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Original Article 69
http://www.jhr.cphs.chula.ac.th J Health Res
vol.26 no.2 April 2012
THE HARMONIZING EFFECTS OF CITRONELLA OIL
ON MOOD STATES AND BRAIN ACTIVITIES
Winai Sayowan1, Vorasith Siripornpanich2, Teerut Piriyapunyaporn3,
Tapanee Hongratanaworakit4, Naiphinich Kotchabhakdi3, Nijsiri Ruangrungsi1, 5, *
1College of Public Health Sciences, Chulalongkorn University, Bangkok 10330, Thailand
2Research Center for Neuroscience, Institute of Molecular Biosciences, Mahidol University, Salaya, Nakornpathom 73170,
Thailand, 3Salaya Stem Cell Research and Development Project; Research Center for Neuroscience, Mahidol University,
Salaya, Nakhonpathom 73170, Thailand, 4Faculty of Pharmacy, Srinakharinwirot University, Nakhon-nayok 26120, Thailand,
5Faculty of Pharmaceutical Sciences, Chulalongkorn University, Bangkok 10330, Thailand
ABSTRACT: Citronella oil is a famous odor and widely used in mosquito repellent application.
However, the study of the effects of citronella oil on nervous system is rather limited. In this
study we investigated the effects of inhaled citronella oil on emotional states and physiological
parameters of the nervous system. Twenty healthy volunteers participated in this experiment. All
subjects underwent autonomic nervous system recordings. These recordings included:, body
temperature, heart rate, respiratory rate, and blood pressure; mood states were also evaluated as
was electroencephalography (EEG) recording in pre-, during, and post-citronella inhalation The
results were compared with control conditions. These assessments were measured before and
after using a paired t- test statistical procedure. Our results indicated that citronella oil might be
characterized onto the concept of “harmonization”. Citronella significantly decreased blood
pressure, heart rate, and respiratory rate after inhalation. Subjectively, participants reported
feeling in a better mood and fresher. Moreover, the power of alpha and beta brain activities was
increased. These results were then confirmed the stimulating effects harmonized together with
relaxing effect of citronella oil.
Keywords: Cymbopogon nardus Rendle, EEG, alpha power, mood state, autonomic nervous
system
INTRODUCTION
Aromatherapy originated in Europe approximately
5,000 years ago. The practice entailed the use of
essential oils derived from plant extracts to promote
physiological and psychological healing [1].
Traditionally, the essential oils are massaged into
the body, added to bath water, or diffused into the
air. This application is based on the belief that
certain odors promote therapeutic effects ranging
from healing minor skin irritations to altering mood
states [1, 2]. In Thailand, data available from the
Office of Agricultural Economics report a growing
interest in supporting and exporting herbal plants.
In particular kalmegh (Fah-Talay-Jorn) which is
processed into capsule form for the alleviation of
sore throats, aloe vera or medicinal aloe for wound
and burn healing, plai for its relaxing therapeutic
properties, as well as citronella oil as an insect
repellent [3]. Therefore, nowadays there are more
citronella plantations and an increased production
of its oil commercially. This is illustrated by the
fact that the Thai market for citronella oil
production increased significantly from 51.0% in
2007 to 56.8% in 2008 [3].
Citronellal is cultivated in the tropical areas of Asia,
America and South Africa. The citronella grass
* Correspondence to: Nijsiri Ruangrungsi
Tel. +66 (0) 2218 8158; E-mail: nijsiri.r@chula.ac.th
Cymbopogon nardus Rendle, a Poaceae is regarded
as a medicinal plant, but is also widely used as
culinary additive and for perfumery [1]. The
benefits of citronella oil are its antiseptic properties.
The oil is also used as a diuretic, antipyretic, to
induce gastric relaxation in the treatment of irritable
bowel syndrome [4, 5]. The use of citronellal
essential oil has increased over fifty years for its use
as an insect repellent, in particular as a repellent
against mosquitoes, biting flies and fleas. It is found
in many familiar insect repellent products, such as
candles, lotions, gels, sprays, and towelette wipes
[6]. Citronella oil has been registered for its
repellent use in the United States since 1948. The
United States Environmental Protection Agency
considers oil of citronella as a biopesticide with a
non-toxic mode of action [7]. Most research on
citronella oil has focused on its effectiveness as a
mosquito repellent. For example, Ansari found that
after applying citronella lotion for 30 minutes the
number mosquito bites were reduced by 75% [8]
whereas Jaruwichiratana and colleagues also
reported that a 14% citronella cream was effective
against the Culex mosquito under field conditions
for up to one hour which could prevent up to 90%
of mosquito attacks [9]. From the above research
findings and a meta-analysis by Kongkaew and her
colleagues [10] reviewed the effectiveness of
citronella preparations in preventing mosquito bites
70 Original Article
J Health Res
vol.26 no.2 April 2012 http://www.jhr.cphs.chula.ac.th
in laboratory experimental studies. This review
indicated that volunteer olfactory times of different
oil-containing insect repellent products varied. The
sprayed form of the product was spent on olfactory
time lasting at least 20 minutes whereas the cream
products lasted 60 minutes. In addition, mean
protection time of these products was around 82.28
minutes. The review also suggested that after
inhaling the aroma, there were effects influencing
on the nervous system and mood states. In the
nervous system, arousal effects can be broadly
divided into two major forms including cortical
arousal effect which demonstrated by alteration of
brain wave activity and autonomic arousal effect
[11, 12]. For example, massaging rosemary in
healthy volunteers could increase blood pressure
and breathing rate resulting in more attentiveness,
alertness and a cheerful mood state [13], whereas
there was a significant decrease in the power of
alpha wave over the bilateral mid-frontal regions
[14]. These findings suggest that rosemary was
capable of modulating the brain functions. By
contrast, an inhalation of lavender oil caused a
reduction of blood pressure, heart rate and
respiratory rate [15]. These effects were consistent
with Motomura [16] who demonstrated that
lavender can change brain activity with an increase
of theta 1 (3.5-5.5 Hz) and a decrease of beta 1
(13.5-20 Hz) waves.
Accordingly, in the light of these findings it was felt
that citronella oil was worthy of investigation in the
light of the physiological and mood state changes
after the inhalation or other aromatic oils.
In a previous study, the effects of citronella
essential oil on autonomic nervous system activities
and emotional activities were rather limited. The
sedative effect of citronella was confirmed in
experimental animals by Jager [17]. His research
found that under standardized experimental
conditions the motility of female mice was reduced
from 100% for untreated animals to 50.18% by
citronella. In addition, a citronella spray collar
significantly reduced barking in a sample of thirty
dogs [18]. In humans, Saeki and Shiohara
demonstrated vital sign changes after inhaling
citronella. T he R - R interval on the
electrocardiogram was increased, a reduction of
blood pressure and simultaneously with calm and
relaxed emotions [19]. In our present study, we
measured ANS parameters including heart rate,
blood pressure, breathing rate and skin temperature,
as well as CNS detection, first time examining
human brain wave by EEG spectral power analysis
during citronella oil inhalation. The purpose of this
study is to determine the effects of citronella oil in
three dimensions encompassing: the central nervous
system (brain wave), the autonomic nervous system
and the subjective reports of mood states.
METHODS
Subjects
A total of 20 healthy subjects aged between 18 to
29 years (mean 21.40 ±2.76 years) with a body
mass index of 18-25 kg/m2 (mean BMI 20.68 ±
1.89) [20] were enrolled in this study. As a number
of studies have indicated that there are different
brain activities in the left-handed and right-handed
subjects during olfactory tasks. Accordingly, only
right handed participants were tested. Handedness
was tested using Edinburgh Handedness Inventory
scale [21]. The subjects were then screened for a
normal sense of smell by the n-butyl alcohol test
[22]. Personal health status was also recorded;
including weight, height and blood pressure.
Subjects with symptoms of upper respiratory tract
infection, neurological or psychiatric disorders,
hypertension, cardiovascular diseases or a history of
smoking were excluded from this study [23]. In
addition, female who were menstruating on the day
of testing were also excluded [24]. In addition to the
exclusion criteria outlined above all participants
were given routine information for subjects
preparing for a EEG recording, such as they were
not allowed to apply any sprays, antiperspirants or
perfumes to their hair twelve hours prior to testing.
All subjects were advised not to be fatigued or
drowsy at the start of the experiment.
The present study was approved by the Ethical
Review Committee for Research Involving Human
Research Subjects, Health Science Group,
Chulalongkorn University. The study was approved
and given the Permissions no. COA NO.009/2011.
Informed consents explaining all aspects of the
study were given to participants and were handed
out for the subjects to read and sign. The subjects
were told that they had the rights to withdraw at any
time.
Essential oil administration
The citronella oil was obtained from the Thai China
Flavors and Fragrances Company. The composition
was analyzed by gas chromatography/mass
spectrometry (GC/MS) equipped with Finnigan
DSQ MS detector, Thermo Finnigan model Trace
GC Ultra. Identification of the oil’s constituents
was achieved by matching their mass spectra and
retention times, indicated in NIST05 MS library;
the percentage compositions also were computed
from GC peak area. The result revealed that
citronella oil consisted of three main kinds on α–
citronellal 33.22%, geraniol 21.12% and citronellol
13.07%. One milliliter of sweet almond oil, the base
oil, or 10% v/v citronella oil, diluted in base oil,
was delivered using an oxygen pump system
through plastic tube via respiratory masks in
inhalation set for adults that permits selective
airflow (2 liter/min). According to previous studies,
Original Article 71
http://www.jhr.cphs.chula.ac.th J Health Res
vol.26 no.2 April 2012
it has been found that the pleasantness of the oil
smell could induce an autonomic variability [25,
26]. Therefore, the subjects were asked to inhale
base oil and citronella oil and then rated the level of
pleasantness on a 5-point Likert scale before
starting the experiment. The subjects who rated the
pleasantness of the oil within 2-4 point were
allowed to proceed in the experiment.
Autonomic Nervous System (ANS) and mood
measurement
Simultaneously, mood state and ANS parameters
(e.g. blood pressure, heart rate, skin temperature
and respiratory rate) were recording using the life
scope 8 bedside monitor (Nihon Kohden, Japan) for
ANS parameters, while mood state was rated by the
Geneva Emotion and Odor Scale (GEOS) [27]. This
particular scale is consisted of a 100 millimeters,
monopolar visual analog scale following by 5
factors: pleasant (good), unpleasant (bad,
uncomfortable, disgusted, frustrated and/or stressful),
sensual (romantic), relaxed (serene, drowsy), and
refreshing (energetic).
Procedure
To reduce circadian variation, all experiments were
conducted in the morning (8-12 am) and done in the
silent room with an ambient temperature of 24±1 ºC
and 40-50% humidity. Prior to the experiment, the
subjects would be inquired whether they had any
olfactory problems – none did. After they sat
comfortably in the adjustable armchair, the ANS
electrodes were then attached to suitable positions.
The researcher monitored ANS parameters (e.g.,
heart rate, skin temperature and respiratory rate)
every 1 minute; systolic and diastolic blood
pressure every 5 minutes. Three sections of this
examination, including the first part was served as a
base line trial (resting period), taking approximately
10 minutes. Later the second and third trials, they
took 20 minutes each. Sweet almond oil was
administered in the second trial, whereas 10% v/v
citronella oil diluted in sweet almond oil was
applied to the third trial. The researcher required the
subject to subjectively rate their mood state on a
scale at the end of the first trial, the procedure was
also repeated in the second and third trials.
EEG recording
A set of 31 electrodes with 1 additional ground
electrode were placed onto the subject’s head
according to the international 10-20 system at FP1,
FP2,FZ, F3, F4, F7, F8, FT7, FC3, FCZ, FC4, FT8,
T3, T4, T5, T6, TP7, TP8, C3, CP3, C4, CZ, CPZ,
CP4, P3, P4, PZ, O1, O2 and OZ. Two mastoids
were used as a recording reference (average of both
mastoids, Al + A2/2). The electro-oculogram
(EOG) was measured by placing 4 electrodes in
two external acanthi (HEOL and HEOR), left
supraorbital (VEOU) and infraorbital (VEOL)
regions. Electro-Cap is made of an elastic spandex-
type fabric with recessed silver/silver chloride
(Ag/AgCl) electrodes attached to the fabric.
Electrode impedances were adjusted to below 5
kOhms. Acquire Neuroscan version 4.3 (Neurosoft,
INC) used as recording system. An online filter was
set to band pass; with low frequency of 70 Hz and
high frequency of DC. A/D rate was 500 Hz and the
gain was set at 19. Notch filter was open at 50 Hz
[28, 29]. The relative power spectrum of the
respective frequency bands derived by Fast Fourier
Transformation (FFT) was expressed as follows:
Delta (0-3.99 Hz), Theta (4-7.99 Hz), Alpha1 or low
frequency alpha (8-10.99 Hz), Alpha2 or high
frequency alpha (11-12.99 Hz) and Beta (13-29.99
Hz) wave ranges. The studied areas were divided into
the left anterior (Fp1, F3, F7), right anterior (Fp2, F4,
F8), right posterior (P4, T6, O2), left posterior (P3,
T5, O1), and middle (Fcz, Cz, Cpz) [30].
EEG experimental conditions were identical to
those of ANS experiment. The procedure was
divided into 4 sessions of 7-min each. Baseline
EEG recording was done in both eyes-close and
eyes-open sessions. The participants were then
exposed to undiluted sweet almond oil and lastly
10% v/v citronella oil diluted in sweet almond oil.
DATA AND STATISTIC ANALYSIS
The SPSS statistical package 16 was used for data
analysis on the effects of citronella on physiological
and mood states in two steps (before and after)
treatments. A paired t-test was carried out on the
data concerning blood pressure, heart rate, skin
temperature, and respiratory rate as well as power
of brain wave and rating of mood state.
RESULS
Autonomic Nervous System parameters
The mean and standard derivation (SD) values of
the ANS parameters in the experiment are shown in
Table 1. The data on various ANS parameters were
compared during resting, sweet almond oil and
citronella oil inhalation Our results showed
significantly decreased heart rate (p-value <0.05)
during the sweet almond oil treatment compared
with those of resting. When subjects inhaled
citronella, the blood pressure, heart rate and
respiratory rate were significantly decreased
compared with sweet almond oil inhalation. The
skin temperature, on the contrary, was not
significantly changed.
Mood state response
The mean and SD values of mood state response are
shown in Table 2. After a citronella inhalation,
subjects felt that they had significant increases in
pleasant emotions; good, fresh, relaxed and calm
feelings (p-value <0.05). No significant change was
observed in the case of other mood states (p-value >
0.05, data not shown).
72 Original Article
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vol.26 no.2 April 2012 http://www.jhr.cphs.chula.ac.th
Table 1 Mean and SD values of ANS parameter change during resting, sweet almond oil and citronella inhalation.
Parameters
(n=20)
Rest
Sweet almond oil
Citronella
p-value
rest and SO
p-value
SO and CI
Mean ± SD
Mean ± SD
Mean ± SD
Systolic Blood Pressure
105.42 ± 7.61
105.07 ± 7.89
103.36 ± 7.60
0.764
0.001*
Diastolic Blood Pressure
64.17 ± 8.88
63.62 ± 7.86
62.48 ± 7.70
0.757
0.021*
Heart Rate
70.84 ± 13.74
69.04 ± 11.98
66.61 ± 12.01
0.006*
0.000*
Skin Temperature
31.19 ± 2.37
31.58 ± 2.17
31.47 ± 2.40
0.118
0.312
Respiratory rate
16.29 ± 2.85
15.58 ± 3.26
14.76 ± 3.07
0.067
0.003*
* Significant difference, p-value < 0.05
SO = Sweet almond oil, CI = Citronella oil
Table 2 Mean and SD values of emotional state changes during resting, sweet almond oil and citronella oil inhalation.
Emotion
(n=20)
Rest
SO
CI
p-value
rest and SO
p-value
SO and CI
Mean
SD
Mean
SD
Mean
SD
Good
54.75
16.66
57.40
17.92
68.90
20.97
0.516
0.004*
Fresh
48.30
22.46
47.35
17.10
54.25
14.67
0.850
0.040*
Relaxed
52.20
23.80
50.85
22.38
71.15
16.24
0.804
0.002*
Calm
46.45
26.97
52.85
24.95
65.85
17.50
0.229
0.048*
* Significant difference, p-value < 0.05
SO = Sweet almond oil, CI = Citronella oil
Table 3 Mean brain waves’ power during eyes closed, sweet almond oil and citronella oil inhalation.
Brain area
EC
SO
CI
p-value
EC and SO
p-value
SO and CI
Alpha1 Power (8-10.99 Hz) (µV2)
left anterior
8.31
7.71
8.93
0.140
0.093
right anterior
9.10
8.44
10.19
0.177
0.016*
Center
12.66
11.62
14.17
0.202
0.012*
left posterior
9.42
9.26
12.57
0.762
0.002*
right posterior
10.76
10.68
14.52
0.921
0.003*
Alpha2 Power (11-12.99 Hz) (µV2)
left anterior
2.59
2.51
2.79
0.462
0.279
right anterior
2.68
2.59
2.97
0.446
0.142
Center
3.95
3.74
4.52
0.328
0.029*
left posterior
4.54
4.70
5.52
0.457
0.006*
right posterior
6.79
7.16
7.97
0.227
0.153
Beta Power (13-30Hz) (µV2)
left anterior
0.28
0.28
0.31
0.890
0.032*
right anterior
0.29
0.30
0.33
0.930
0.093
Center
0.37
0.36
0.43
0.878
0.003*
left posterior
0.32
0.32
0.39
0.944
0.000*
right posterior
0.35
0.36
0.42
0.860
0.000*
* Significant difference, p-value < 0.05
EC = Eyes closed session, SO = Sweet almond oil, CI = Citronella oil
EEG data
The EEG power was calculated for each frequency
band among resting, sweet almond oil and citronella
oil inhalation. Our results revealed power changing
of each brain wave frequency during three
experimental sessions (Table 3) and expressed by
topographic maps in Figure 1. There were
noticeable changes of band power in alpha1 waves
that significantly increased during the citronella
inhalation in all brains areas (p-value <0.05), except
for left anterior (p-value =0.093). Conversely, the
power of alpha2 waves were significantly increased
in central (p-value =0.029) and left posterior
(p-value =0.006) brain areas. Furthermore, beta wave
power was also increased in all brain areas during
citronella oil inhalation, except for right anterior
brain region. However, no significant change was
observed in the case of theta wave power (p-value >
0.05, data not shown). In Figure 1, the topographic
map shows after inhaling citronella compared with
resting and sweet almond oil inhalation. The alpha1
wave power increased obviously in bilateral temporal
and central areas whereas the power of alpha2 wave
increased mainly in posterior brain area. In addition,
an increase of beta wave power was observed in
anterior and posterior parts of the brain.
Original Article 73
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vol.26 no.2 April 2012
Brain topography
Alpha1 Eyes closed
Alpha1 Sweet almond oil
Alpha1 Citronella
Alpha2 Eyes closed
Alpha2 Sweet almond oil
Alpha2 Citronella
Beta Eyes Close
Beta Sweet almond oil
Beta Citronella
Figure 1 Brain Topographical map of the distribution of alpha and beta wave activities. The red areas indicate a higher
power of brain wave in each frequency
DISCUSSION
In the present study, citronella oil was administered
by inhalation to healthy subjects. Brain wave
activity and ANS parameters, such as blood
pressure, heart rate, respiratory rate and skin
temperature, were recorded as indicators of the
arousal level of nervous system. In addition,
subjects had to subjectively rate their mood state in
terms of good, bad, active, drowsy, fresh, relaxed,
stressed, uncomfortable, romantic, frustrated, calm,
and disgusted in order to assess subjective
behavioral arousal.
The results of this study support previous studies
indicating citronella balancing effect. The observed
effects of citronella are not precisely characterized
by concept like stimulant or relaxation since
inhalation of citronella oil significantly decreased
the level of ANS arousal shown by a reduction in
blood pressure, heart rate and respiratory rate. This
finding is consistent with those reported by Saeki
and Shiohara [19]. The power of alpha1 (8-10.99
Hz), alpha2 (11-12.99 Hz) and beta (13-30 Hz)
activities were significantly increased. Since several
reports had demonstrated the effects of citronella on
physiological responses. Our finding also suggests
an apparent influence on main component. After
analyzing by GCMS, there were main components
citronella is citronellal, geranoil and citronellol
which a monoterpene. Various studies have shown
that monoterpines and their derivative compounds
also exhibit several types of pharmacological
properties, such as antinociception, antidepressant
and sedative effects [31]. In citronellal, previous
studies found mice treated with citronellal presented
behavioral alterations such as decrease of
spontaneous activity, ataxia and sedation. [32, 33].
Furthermore, Azarmi and colleagues found that the
vascular effect of geraniol, other main components
of citronella oil. Geraniol was able to reduce the
contractile response to noradrenalin in vascular
walls and heart leading to a further rate of aorta
relaxation with lower blood pressure and lower
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heart rate [34]. In comparison with other volatile
oils comprising similar components as those of
citronella, such as rose oil (Rosa Damascena Mill)
having main components of geraniol and
citronellol, such as after applying rose oil to the
abdomens of forty healthy subjects a significant
decrease of breathing rate, blood oxygen saturation
and systolic blood pressure as well as more calm,
more relaxed and less alert was observed than the
subjects in the control group. After applying rose
oil on 40 healthy participants’ abdominal surface,
the subjects from the study group revealed
decreases of breathing rate, blood oxygen saturation
and systolic blood pressure, and more calm mental
state, the felt more relaxed and less alert than
subjects in the control group [35]. Furthermore,
Khyaudeen indicated that thirty subjects who
inhaled rose oil for fifteen minutes had a significant
reduction of blood pressure and feeling more
relaxed. In EEG reports, rose oil significantly
decreased beta wave power but increased alpha
wave power [36]. These findings were similar to
our results in terms of alpha wave power increment
but were different to the beta wave power changes
after citronella inhalation. The significant increase
in power of beta wave may relate to high arousal
levels. For example, the Sugnano study found the
healthy participants had more brain beta wave
activity and felt fresher after jasmine oil inhalation
[37]. Thus, this study supported that citronella
inhalation induced a significant increase in
relaxation and fresh feelings in participants.
Overall, the changes observed could be interpreted
as reflecting the harmonious status of arousal and
relaxation, the so-called “relaxed concentrate”.
Similar changes have been reported in other studies.
For example, Hongrattaworakit tested the effects of
Ylang-Ylang oil and its effect characterized by the
concept of “harmonization”. They found that after
the oil inhalation induced a decrease in blood
pressure and pulse rate, an increase in subjective
emotions, including feelings of attentiveness and
alertness [38]. Similarly, Morinush studied the
combination effect of peppermint oil and eucalyptus
oil resulted in similar findings [39]. In short, these
results were possibly relevant in individually
increasing the cognitive and mental relaxation
effects as evidenced by the increase of alpha and
beta brain powers.
CONCLUSION
In conclusion, our study explored the effects of
inhaled citronella oil on the CNS and other psycho-
physiological changes. Our findings support the
influence of citronella oil on brain wave activity,
autonomic nervous system response and mood
states, which emphasizes the effects of citronella
harmonization.
ACKNOWLEDGEMENTS
The authors wish to thank The 90th Anniversary of
Chulalongkorn University Fund (Ratchadaphisek-
somphot Endowment Fund) and Herbal Remedies
and Alternative Medicine Task Force of STAR:
Special Task Force for Activating Research under
100 years Chulalongkorn University fund for their
research grant and support for this study. The
authors are grateful to Dr. Chanida Palanuvej and
Miss Thidarat Duangyod for the GCMS protocol
they recommended.
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