR devices, or were not published in the last decade from 2013 to June 2021. After

reviewing the titles, 48 related articles remained. After reviewing the abstracts, the full

text of 30 articles was taken for review. After reviewing full-texts, 18 articles matched

the selection criteria. These articles were selected published between 2013 and June 2021

focused on reducing stress using virtual forests.

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Figure 1. Systematic review ﬂow diagram based on the PRISMA.

2.5. Data Extraction

Two independent researchers conducted the search process to ensure a precise and

unbiased process. The following data were retrieved from each study: author (publica-

tion year); country; research design; measurement indicators; outcome variables; and

signiﬁcant ﬁndings.

3. Results

3.1. Search Results

Figure 1 illustrates the ﬂow chart of the systematic review. We collected 398 relevant

papers from the literature containing the above-listed keywords in the titles and abstracts.

A total of 243 publications were found after duplication screening. After title and abstracts

reading, 30 articles were considered eligible. Finally, 18 articles were obtained after a

full-text reading. These articles presented evidence on the impact of forest therapy based

on VR on stressed patients. A paper count was performed to determine the number of

countries with publications concerning nature forest therapy using VR. Figure 2 shows

studies by countries on nature forest therapy using VR. As indicated in Figure 2, China,

Australia, Germany, Sweden, USA, and Japan have the highest publications (two articles)

in the designated journals. Taiwan, Lebanon, Singapore, Korea, Malaysia, and Poland have

published one article.

According to the search results between 2013 and 2016 (four years), only two publica-

tions were made on the nature of forest therapy based on VR. These studies were solely in

2013 and 2014, while no studies were published in 2015 and 2016. This implies that the

concept of using forest therapy based on VR was still in its infancy during these years.

However, since 2017, articles have gradually increased, reaching three articles in 2019, six in

2020, and three in the ﬁrst half of 2021. These statistics in Figure 3 are not unexpected, given

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that VR has lately been widely used in research, particularly in therapy. Additionally, more

research is required to improve people’s well-being and mental health in the workplace

and everyday situations.

Figure 2. The publications of the nature of forest therapy based on VR by country focus.

Figure 3. The annual number of publications on the nature of forest therapy based on VR from 2013

to June 2021.

3.2. Psychosocial and Physiological Effects of Forest Therapy

Recent studies focused on investigating the combined effect of psychological or phys-

iological variables and the external environment on physical and mental health. Earlier

studies on forest therapy concentrated on psychosocial and physiological factors, often

enhancing an individual’s moods (Table 1). Most studies on the psychosocial impacts of

forest therapy used self-report surveys to assess participants’ mood states and overall men-

tal health. Among the most employed methods were the Proﬁle of Mood States (POMS),

positive and negative affect scale (PANAS), visual analogue scales (VAS), standard stress

scale (SSS), perceived stress scale (PSS), and state and trait anxiety inventory (STAI-S).

Along with psychosocial impacts assessment, twelve studies [35,36,45–54] examined the

effects of forest therapy on physiological health by evaluating heart rate (HR), heart rate

variability (HRV), systolic blood pressure (SBP), diastolic blood pressure (DBP), salivary

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amylase (SA), the standard deviation of R-R intervals (SDRR), blood volume pulse (BVP),

and skin conductance levels (SCL).

Four of these studies used POMS and HR/HRV to evaluate the psychological and

physiological responses [46–49]. Tsutsumi, Nogaki, Shimizu, Stone, and Kobayashi [46]

conducted a study to see if stimulation from watching one’s favorite video of the sea or the

forest affected relaxing. Participants were instructed to watch DVDs for sea and forest with

natural sounds for 90 min. The POMS scores were collected on every session, and Bispectral

Index System value and HRV were monitored by the Bispectral Index System and MemCalc

system. Each indication was compared between the two groups of six participants based

on their sea or forest scenery choice. The heart rate, persistent arousal, and high frequency

changed signiﬁcantly as watching the favorite video. These ﬁndings suggested that the

viewer’s favorite movie of the sea or forest had a calming impact. Yu, Lee, and Luo [47]

investigated the physiological and psychological reactions to virtual reality forests and

urban environments. This study used a cross-over and pretest-posttest approach to assess

the VR environment’s impact on forests and urban restoration. The researchers gathered

both physiological and psychological responses (POMS). The ﬁndings revealed that the

subjects’ systolic blood pressure and heart rate reduced over time, regardless of contextual

variables. In simulated urban contexts, an increased degree of weariness and a decreased

level of self-esteem was observed as psychological responses. However, in simulated forest

conditions, vigor levels increased, and negative feelings, such as perplexity, tiredness,

anger-hostility, tension, and despair, decreased. Overall, the beneﬁts of immersing in a

forest environment have proved to be more signiﬁcant. Another study was carried out by

Hong, Joung, Lee, Kim, Kim, and Park [48] to examine the inﬂuence of VR forest video on

adult stress relief using POMS, HRV, and HR measurements. Arithmetic tasks (1-digit by

2-digit numbers multiplication) were used to induce stress in participants before giving

them ﬁve minutes to watch a virtual reality forests (VRF) video. This study revealed that

stress index and HR decreased, conﬁrming that VRF reduces stress in adults, stabilizes

physiological state, and improves psychological state. Wang, Shi, Zhang, and Chiang [49]

presented seven exemplary forest rest areas discovered during ﬁeldwork in Beijing to

participants using VR. Blood pressure, heart rate, salivary amylase, and the Brief POMS

were physiological and psychological indicators, with stress level as the dependent variable.

Each environment type was randomly allocated to 96 participants, and only a kind of forest

resting setting was observed. According to this study, all seven forest rest environments

may reduce stress effects to some level. The impact of different types of forest resting

environments on stress relief is distinct, with the most natural settings having the greatest

impact on stress relief.

Two studies [35,36] used STAI-S as a psychological indicator and HR/HRV or SCL as

physiological indicators. For example, [35] studied the effect of natural noises and stress

recovery in natural surroundings. The study investigated subjective stress (STAI-S) and

physiological recovery (HR) in two virtual natural environments—(1) with exposure to

natural sounds and (2) without exposure to natural sounds—and one control condition

after producing stress with a virtual stress test. The results revealed parasympathetic

activation in the group exposed to natural sounds in a simulated natural environment,

implying increased stress recovery in such settings. The control group and the group

that recovered in virtual nature without sound showed neither autonomic activation

nor inactivation. The ﬁndings imply a possible mechanistic relationship between nature,

natural sounds, and stress recovery, indicating the potential use of VR as a viable method

to manage stress. Li, Sun, Sun, Yuan, and Li [36] investigated the inﬂuence of brightness

levels on stress retrieval when watching VRF with simulated natural light. This study

used pre-test and post-test strategies to examine the effect of different brightness levels

on stress recovery using a virtual forest environment. A total of 120 participants were

recruited to watch stimuli from six immersive virtual environments (IVEs) through a head-

mounted display. The physiological and psychological responses, as well as perceived

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environmental characteristics, were assessed. This study showed that VRF scenes of bright

sunlight reduced stress more effectively than scenes from the dark night.

In two more studies, HR was used with VAS [54] and PANAS [50] to evaluate the

effectiveness of VR in reducing stress. Schebella, Weber, Schultz, and Weinstein [54]

use IVEs comprised of visual, auditory, and olfactory stimuli to examine the impacts

of biodiversity on stress recovery. Their study employed three natural and one urban

environment (none, low, moderate, and high). A further IVE with high biodiversity

was also added, but no auditory or olfactory stimulation. The study reported consistent

reactions to well-being using physiological and self-reported measurements. However,

biodiversity has been shown to have a non-linear effect on stress recovery, and is most

effective in urban settings and most inﬂuential in moderately diverse environments. It

was stated that multisensory (visual, auditory, and olfactory) stimulation improved stress

recovery and did not impact the immersion sense of the participants when compared

to visual-only encounters. In [50], the impact of VR technology on reducing stress and

enhancing individuals’ moods was investigated using a pulse-oximeter and the PANAS.

This study was conducted on 36 women with substance use disorder (SUD) for the ﬁrst

10 min of their daily programs in a residential treatment program for four weeks, including

two activities. A cross-over design was employed to compare seeing natural environments

and performing mindfulness-based activities. As a result, there were statistically signiﬁcant

reductions in mean negative affect ratings and heart rate after seeing a nature scene

and conducting mindfulness-based exercises. Additionally, general mood signiﬁcantly

improved for participants in both circumstances.

The other four studies used other psychological and physiological indicators, such as

EDA and MRJPQ in [45]; GHQ12 and GSR in [51]; POMS, PSS, and GSR in [52]; and PANAS

and SDRR in [53]. For instance, Anderson, Mayer, Fellows, Cowan, Hegel, and Buckey [45]

used VR technology with immersive natural scenery to reduce stress levels and improve

participants’ moods. They recruited 18 participants (9 men and 9 women), aged 32 to 44.

The participants were required to watch three 360◦ views of an indoor control, rural Ireland,

and remote beaches for 15 min. Before the scenes, the subjects were psychologically stressed

with arithmetic tasks. Psychophysiological arousal was measured using EDA and heart rate

variability. The mood and scene qualities were assessed using the positive and negative

affect schedule and the 15-question MRJPQ. When comparing the natural sceneries to the

control scenario, the reductions in EDA from baseline were larger at the end of the natural

scenes. The natural settings reduced negative inﬂuence from baseline, whereas the control

scene did not. The control scene had lower scores of MRJPQ than natural situations. The

preferred scene in the two natural sceneries reduced the negative effect and increased

MRJPQ scores than the second-choice scene. Their study revealed that natural VR could

produce relaxation with the right selection of scenery, owing to its impact on assessing the

mood and quality of the scenery. In [51], VR was integrated with bilateral stimulation for

stress relief to evaluate EMDR. The authors conducted three relaxation training sessions on

28 healthy ofﬁce workers who recorded their subjective stress (GHQ12), HR, mood, GSR,

and muscle response prior to the session. The study revealed a signiﬁcant reduction in

stress levels and improved participant mood using VR based on their ﬁndings. Mostajeran,

Krzikawski, Steinicke, and Kühn [52] studied the effects of exposure to a forest and an

urban virtual environment on mood, stress, physiological responses, and cognition. The

environments were shown as either traditional photo slideshows or 360-degree ﬁlms on a

head-mounted display. Their ﬁndings revealed that the forest environment had a favorable

effect on cognition while the urban environment disrupted mood. Furthermore, images of

an urban or forest setting could lower physiological stimulation than immersive 360-degree

movies. A more recent study by [53], with 111 subjects recruited, highlighted the impact of

buildings with vertical greenery on negative psychophysiological stress responses using

VR technology. The vertical greenery covered the balconies, walls, and pillars of buildings

in the plant state. The plants were replaced with equivalent hues of green in the color

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condition. The study suggested that vertical greenery prevented stress from increasing, as

indicated by heart rate variability.

Two studies measured only physiological responses, such as SCL in [55], and NIRS,

HRV, and SD in [56]. The effects of visual stimuli (virtual 360-degree images of forests,

urban areas, and parks) on recovery from physiological stress have been compared by [55]

to the effect of congruent olfactory stimuli (natural and urban smells) and acoustic stimuli

(birdsong and noise). In their study, a total of 154 participants were randomly assigned

to one of the three situations, urban area, forest, or park, and were then exposed to

stress (operationalized by skin conductance levels). This study showed a signiﬁcant

reduction in stress in parks and forests but not in cities. Igarashi, Yamamoto, Lee, Song,

Ikei, and Miyazaki [56] investigated the physiological effects on relaxation of 3D ﬂoral

pictures compared to 2D images upon prefrontal cortex and autonomic nerve activity.

Ninety male university students, aged 22 to 23, were given 90 s to see the water lily

picture in 3D and 2D images. Their study detected prefrontal cortex (PFC) activity using

near-infrared spectroscopy, whereas autonomic nerve activity was quantiﬁed using HRV.

Besides, a modiﬁed SD approach was used to determine psychological impacts. The 3D

visual stimulation, compared to 2D visual stimulation, resulted in signiﬁcantly decreased

hemoglobin concentration in the right PFC. Additionally, it caused lower sympathetic

activity as measured by the low- and high-frequency ratio of the HRV component and

substantially more realistic feeling, as evidenced by higher SD ratings.

The four ﬁnal research used psychological indicators based on questionnaires and

observations. Moyle, Jones, Dwan, and Petrovich [34] used the observed emotion rating

scale (OERS) to assess the impacts of VRF on dementia patients’ engagement, apathy, and

mood states, and learn more about staff, patients, and their families’ perspectives. Their

study was conducted by the mixed method, consisting of ten individuals with dementia,

ten family members, and nine care professionals from two residential aged care facilities

by one care provider. Residents took part in a VRF session that was facilitated. The results

showed that residents, family members, and staff agreed that the VRF had a favorable

impact. Residents reported signiﬁcantly higher levels of pleasure and attentiveness during

the VRF session. They also felt more fear and anxiety during the forest encounter than the

comparative normative sample. The VRF was considered to have a favorable impact on

dementia patients, although a larger level of fear and anxiety has been observed during

the VRF than the normative sample. Besides, Reese, et al. [57] used SSS and PANAS to

evaluate participants’ condition following the VR experience irrespective of the control.

This study recruited 64 participants who navigated by an experimenter or navigated across

a VR environment. They claimed that lower stress could be experienced through a VR

environment than actively navigating through it.

Scates et al. [58] used a Likert-type scale questionnaire to observe whether a VR

nature could alleviate stress and discomfort in cancer patients in a treatment center. The

authors recruited 50 patients having their regular chemotherapy treatment sessions. These

patients were evaluated for two visits for stress and pain during their intravenous (IV).

They watched a naturally inspired VR simulation during the second visit while getting their

IV. The study found that cancer patients viewing naturally inspired VR were signiﬁcantly

less frustrated, more relaxed, and had peaceful feelings and positive distractions. Besides,

Rozmi, et al. [59] highlighted several design aspects in terms of visual realism, navigation

methods, and aids for users to be fully immersed in the virtual forest environment, thus

reducing their stress levels. The design was based on a game concept and received positive

feedback from users, and the study suggested using elements of nature, such as vegetation,

natural habitat, and forests.

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Table 1. Characteristics of included studies.

References Country

Group

Interventions

Sex (M:F), Age

EG: VR with

EG: 10 (10:0),

nature sounds

age 28.2 ± 10.3.

[35]

Sweden

CG: VR without

CG: 10 (10:0),

nature sounds or No age 28.1 ± 4.4; 10 (10:0),

VR treatment

age 26.7 ± 3.4.

EG: 3D

[56]

Japan

ﬂower images

CG: 2D

ﬂower image

EG & CG: 19 (19:0),

age 22.2 ± 0.6.

EG: natural scenes

(rural Ireland and

[45]

Lebanon remote beaches),

18 (9:9), age 32 ± 12.

and indoor control.

CG: -

EG: nature scence of

[46]

Japan

sea or forest,

and baseline

12 (12:0), age 22.2 ± 1.7.

CG: -

Recovery

Duration

40 min

90 s

15 min

90 min

Aim

Explore physiological

recovery in two

distinct virtual natural

settings, with and

without interaction

with natural sounds.

Evaluate physiological

relaxation effects on

autonomic nerve

activity by viewing 3D

versus 3D

ﬂower images.

Promote nature

exposure for those

living in isolated,

restricted settings.

Evaluate the inﬂuence

on people’s relaxation

while viewing a video

of the sea or a forest.

Outcome

The ﬁndings imply a

possible mechanistic

relationship between

nature, natural sounds,

and stress recovery.

The study found that

realistic 3D ﬂoral

images boost

physiological relaxation

more effectively than

2D ﬂoral images.

VR nature produced

relaxation, and scene

selection had a

substantial impact on

both mood and

visual perception.

The viewer’s favorite

movie of the sea or

forest had a calming

impact. The ﬁndings

also imply that

watching a favorite

scene of a natural

setting could help to

relieve stress

and exhaustion.

Measurement

Technique

STAI-S, HRV,

HR, TWA

NIRS, HRV, SD

EDA,

MRJPQ

POMS, HR, low

frequency, high

frequency, BIS

Results

After the intervention,

signiﬁcant differences

were discovered

between groups (HR,

p = 0.007; TWA,

p < 0.001).

Signiﬁcant differences

were found (NIRS,

p < 0.01; HRV, p < 0.05;

SD, p < 0.01) between

the two groups.

Signiﬁcant differences

were found (EDA,

p = 0.002; MRJPQ,

p < 0.014) between the

natural scenes and

indoor control.

Signiﬁcant stress

reduction was found

(POMS, p < 0.05)

between the nature

scenes (sea and forest)

and their baselines.

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Table 1. Cont.

References Country

[34]

Australia

[47]

Taiwan

[55]

Sweden

Group

Interventions

EG: virtual

reality forest

CG: -

Cross-over study:

forest and urban

VR environments.

Pseudo-randomised

study: VR forest,

park and urban

environments.

Sex (M:F), Age

Residents with dementia:

10 (3:7), age = 89 ± 4.7;

Family members: 10;

Care staff: 9.

30 (13:17), age 20–29.

Forest: 52 (24:28), age 27;

park: 52 (26:22), age 28;

park: 50 (22:28), age 27.

Recovery

Duration

15 min

9 min and 30 s

3 min

Aim

Assess the apathy,

engagement, and

mood of dementia

patients and

to examine employees,

dementia patients, and

family experiences.

Evaluate the effects of

virtual forests on

boosting people’s

psychological

well-being.

Assess the potential for

stress recovery using

three different

environments: urban

areas, parks,

and forests.

Outcome

The VRF positively

affected dementia

patients despite a higher

level of fear/anxiety

during the VRF

compared to the

normative group.

Immersing in forests

could provide beneﬁts

such as reduced

negative emotions and

enhanced vigor as

compared to urban

environments that

lower self-esteem and

raise fatigue levels.

According to the study,

residing in an urban

environment with no

green space, trafﬁc

noise, and tar and diesel

odors can expose people

to a certain amount of

stress compared to

natural environments

such as gardens

and forests.

Measurement

Technique

OERS

PASAT, POMS,

BP, HRV

SCL

Results

Residents reported

higher levels of

happiness (p = 0.008),

attentiveness (p = 0.001),

and anxiety/fear

(p = 0.16).

Signiﬁcant decrease in

negative emotions

(tension, p = 0,

depression, p < 0.017)

observed in

forest environments.

Signiﬁcant differences

were found between

urban areas and both

forest (p = 0.003) and

park (p < 0.001), while

no signiﬁcant

differences (p = 0.39)

between forest

and park.

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References Country

Group

Interventions

Sex (M:F), Age

EG: VR forest,

[48]

Korea

baseline

40 (23:17), age 24.4 ± 2.8.

CG: -

[49]

China

Independent group

design: Pre and

post-VR forests.

96 (33:63),

age 24.03 ± 5.29.

Independent group

design: six

120 (27:93),

[36]

China

immersive virtual

age 19.79 ± 1.90;

environments (IVE)

20 for each scene.

(lightest to darkest).

Table 1. Cont.

Recovery

Duration

5 min

6 min

Aim

Outcome

Evaluate viewing

forest videos in

reducing stress

in adults.

Evaluate stress

recovery after viewing

VR videos of seven

forest environments:

(1) structure, (2) wood,

(3) wood with bench,

(4) wood with platform

and bench, (5) platform

with trees, (6) waterfall

with trees, and (7) pool

with plants.

Investigate how varied

natural light brightness

levels affect people’s

stress recovery effects

in the forest and

provide some proof

for stress

reduction’s mental

well-being beneﬁts.

The study revealed that

watching videos of VR

forests could affect

individuals’ stress

levels, regulate

physiological

conditions, and

positively affect their

mental conditions.

The study investigated

seven forest resting

environments. These

environments showed a

distinct impact on stress

relief and proved to

reduce stress to

some level.

This study conﬁrmed

that bright sunlight

scenes (i.e., the lightest,

lightest, lightest) in the

virtual forest ease

tension more effectively

than the darkest night

sceneries. Another

discovery indicated that

dark settings, such as

sunrise without

sunlight but with a hint

of brightness, had the

same effect.

Measurement

Technique

HRV, HR, SI,

POMS, SD,

PANAS

SBP, DBP, HR,

SA, POMS

SCL, BVP,

STAI-S

Results

Signiﬁcant decrease in

stress was found

(SI, p < 0.01;

HRV, p < 0.05;

HR, p < 0.01;

SD, p < 0.01;

POMS-TMD, p < 0.01).

Signiﬁcant differences

were found in various

environments with

greatest impact in type

6: (SBP, p < 0.01;

DBP, p < 0.05;

HR, p < 0.05;

SA, p < 0.05;

POMS-TMD, p < 0.01)

Signiﬁcant differences

were found in natural

light brightness

(p < 0.001;

SCL, p < 0.001;

BVP, p < 0.001;

STAI-S, p < 0.01).

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References Country

Group

Interventions

Independent group

design: four levels

of biodiversity

[54]

Australia (urban IVE, none;

natural IVE,

low, moderate,

and high).

Repeated measures

design: cancer

patients with/

[58]

USA without viewing VR

during the

intravenous

procedure (IV).

Cross-over study:

nature scene versus

[50]

USA

practicing

mindfulness-based

activities.

[59]

Malaysia Observational study.

Sex (M:F), Age

52 (24:28),

age 37.6 ± 10.6. Not

stated the number of

participants for

each scene.

50 (15:35),

age > 65 (n = 29).

36 (0:36), age ≥ 18.

Public respondents.

Table 1. Cont.

Recovery

Duration

5 min

During IV

procedure for

30 consecutive

days

4 Weeks,

10 min daily

Aim

Evaluate the effects of

biodiversity IVEs on

recovery from

induced stress.

Investigate VR during

IV procedures on

reducing stress and

pain among

cancer patients.

Evaluate the

effectiveness of VR in

reducing stress among

people with SUD.

Use VR nature therapy

as an alternative tool

for stress relief.

Outcome

The ﬁndings revealed

similar well-being

responses across

self-reported and

physiological

measurements,

implying that

biodiversity had an

impact on human

happiness. In the urban

IVE, stress recovery was

the least effective for

most well-being metrics.

The participants felt

signiﬁcantly less

frustrated and more

relaxed while watching

VR nature scenes

throughout intravenous

chemotherapy.

This study provided

preliminary evidence

that nature-viewing had

similar beneﬁts as a

mindfulness therapy for

treating stress and low

mood associated with

recovery from SUD.

An early study found

that VR had potential as

an aid in therapy, with

positive outcomes

from users.

Measurement

Technique

VAS, HR

Likert-type scale

questionnaire

PANAS, HR

Users’ feedback

Results

Signiﬁcant differences

in stress recovery for

subjective stress,

anxiety, and happiness

were found between

urban and low

biodiversity IVEs

(p < 0.05). For HR, no

signiﬁcant differences

were found between the

urban and either

biodiversity IVEs.

Signiﬁcant increases

were found in positive

distractions (p < 0.0001),

relaxation(p < 0.05),

feelings of peace

(p < 0.01).

Signiﬁcant decreases in

mean negative affect

scores (p = 0.001) and

heart rate (p ≤ 0.001)

were found while

viewing nature scenes

and practicing

mindfulness-

based activities.

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References Country

Group

Interventions

Sex (M:F), Age

Cross-over study:

[51]

Poland

VR immersion with

visual, auditory, and

23 (10:13), age 37.2 ± 9.7.

tactile conditions.

Cross-over study:

[52]

Germany forest and urban VR

environments.

34 (23:11),

age 27.26 > 2.14.

EG: VR with active

control and 30-s

[57]

Germany

familiarization

CG: VR with

no control.

EG: 32 (8:24),

age 23.31 ± 4.7.

CG: 32 (9:23),

age 22.7 ± 2.85.

Table 1. Cont.

Recovery

Duration

Aim

Outcome

Measurement

Technique

6.3 min

VR combined with

bilateral stimulation in

EMDR as a

stress-relieving tool.

According to the study’s

preliminary ﬁndings,

VR-based bilateral

stimulation may boost

mood and reduce stress.

GHQ12, GSR

6 min

5 min

Demonstrate the health

and well-being

advantages of natural

environments.

Identify the impact of

control on the positive

effects elicited by

virtual nature

environments.

The forest environment

had a beneﬁcial

inﬂuence on cognition,

while the urban setting

had a negative effect on

mood. Photos of an

urban or forest scene

succeeded better than

360 videos to reduce

physiological arousals.

The study showed that

participants reported

reduced stress, and their

positive affective states

were raised following

the VR experience.

POMS, PSS,

GSR

PANAS, SSS

Results

No signiﬁcant

differences were found

between groups. For

GSR, visual was most

effective in subjective

assessment ofstress

level (pre, 80%;

post, 100%).

Signiﬁcant differences

in participants’ mood

(POMS, p < 0.05;

PSS, no signiﬁcant

effects; GSR, p < 0.001)

Signiﬁcant positive

effect was found after

VR (PANAS, p < 0.001;

SSS, p < 0.001)

Forests 2021, 12, 1776

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Table 1. Cont.

References Country

Group

Interventions

Sex (M:F), Age

Recovery

Duration

Aim

Outcome

Measurement

Technique

Results

Independent group

[53]

Singapore

design: VR based

plant or

color conditions.

111 (40:71),

age 21.63 > 1.81.

5 min

Demonstrate the

inﬂuence emotion and

stress-buffering of

vertical greenery

outside buildings.

The study suggested

that vertical greenery on

city buildings could

help to mitigate

the negative

psychophysiological

effects of stress.

PANAS, SDRR

Signiﬁcant decreases

were observed in SDRR

(p = 0.01)and positive

affect (p < 0.00) in color

conditions. No

signiﬁcant main effect

of the condition

was found.

M: male, F: female, EG: experimental group, CG: control group, SSS: standard stress scale, PANAS: positive and negative affect scale, SDRR: standard deviation of R-R intervals, GSR: galvanic skin response, PSS:

perceived stress scale, GHQ12: general health questionnaire, HR: heart rate, HRV: heart rate variability, VAS: visual analogue scales, BVP: blood volume pulse, SA: salivary amylase, SBP: systolic blood pressure,

DBP: diastolic blood pressure, SI: stress index, SCL: skin conductance levels, BP: blood pressure, PASAT: paced auditory serial addition test, STAI-S: state and trait anxiety inventory, EDA: electrodermal activity,

OERS: observed emotion rating scale, MRJPQ: modiﬁed reality judgment and presence questionnaire, TWA: t-wave amplitude, NIRS: near-infrared spectroscopy, SD: semantic differential, POMS: proﬁle of mood

states, BIS: bispectral index system.

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3.3. Effectiveness of VR Intervention to Relieve Stress

All eighteen studies stated in Table 1 examined the effectiveness of forest VR in

treating physiological and psychological stress. These studies concluded that VR is a

valuable tool for assessing and promoting relaxation among different population groups

and found a statistically substantial reduction in stress levels, except for the study by [51],

who evaluate VR immersion with visual, auditory, and tactile elements. According to

the selected studies, realistic 3D views were found to have a more signiﬁcant inﬂuence

on physiological relaxation than 2D views [56]. Four studies [48,49,57,59] found that

individuals exposed to forest VR experienced a more remarkable improvement in their

stress levels than baseline or before the intervention. Another four studies [47,52,54,55]

compared stress levels in virtual forests with urban areas following the VR intervention,

revealing reduced negative emotions and stress levels in virtual forests. Even vertical

greenery on urban buildings, as claimed by Chan, Qiu, Esposito, and Mai [53], might help

minimize negative psychophysiological impacts of stress.

Additionally, elements of nature, such as sounds [35], were positively correlated

with stress recovery after the VR intervention with sounds than without sounds. Simi-

larly, bright sunlight scenes [36] were more effective in reducing stress than other natural

light brightness levels. The effectiveness of nature was not a monopoly of forests, but

beaches [45] and seas [46] provide similar positive effects to an extent. In health practice,

VR has been proven to mitigate stress among patients with SUD [50], dementia [34], and

cancer, during the intravenous procedure [58].

4. Discussion

This systematic review intended to synthesize existing evidence on the practicality of

VR nature therapy in stress relief. In recent years there has been a growing interest in the

use of VR to simulate natural environments for promoting well-being and health. Eighteen

studies were included in the review. VR has been shown to be a workable and acceptable

means of relieving stress, whereas virtual environments, such as nature or its elements,

improved stress recovery in comparative conditions. The target population groups in the

studies presented in this review covered different age ranges and involved students, cancer

patients, dementia patients, people with SUD, research institute colleagues, organization

workers, social workers, and public members.

The VRF is more operable in practice with better control of the independent factors

and offers a more realistic experience than image or video. The VRF appeared to be used

in health practice. For example, stress research on patients with dementia [34], cancer [58],

and SUD [50] has been respectively conducted, which is a good initiative for further studies

covering more psychological conditions.

Interaction with virtual nature elements, such as sound, lighting, and weather, can

efﬁciently induce recovery for individuals with psychological disorders, including stress

conditions. Various studies have investigated the exposure effect of these natural elements.

Li, Sun, Sun, Yuan, and Li [36] used several brightness levels (i.e., the lightest, lighter,

light), reporting their capability to reduce stress to a certain level. Ref. [35] found a

relationship between nature sounds and stress recovery. Other factors, including weather,

aquatic components, temperature, and humidity, may signiﬁcantly affect physiological and

psychological well-being. However, there are difﬁculties in knowing which elements of

nature have a positive effect on people. More challenging is that individuals’ differences

in responding to these elements can vary depending on the environment in which each

person lives. Although equitable studies are much harder, such parameters have to be

controlled when designing a study.

Further, modern urban design strategies aim to emulate key forest features that are

important in urban settings. Urbanization inevitably reduces the availability of green

spaces, while green spaces generally improve public health and stress recovery. To study

the effects of greenery factors on the psychological condition of the urban population, VR

technologies have been incorporated to design such spaces. Performing a real-world study

Forests 2021, 12, 1776

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that includes vertical greenery on the exteriors of a row of buildings is a challenging task

that requires considerable effort. Field experiments should be conducted to improve the

ecological validity of a study. Based on reviews, greenery factors were a viable variable for

achieving healthy urban environments [53–55]. Urban green spaces can produce cognitive

and psychological advantages by reducing stress [53].

Most studies included in this review conﬁrmed that the effectiveness of VFT in

overcoming methodological barriers in environmental research and demonstrated its

ability to signiﬁcantly improve participants’ health, mood, and ability to recover from

stress. The intervention duration, either short-term < 10 min [36,47–49,51–57,59] or long-

term > 10 min [34,35,45,46,50,58], positively impacted indicators of perceived well-being,

indicating the effectiveness of VRF treatment. According to the reviews, the combination

of nature and sound features in VRF environments has been demonstrated to stimulate

the parasympathetic nervous system and contribute to relaxation, stress restoration, and

behavioral regulation [35]. A more immersive presentation of the VRF could result in more

beneﬁcial natural outcomes, and participants’ preferred views would have the most relax-

ation effect [46]. Thus, experiencing natural virtual surroundings may be a viable solution

to gaining the therapeutic beneﬁts of interaction with real-world nature, particularly for

individuals who are unable to visit real forests or outdoor areas.

The strength of these reviews involved controlling independent factors, enabling

researchers to identify changes in results of VR-based stress therapy using physical and

psychological measures. Limitations included the availability of students and young people

samples, which implies that the results could not be generalized to other age ranges or

those with a lower educational level. Furthermore, some studies were subject to relatively

small sample sizes and various forms of bias [34,45–47,51,56]. For example, the use of

self-reports may lead to a more positive assessment by respondents and the prevalence of

the one-session format may contribute to bias in innovation, as positive assessment may be

related to VR innovation and not to its intervene. Although most studies use both genders

(males and females), few studies have restricted their studies to one gender, which could

be a big limitation. For instance, refs. [35,46] have limited their studies to males only, while

Reynolds et al. have recruited only female participants with SUD. Although using one

group of sex may help to standardize the data and limit the generalizability of studies’

results, the diversiﬁcation of the research group may produce diverse outcomes.

Although the studies discussed above show that VFT holds potential for psychiatric re-

habilitation, there is still a lack of standardization in VR terminology and solutions. A more

consistent approach to VR software architecture would certainly simplify and accelerate

the uptake of VR therapies. This issue may be rectiﬁed shortly, as manufacturers strive to

provide turnkey VR solutions. The programming requirements for creating and developing

virtual environments, on the other hand, may be the most signiﬁcant problem. This is

a signiﬁcant impediment to mainstream adoption, while standardization of VR material

would considerably alleviate the issue, and the situation is improving progressively.

4.1. Direction of Future Studies

Future studies should consider individual social differences and expand to standard-

ized measures and interventions for stress therapy. Long-term studies are crucial for the

efﬁcacy and clariﬁcation of virtual environments. The optimal period of intervention

exposure to guarantee the practicability of VR-based stress therapy remains undetermined,

and, therefore, more robust studies are required. Future studies could examine the psycho-

logical advantages of natural virtual environments in stress therapy by considering various

natural elements. The current review discovered a lack of consistency in viewers’ positions

(standing or sitting) in the studies reviewed, given that standardization of positions could

provide a more accurate evaluation. Additionally, further controlled clinical studies using

VR therapy on ambulatory people with distress, anxiety, post-traumatic stress disorder

(PTSD), depression, and stress-related conditions are needed to enhance coping strategies.

Forests 2021, 12, 1776

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4.2. Strengths and Limitations of the Current Review

This is the ﬁrst review that emphasizes the efﬁcacy and acceptability of VR for nature

therapy of people with stress conditions. The used methodology included search queries

on the digital academic databases and non-indexed references. This method boosted the

number of articles searched and increased conﬁdence that the review’s result integrated all

relevant studies. The search process, including screening, data extraction, and eligibility

assessments, was conducted by two independent researchers to ensure a precise and

unbiased process.

A limitation of the current review is that diversity of applications, target population,

and measurement techniques restricted comparisons between studies. Another limitation

is that the search strategy was conﬁned to databases in English, which may have ruled

out studies in other languages. Reviewed studies used self-report measures, as well as

physiological, psychological, or physical parameters, as no stand-alone metric was used

for measuring stress. Correspondingly, virtual environments aimed at promoting stress

relief were diverse. Therefore, care must be taken when comparing studies and concluding

that natural virtual environments effectively relieve stress.

5. Conclusions

This review provides a narrative synthesis of the literature on VR-based nature therapy

for stress relief. Most studies merged virtual environments with natural elements, such as

sounds, ﬂowers, scenes, light, or vertical greenery on buildings, and all reported a signiﬁ-

cant decrease in stress levels. The current systematic review has limited the generalizability

of the results, and any conclusions should be carefully derived. However, VR is a potential

technology for relieving stress in people. It is a practical and affordable intervention that

allows people to relax at home or work. This may be even more relevant currently, as the

COVID-19 outbreak has caused an increase in stress worldwide.

Author Contributions: Conceptualization, D.R.A.R., S.S., N.D. and F.M.; methodology, E.A., D.R.A.R.

and S.S.; validation, D.R.A.R., S.S., E.A. and S.S.S.A.; investigation, D.R.A.R., S.S., E.A. and S.S.S.A.;

resources, D.R.A.R. and S.S.S.A.; writing—original draft preparation, S.S.S.A.; writing—review and

editing, D.R.A.R., S.S. and E.A.; supervision, D.R.A.R. and S.S.; project administration, D.R.A.R., S.S.

and N.D.; funding acquisition, D.R.A.R. and S.S. All authors have read and agreed to the published

version of the manuscript.

Funding: This research is supported by the Institute of Health Analytics (IHA), Universiti Teknologi

PETRONAS.

Institutional Review Board Statement: Not applicable.

Informed Consent Statement: Not applicable.

Data Availability Statement: Not applicable.

Conﬂicts of Interest: The authors declare no conﬂict of interest.

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