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Abstract

The effects of aromas on humans are divided into physiological and psychological effects. The physiological effect acts directly on the physical organism, the psychological effect acts via the sense of smell or olfactory system, which in turn may cause a physiological effect. This paper reviews on the physiological effects which are used for the evaluation of the effects of aromas. Physiological parameters, i.e. heart rate blood pressure, electrodermal activity, electroencephalogram, slow potential brain waves (contingent negativevariation), and eye blink rate or pupil functions, are used as indices for the measurement of the aroma effects
REVIEW ARTICLE
Physiological effects in aromatherapy
Tapanee Hongratanaworakit
Abstract
Hongratanaworakit, T.
Physiological effects in aromatherapy
Songklanakarin J. Sci. Technol., 2004, 26(1) : 117-125
The effects of aromas on humans are divided into physiological and psychological effects. The physi-
ological effect acts directly on the physical organism, the psychological effect acts via the sense of smell or
olfactory system, which in turn may cause a physiological effect. This paper reviews on the physiological
effects which are used for the evaluation of the effects of aromas. Physiological parameters, i.e. heart rate
blood pressure, electrodermal activity, electroencephalogram, slow potential brain waves (contingent nega-
tive variation), and eye blink rate or pupil functions, are used as indices for the measurement of the aroma
effects
Key words : aromatherapy, physiological effects
Dr.rer.nat. (Pharmacy), Department of Pharmaceutical Chemistry, Faculty of Pharmacy, Srinakharinwirot
University, Rangsit-Ongkharak Road, Nakhon Nayok 26120, Thailand.
Corresponding e-mail: tapanee@swu.ac.th
Received, 9 June 2003 Accept, 17 October 2003
Physiological effects in aromatherapy
Hongratanaworakit, T.
Songklanakarin J. Sci. Technol.
Vol. 26 No. 1 Jan.-Feb. 2004 118
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ing. Moreover, it is too early to classify essences
or aromas according to their action on the physical
organisms because there is very little detailed re-
search on the effects of aromas. Thus, this paper
reviews selected experimental research on the
physiological effects and describes how they may
exert therapeutic effects in aromatherapy. The aims
of this paper are: (i) to alert aromatherapists on the
scientific background underlying potential thera-
peutic uses of aromas (ii) to encourage the clinical
evaluation of aromas.
Physiological effects
Physiological effects of aromas can be di-
vided into two types: those which act via the stimu-
lation of the nervous system and those which act
directly on an organ or tissue via an effector-
receptor-mechanism (Tisserand, 1977). The physi-
ological measures are all under the control of the
nervous system. In general, the nervous system of
higher organisms can be classified into two major
sections, the central nervous system (CNS) and the
peripheral nervous system. The CNS includes the
brain and spinal cord. Two important functions of
the CNS are to receive and process sensory infor-
mation and to regulate bodily movements. The pe-
ripheral nervous system refers to the nervous tis-
sues outside the brain and spinal cord, including
the cranial and spinal nerves. The peripheral nerv-
Clinical experience in aromatherapy suggests
that beneficial effects of aromas or fragrances are
not only exerted by inhalation of the vapor but also
by absorption of fragrance molecules through the
skin. It is long known that inhalation of aromas
causes physiological and psychological changes in
humans (Tisserand, 1977) and it is assumed that
the effects of aromas are evoked by both pharma-
cological and psychological mechanisms. The
former acts directly on the physical organism, the
latter acts via the sense of smell and may thereby
elicit physiological effects. The physiological and
psychological effects are quite distinct although
they often occur simultaneously (Jellinek, 1997).
In order to study effects of fragrances researchers
have taken a great variety of approaches including
measuring changes in the patterns of electromag-
netic activity in the brain, in physiological param-
eters, e.g. heart rate, electrodermal activity, blood
pressure, muscle tension, skin temperature, and skin
conductance (Van Toller et al., 1983; Kanamura et
al., 1988; Lorig et al., 1988; Torii et al., 1988; Lorig,
1989; Miyazaki et al., 1991; Buchbauer et al., 1993;
Van Toller et al., 1993; Brauchli et al., 1995).
However, to date, reported results of the ef-
fects of aromas have been unclear. Many aromas
seem to have both stimulating and sedative proper-
ties. Therefore, to classify odors as simply ‘stimu-
lant’ or ‘sedative’ can be misleading and confus-
Physiological effects in aromatherapy
Hongratanaworakit, T.
Songklanakarin J. Sci. Technol.
Vol. 26 No. 1 Jan.-Feb. 2004 119
ous system is further divided into the somatic nerv-
ous system, concerned with muscular activities, and
the autonomic nervous system (ANS) which con-
trols visceral structures (glands and organs of body).
In addition, the function of the ANS is to regulate
the internal and relatively involuntary responses that
are associated with emotions. Finally, the ANS is
subdivided into the sympathetic nervous system
(SNS) and the parasympathetic nervous system
(PNS). These two branches differ in functions. The
SNS is dominant in situations requiring mobiliza-
tion of energy whereas the PNS is dominant in a
rest situation. Some organs are innervated by only
one division of the ANS (e.g., the sweat glands,
peripheral blood vessels, and adrenal glands are
innervated solely by the SNS). Most organs are in-
nervated by both the SNS and the PNS. In those
cases, the SNS and the PNS branches usually pro-
duce opposite reactions. Among the most signifi-
cant of the bodily reactions produced by the SNS
are pupil dilation, inhibition of salivation (causing
a dry mouth), secretion of sweat (causing clammy
hands), constriction of blood vessels in the periph-
ery of the body (causing cold hands and feet), dila-
tion of blood vessels in the muscles and brain, in-
crease of heart rate, increase of blood pressure,
speeding of breathing rate, and inhibition of diges-
tive processes. Among the bodily reactions pro-
duced by the PNS are pupil constriction, increase
of salivation, decrease of heart rate, decrease of
blood pressure, decrease of breathing rate and in-
crease of digestion and peristaltic processes
(Andreassi, 2000).
Evaluation of the effects of aromas on the
nervous system may be divided into two different
forms of arousal, the cortical arousal such as brain
wave activity and the autonomic arousal such as
heart rate, skin conductance. Decreases of the cor-
tical arousal and/or the autonomic arousal are in-
terpreted in terms of a sedative/relaxing effect of
aromas. In contrast, increases of the cortical arousal
and/or the autonomic arousal are interpreted in
terms of a stimulating effect of aromas (Stern et
al., 2001). The changes of physiological parameters
in response to aromas are reviewed throughout this
paper. They are heart rate, blood pressure, electro-
dermal activity, electroencephalogram (EEG), con-
tingent negative variation (CNV), and eye blink rate
or pupil functions.
Effect of aromas on heart rate
The most common psychophysiological
measure of heart activity is heart rate. Faster heart
rate is often caused by stress, for example, our heart
may race and pound when we are afraid. Other kinds
of stress, such as depression, may result in lower
heart rate. Generally, the heart is innervated by the
ANS. The PNS reduces the activities of the heart
and particularly influences heart rate, whereas the
SNS increases the activities of the heart and par-
ticularly affects the pumping function.
A study conducted at Yale University
(Schwartz et al., 1988) used changes of heart rate
and blood pressure as indices for the measurement
of the sedative effects of aromas. The aroma of
spiced apple possesses pronounced vasodepressor
and stress reduction effects. Yamaguchi (1990) also
used the changes of heart rate for the measurement
of effects of lemon and rose aromas. Lemon aroma
caused an increase of heart rate whereas rose aroma
led to a decrease of heart rate. This finding likely
indicates that lemon aroma possesses a stimulating
effect (an increase of heart rate), in contrast, rose
aroma possesses a sedative effect (a decrease of
heart rate). In a similar investigation of Kikuchi
and co-worker (1991), lemon aroma enhanced the
deceleration of the heart rate, indicating a stimu-
lating effect. On the other hand, rose aroma sup-
pressed it which is likely represented a sedative
effect. In the same year, Nagai et al. showed that
sweet fennel oil suppressed the deceleration of heart
rate as well. Brauchli et al. (1995) reported that a
pleasant and an unpleasant odor presentation af-
fected an autonomic variable, i.e. heart rate. An
increase of heart rate was observed during valeric
acid presentation. In contrast, a decrease of heart
rate was found during phenylethyl alcohol presen-
tation. Phenylethyl alcohol was rated pleasant,
while valeric acid was judged unpleasant. Recently,
Hongratanaworakit et al. (2003b) investigated the
Physiological effects in aromatherapy
Hongratanaworakit, T.
Songklanakarin J. Sci. Technol.
Vol. 26 No. 1 Jan.-Feb. 2004 120
effects of sweet orange aroma on human behavior
and detected changes of heart rate in response to
olfactory stimulation. They reported that sweet or-
ange aroma caused significant increases of heart
rate and subjective alertness after inhalation. These
findings seemed to show a stimulating effect of
sweet orange oil. Thus the pattern of changes in
the heart rate reveal differences between stimulant
aromas and sedative aromas.
Effect of aromas on blood pressure
Blood pressure is one of the most frequently
measured physiological variables. It is used as a
general index of cardiovascular function and health.
The maximal, or systolic blood pressure occurs
when the ventricle of the heart contracts. Follow-
ing the period of cardiac contraction, there is re-
laxation of the ventricle, during which blood pres-
sure is at a minimum; a measurement at this time
yields diastolic blood pressure. Blood pressure is
regulated by various factors such as blood volume,
peripheral resistance. In general, diastolic blood
pressure varies mostly with peripheral resistance,
whereas systolic blood pressure is related to both
peripheral resistance and stroke volume. Blood
volume is much less familiar than blood pressure.
It refers to the amount of blood that is present in a
certain portion of body tissue at a given time. If
blood volume is low, then blood pressure is reduced.
The more blood is pumped by the heart and the
more blood vessels constrict, the higher the blood
pressure. All of the blood vessels of the body, ex-
cept the capillaries, are innervated by nerve fibers
from the SNS alone (Andreassi, 2000). This is con-
trolled via the vasomotor center, which is located
in the reticular substance of the brain (lower pons
and upper medulla). The hypothalamus of the brain
can exert powerful inhibitory or excitatory effects
on the vasomotor center. Thus, blood pressure was
recorded as an indicator of the arousal level.
Warren et al. (1987) patented the use of a
nutmeg-based aroma to reduce stress in humans as
measured by the reduction in blood pressure and
self-ratings. Subjects were stressed by mental arith-
metic and sentence completion tasks under an
aroma with and without nutmeg oil. This study re-
vealed that nutmeg oil reduced systolic blood pres-
sure by 9 mmHg. In addition, subjects rate them-
selves as having increased calmness and happiness
as well as decreased anxiety, anger and embarrass-
ment. These effects may be due to myristicin and
elemicin, two ingredients of nutmeg oil which con-
vert to the mood-alerting hallucinogens trimethoxy-
amphetamine (TMA) and methoxy-methylene-
dioxy-amphetamine (MMDA). As in the European
Patent (1991), the odorants, i.e. nutmeg oil, neroli
oil, valerian oil, mace extract, myristicin, elemicin
and isoelemcin, were investigated. When these
odorants were used in a perfume compound at ap-
propriate levels, a significant decrease of systolic
blood pressure has been found. A study conducted
at the Royal Sussex County Hospital (Woolfson et
al., 1992) showed that foot massage with essential
oil of lavender lowered blood pressure as well as
heart and respiratory rates of the patients in an
intensive care unit. Transdermal absorption of
sandalwood oil and one of its main components,
α-santalol led to a trend towards a larger decrease
of systolic blood pressure as compared to the pla-
cebo group (Hongratanaworakit et al., 2003a).
Furthermore, effects of chiral fragrances on human
blood pressure and self-evaluation were explored
by Heuberger et al. (2001). In their studies, chiral
fragrances (enantiomers of limonene and carvone)
caused increases of blood pressure, subjective rest-
lessness and alertness. These findings are likely to
represent a stimulating effect of these fragrances.
Recently, Hongratanaworakit et al. (2002) have
demonstrated that ylang-ylang oil exhibited a har-
monizing effect. Inhalation of the ylang-ylang oil
led to a decrease of blood pressure and an increase
of subjective attention. In addition, transdermal
absorption of the mixed oil of bergamot oil and lav-
ender oil caused a significant decrease of blood
pressure. This finding points towards a decrease
of autonomic arousal (Hongratanaworakit et al.,
2003c).
Effect of aromas on electrodermal activity
The electric conductance of the skin is one
of the most widely used indices of the level of
arousal. It was observed that most people are
Physiological effects in aromatherapy
Hongratanaworakit, T.
Songklanakarin J. Sci. Technol.
Vol. 26 No. 1 Jan.-Feb. 2004 121
familiar with having cold, clammy hands under
stressful circumstances, such as meeting new peo-
ple or having to perform in front of an audience.
The coldness comes from constriction of the smooth
muscles surrounding the blood vessels, while the
dampness is caused by the sweat gland activity. The
sweat glands secrete a salty solution in response to
emotional and stress stimuli, and this salty solu-
tion conducts electricity. Therefore it would seem
plausible that this electric conductance property is
closely associated with psychological processes
such as attention and emotion (Edelberg, 1972;
Fowles, 1973; Lykken et al., 1971; Prokasy et al.,
1973). It is now accepted that changes in the skin
conductance represent changes in the sweat gland
activity. These are mediated by cholinergic sym-
pathetic fibers (Lader et al., 1980). Sweat glands
are innervated solely by the SNS division and there-
fore electrodermal measures are useful indicators
of the SNS activity during emotional states. The
SNS activity is associated with increased sweat
gland activity and this activity in turn is associated
with high skin conductance.
Parasuraman et al. (1992) reported that pe-
riodic half-minute bursts of peppermint aroma dur-
ing a vigilance task increased skin conductance.
In addition, Steiner (1994) studied the effects of
rose and jasmine aromas by using skin conduct-
ance as an indicator of arousal. The interesting find-
ings showed that electrodermal activity of the syn-
thetic rose and jasmine aromas indicated much
lower arousal effect than those of the correspond-
ing natural products. This is important because, in
many of the reported studies on the effects of these
aromas, it is not clearly indicated whether the sam-
ple employed was synthetic or natural. Since the
natural aromas are more expensive than the syn-
thetic ones, the synthetic ones are more likely to be
used in some cases. Bergamot oil, lavender oil and
a 2:1 mixture of the two were also tested in this
study. When the electrodermal activity and the sub-
jective measures of the activation were explored,
the mixture ranked lower arousal effects than ei-
ther of the single ones. This point seemed to raise
the danger in assuming a combination of the physi-
ological effects in the case of mixtures. The effects
of odors on autonomic activity (skin conductance
level) were studied by Brauchli et al. (1995). 2-
Phenylethanol, a widely used as a fragrance simi-
lar to the odor of roses, showed a decrease of skin
conductance level and was rated as a pleasant odor.
On the other hand, pentanoic acid, an odor related
to sweat or cheese, showed an increase of skin con-
ductance level and was judged as an unpleasant
odor.
Effect of aromas on electroencephalogram
(EEG)
The effects of aromas are evaluated by elec-
troencephalogram (EEG). EEG measurements
show brain wave responses expressed in brain wave
amplitude and frequency. Aromas produce cortical
brain wave activity responses involving alpha, beta,
delta, and theta waves. Brain waves are known to
vary with extreme sensitivity according to the level
of consciousness of the subject. Brain waves are
distinguished by their frequency. The waves with
8-13 Hz are called alpha wave, those with higher
frequency beta wave, and those with lower fre-
quency theta and delta waves. When engaged in
reading or concentrated thought, or in highly emo-
tional, or other tense mental states, beta wave is
dominant and alpha wave is inhibited. On the other
hand, alpha wave is dominant in mentally relaxed
state. Thus, brain waves are faithfully reflect hu-
man levels of consciousness, psychological state
and degree of arousal.
Lorig and Schwartz (1988) recorded the
brain waves of subjects exposed to the four types
of aromas, i.e., eucalyptus, lavender, spiced apple
and odorless solvent as control. The results showed
that all aromas were associated with different al-
pha wave and theta wave distributions. Spiced
apple odor was the most effective in stimulating
alpha activity which seemed to elicit a relaxing
effect of the odor. A study conducted at University
of Occupational and Environmental Health, Kita-
kyushu, Japan (Sugano, 1988; 1989) used changes
of the EEG as indices for the measurement of the
effects of aromas. The aromas of lavender, cineol,
Physiological effects in aromatherapy
Hongratanaworakit, T.
Songklanakarin J. Sci. Technol.
Vol. 26 No. 1 Jan.-Feb. 2004 122
jasmin, sandalwood and alpha-pinene were ex-
plored. A relaxing effect (increase of alpha wave
activity) was found upon presentation of lavender,
cineol, sandalwood and alpha-pinene. In contrast,
a stimulating effect (increase of beta wave activ-
ity) was found upon presentation of jasmin odor.
Nakagawa et al (1992) reported that methyl jus-
monate and cineol aromas inhibited the enhance-
ment of alpha and theta waves which seemed to
show a stimulating effect of the odors. On the other
hand, jasmin lactone odor enhanced the amount of
alpha and theta waves which likely indicated a re-
laxing effect of the odor.
Effect of aromas on contingent negative varia-
tion (CNV)
The contingent negative variation (CNV) is
a slow negative brain potential occurring between
a warning stimulus (S1) and an imperative stimu-
lus (S2). Generally, the CNV is highly sensitive to
psychological variables. Donchin (1973), for in-
stance, found that the instruction set affected CNV
amplitude in identical evocation paradigms. The
CNV is also affected by subject variables such as
anxiety and stress. Knott and Irwin (1967) found a
decrease of the CNV amplitude in anxious subjects.
Studies relating to the use of chlordiazepoxide and
caffeine (known central nervous system depressor
and stimulator, respectively) showed that a decrease
of the CNV was detected after the administration
of chlordiazepoxide and an increase of the CNV
was found after the administration of caffeine
(Janssen et al., 1978). The stimulant increased the
magnitude of the CNV, in contrast, the depressor
decreased the magnitude of the CNV. Investigation
of Ashton and colleagues (1974) also supported
these findings. The CNV was used as an indicator
of the arousal effects of aromas (Torii et al., 1988;
Kanamura et al., 1988). Torii and his group found
that the presentation of jasmin aroma caused a sig-
nificant increase of the CNV, whereas lavender
aroma caused a significant decrease of the CNV.
When subjects took a cup of coffee, the CNV was
changed in the same direction as smelling jasmin,
i.e. an increase of the CNV. It seemed to show a
stimulate effect of jasmin aroma. In contrast, when
subjects took a nap, the CNV was changed in the
same direction as smelling lavender, i.e. a decrease
of the CNV. It likely showed a relaxing/sedative
effect of lavender aroma. Furthermore, Kanamura
et al., (1989) also reported that citrus aromas and
some floral bouquets (described as happy and ex-
cited agents) led to an increase of the CNV. Some
sweet and heavy floral and oriental perfumes led
to a decrease of the CNV. They imply that these
aromas have a direct physiological effect on the
central nervous system arousal thereby altering the
CNV. In a similar work of the Kubota group (1992),
chiral fragrance molecules affected the changes of
the CNV. They reported that l-carvon showed a
sedative effect whereas d-carvone elicited a stimu-
lant effect. Further work by Manley at Takasago
International Corporation (Manley, 1993) was con-
ducted to evaluate various essential oils and aro-
matic chemicals that are used to create fragrances.
The CNV responses to those substances were re-
corded. The results revealed that basil, clove, gera-
nium, lemon grass, nerol, patchouli, peppermint,
rose and ylang ylang caused an increase of the CNV
magnitude (stimulating effect). On the other hand,
bergamot, chamomile, lemon, marjoram and san-
dalwood caused a decrease of the CNV magnitude
(relaxing effect). A few aromas showed mixed or
inconclusive effects on the CNV such as valerian
and sage.
Effect of aromas on eye blink rate or pupil func-
tions
Generally, eye blink rate or pupil dilation/
constriction are indicators of cognitive processing
and the level of arousal (Cramon, 1977). Electro-
oculography is a method of recording eye move-
ment and position by means of potential differences
from electrodes placed around the eyes. Movement
of the eyes is controlled by muscles which are in-
nervated by the CNS.
Steiner et al. (1977) explored the effects of
odors, i.e., rosemary, bromstyrol, tuborose and ba-
nana, on pupil functions. They found all odors elic-
ited pupil enlargement which likely represents an
Physiological effects in aromatherapy
Hongratanaworakit, T.
Songklanakarin J. Sci. Technol.
Vol. 26 No. 1 Jan.-Feb. 2004 123
increase of arousal. In a similar study of Miyazaki
and co-worker (1991), the effects of inhalation of
aromas on the light reflex of the pupil as well as on
performance in a cognitive task were investigated.
They found that orange oil increased the rate of
constriction of the pupil, i.e. increase of the PNS
activity, and decreased the dilatation time of the
pupil, i.e. decrease of the SNS activity. In addition,
sweet fennel oil reduced the mental stress and fa-
tigue caused by a computerized arithmetic assign-
ment. The effect was significant in the measure-
ment of the contraction ratio of the pupil (Nagai et
al., 1991). Recently, Hongratanaworakit et al.,
(2003a) have studied the effects of sandalwood oil
and α-santalol on humans after percutaneous ab-
sorption. They found that both aromas showed a
significantly larger decrease of eye blink rate as
compared to the placebo group. This finding points
towards a decrease of arousal in terms of the ANS.
Concluding remarks
Scientific evaluation of aromatherapy sti-
mulated the issues of the new concepts concerning
the effects of aromas. The changes of physiologi-
cal parameters after receiving the aromas are widely
used for the scientific verification of relaxing/seda-
tive and stimulating effects of aromas. Many com-
mercial aroma products have been developed on
the basis of the new concept of aromatherapy. These
products claimed various effects such as calming/
relaxing, stimulating/uplifting, refreshing, sleep
well, healing and so on. Some products claimed
only one effect, while some claimed more than one
effect. Although the marketability of aroma prod-
ucts has grown considerably, the effects of aromas
have been inconsistent. This trend of research and
development in this field is expected to continue
and to be faithful in assessing the psychological
effects of aromas. Further advanced research on the
endocrine, immunological, pharmacological effects
of aromas has already commenced and should show
significant results in the near future.
Finally, the purpose of this selective review
is to alert aromatherapists to these possible and
current therapeutic applications of aromas. What
is now required is their evaluation through formal
clinical trials. It should be clear from the above dis-
cussion that evaluation will be complex, and will
involve varied skills. It is hoped that this paper en-
courages the necessary collaborations between
aromatherapists, scientists and psychologists in re-
searching this intriguing area.
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... In clinical applications, transnasal inhalation of essential oils can be used nasal inhaler, vapor diffuser, spraying into the air, vapor balms, or direct inhalation by evaporation using tissue or cotton round (Acimovic, 2021). Notably, inhalation of essential oils or aromatic plant volatile oils can send signals directly to the olfactory system and trigger the brain to produce neurotransmitters e.g., serotonin and dopamine], influence the neuroendocrinological system, neurophysiological brain activity, sympathetic and parasympathetic nervous system, biomarkers changes, psychological and behaviour effects, and to modulate mental disorders further (Masago et al., 2000;Hongratanaworakit, 2004;Lahlou, 2004;Watanuki and Kim, 2005;Strous and Shoenfeld, 2006;Tanida et al., 2008;MPham et al., 2012;Lv et al., 2013;Angelucci et al., 2014). From this, it can be seen that inhalation aromatherapy on mental disorders is due to the pharmacological effect caused by systemic absorption or act on the nervous system, but not only due to the psychological perception of the scent (Scuteri et al., 2019). ...
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... [20] It has shown an increase in blood flow and decrease in galvanic skin conductance and systolic blood pressure. [21] Two basic mechanisms are offered to explain the effects. ...
... It produces a feeling of exuberance, confidence, and offers chilling and relaxing effects. It is a natural and pure aphrodisiac (Hongratanaworakit, 2004(Hongratanaworakit, , 2010Tanida, 2008;Hongratanaworakit, 2010;Purohit et al., 2016). Tamil Nadu was one among the leading producers of Jasmine in the country with an annual output of 77, 267 tons from a cultured area of 9360 hectares and was in a second position in India in the area under flower cultivation (0.27 lakh ha) as well as production of loose flowers (3.13 lakh tons) in the year 2012-13 (Guledagudda, 1996;Jyothi, and Raju, 2003;Ambika, 2012;Sarka, 2016). ...
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