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Pharmaceutical and Therapeutic Potentials of Essential Oils and Their Individual Volatile Constituents: A Review

Article · Literature Review (PDF Available) inPhytotherapy Research 21(4):308-23 · April 2007with2,571 Reads
DOI: 10.1002/ptr.2072} · Source: PubMed
Essential oils and their volatile constituents are used widely to prevent and treat human disease. The possible role and mode of action of these natural products is discussed with regard to the prevention and treatment of cancer, cardiovascular diseases including atherosclerosis and thrombosis, as well as their bioactivity as antibacterial, antiviral, antioxidants and antidiabetic agents. Their application as natural skin penetration enhancers for transdermal drug delivery and the therapeutic properties of essential oils in aroma and massage therapy will also be outlined.
Copyright © 2007 John Wiley & Sons, Ltd. Phytother. Res. (in press)
DOI: 10.1002/ptr
Copyright © 2007 John Wiley & Sons, Ltd.
Phytother. Res. (in press)
Published online in Wiley InterScience
( DOI: 10.1002/ptr.2072
Pharmaceutical and Therapeutic Potentials of
Essential Oils and Their Individual Volatile
Constituents: A Review
Amr E. Edris*
Aroma and Flavor Chemistry Department, National Research Center, Dokki, El Behose Street, Dokki, 12622, Cairo, Egypt
Essential oils and their volatile constituents are used widely to prevent and treat human disease. The possible
role and mode of action of these natural products is discussed with regard to the prevention and treatment of
cancer, cardiovascular diseases including atherosclerosis and thrombosis, as well as their bioactivity as antibac-
terial, antiviral, antioxidants and antidiabetic agents. Their application as natural skin penetration enhancers
for transdermal drug delivery and the therapeutic properties of essential oils in aroma and massage therapy
will also be outlined. Copyright © 2007 John Wiley & Sons, Ltd.
Keywords: essential oils; cancer; cardiovascular disease; antimicrobial; antidiabetic; penetration enhancer; aromatherapy; massage
Received 6 December 2005
Revised 31 October 2006
Accepted 31 October 2006
* Correspondence to: Amr E. Edris, Aroma and Flavor Chemistry De-
partment, National Research Center, Dokki, El Behose Street, Dokki,
12622, Cairo, Egypt.
Aromatic plants had been used since ancient times
for their preservative and medicinal properties, and
to impart aroma and flavor to food. Hippocrates,
sometimes referred to as the ‘father of medicine’, pre-
scribed perfume fumigations.
The pharmaceutical properties of aromatic plants are
partially attributed to essential oils. The term ‘essential
oil’ was used for the first time in the 16th century
by Paracelsus von Hohenheim, who named the effec-
tive component of a drug, ‘Quinta essential’ (Guenther,
1950). By the middle of the 20th century, the role
of essential oils had been reduced almost entirely to
use in perfumes, cosmetics and food flavorings, while
their use in pharmaceutical preparations had declined.
Essential oils are natural, complex, multi-component
systems composed mainly of terpenes in addition to
some other non-terpene components. Several techniques
can be used to extract essential oils from different parts
of the aromatic plant, including water or steam distilla-
tion, solvent extraction, expression under pressure,
supercritical fluid and subcritical water extractions.
Most cancer chemotherapy regimens make use of highly
cytotoxic drugs that target proliferating cell populations.
The non-discriminatory nature of these drugs leads to
severe side effects in normal cells with a high prolifera-
tive index, such as those of the gastrointestinal tract
and bone marrow, thus limiting the effective dose of
anticancer drug that can be administered. The diverse
therapeutic potential of essential oils has drawn the
attention of researchers to test them for anticancer
activity, taking advantage of the fact that their mecha-
nism of action is dissimilar to that of the classic cytotoxic
chemotherapeutic agents (Rajesh et al., 2003). Early
reports had indicated that essential oil components,
especially monoterpenes, have multiple pharmacolo-
gical effects on mevalonate metabolism which could
account for the terpene-tumor suppressive activity
(Elson, 1995).
Monoterpenes have been shown to exert chemopre-
ventive as well as chemotherapeutic activities in
mammary tumor models and thus may represent a new
class of therapeutic agents. The mechanism of action
of monoterpenes is based on two main approaches,
chemoprevention and chemotherapy. Chemoprevention
occurs during the initiation phase of carcinogenesis
to prevent the interaction of chemical carcinogens with
DNA, by induction of phase I and phase II enzymes
to detoxify the carcinogen (Wattenberg, 1992). Chemo-
therapy works during the promotion phase, in which
inhibition of tumor cell proliferation, acceleration of
the rate of tumor cell death and/or induction of tumor
cell differentiation may occur (Morse and Stoner, 1993).
It is generally accepted that components that induce
Phase I or II drug metabolizing enzymes can protect
against chemical carcinogenesis or damage, especially
during the initiation phase. Essential oils could be
utilized to protect body organs against carcinogenesis;
for instance, nutmeg, (Myristica fragrans), showed a
potent hepatoprotective activity against liver damage
Copyright © 2007 John Wiley & Sons, Ltd. Phytother. Res. (in press)
DOI: 10.1002/ptr
caused by certain chemicals (Morita et al., 2003). The
protective activity was correlated with myristicin, a
major constituent. The mechanism of hepatoprotective
activity of myristicin includes inhibition of TNF-
release from macrophages and suppression of apoptosis.
Myristicin can also induce glutathione-S-transferase,
a phase II detoxifying enzyme (Ahmad et al., 1997),
in addition to its activity of inhibiting benzo[a]pyrene-
induced tumorigenesis in mouse tissues (Zheng et al.,
1992). Recently it was found that myristicin induces
cytotoxicity in human neuroblastoma SK-N-SH cells by
an apoptotic mechanism (Lee et al., 2005).
Citral, which is found in many essential oils and
comprises 70%–85% of lemongrass oil, is a novel
monoterpene inducer of glutathione-S-transferase class
, (GSTP1). This isozyme is responsible for the increase
in the total GST activity of the citral-treated rat
hepatocyte cells (Nakamura et al., 2003). Structure–
activity relationship studies revealed that trans-citral
(geranial) was the main contributor for the induction
of GSTP1. The aldehyde group conjugated with a trans-
double bond in trans-citral is an essential structural
factor for GST induction. On the other hand cis-citral
(neral) showed no activity. This suggested the explora-
tion of citral as a cancer chemopreventive agent
targeted towards inflammation-related carcinogenesis
such as skin cancer (Henderson et al., 1998) and colon
cancer (Mulder et al., 1995), both of which were found
to be due to lack of GSTP1 activity. The high content
of citral in lemongrass oil may explain the inhibitory
effect of that aromatic plant on the early phase of
hepatocarcinogenesis in rats (Puatanachokchai et al.,
2002). Citral also increased the hepatic glutathione-
S-transferase (GST) and aminopyrine demethylase
activities, and reduced glucuronyl transferase activity
(Vinitketkumnuen and Lertprasertsuk, 1997).
Although citral is generally recognized as safe for
human consumption as a food additive by the FDA
(GRAS), it is classified as a potential teratogen and
primary irritant (Abramovici and Rachmuth-Roizman,
1983). The National Toxicology Program (2003) con-
cluded that under the conditions of two-year feeding
studies there was no evidence of carcinogenic activity
of citral in male or female F344/N rats exposed to 1000,
2000 or 4000 ppm. There was no evidence of carcino-
genic activity of citral in male B6C3F1 mice exposed to
500, 1000 or 2000 ppm. There was, however, equivocal
evidence of carcinogenic activity in female B6C3F1
mice based on the increased incidence of malignant
lymphoma, thus the acceptable daily intake (ADI) of
citral has been proposed as 0–0.5 mg/kg/day (FAO/
WHO 2003).
Other essential oils elicit hepatoprotective activity
due to their phenolic and/or monoterpene content:
for example, black cumin (Nigella sativa), due to
thymoquinone (Mansour et al., 2001); orange essential
oil, due to d-limonene (Bodake et al., 2002); and sweet
fennel (Foeniculum vulgare) due to both d-limonene
-myrcene (Ozbek et al., 2003). In addition,
d-limonene exhibits chemopreventive efficacy in
preclinical hepatocellular carcinoma models (Parija and
Das, 2003; Guyton and Kensler, 2002; Jiri et al., 1999).
The mode of action originates, in part, from the induc-
tion of the specific cytochrome P450 isozymes includ-
ing CYP 2B1 and CYP2C (Maltzman et al., 1991).
d-Limonene is also a candidate for the chemoprevention
of skin cancer (Stratton et al., 2000), although it can
cause contact dermatitis, especially when oxidized.
Garlic essential oil is a rich source of volatile organo-
sulfur components (OSCs). These compounds are recog-
nized as a group of potential cancer chemopreventive
agents due to their activity for modulating phase I and
II drug detoxifying enzymes (Milner, 2001). The three
major OSCs of garlic essential oil, diallyl sulfide (DAS),
diallyl disulfide (DADS) and diallyl trisulfide (DATS),
were found differentially to mediate the transcriptional
levels of phase II detoxifying enzymes, NQO1 and HO1,
in human hepatoma (HepG2) cells (Chen et al., 2004).
DATS, with three sulfur atoms, was found to be the
most potent inducer of phase II enzyme gene expres-
sion, ARE activation and Nrf2 protein accumulation.
The effects of oral administration of garlic essential oil
and its three major OSCs on different phase I and phase
II hepatic detoxification enzymes in rat showed that
the essential oil and DAS significantly increased the
activity of the phase I enzyme (PROD) (Wu et al., 2002).
DADS and DATS significantly decreased the activity
of phase I enzyme (NDMAD). Garlic essential oil,
DADS, and DATS significantly increased the activity
of glutathione S-transferase, a phase II detoxifying
enzyme. The placental form of GST (GST
) level
was also increased by garlic oil and its three major
components. GST
is one of the GST isozymes which
are of special interest due to their relationship with
the development of human ovarian cancer (Hamada
et al., 1994) and colorectal cancer (Mulder et al., 1995).
The highest concentrations of DAS, DADS and DATS,
which are decomposition products of allicin, are found
in garlic essential oil extracted from crushed cloves using
steam or water distillation (Ibrel et al., 1990).
Cancer suppression
Essential oils and their individual aroma components
showed cancer suppressive activity when tested on a
number of human cancer cell lines including glioma,
colon cancer, gastric cancer, human liver tumor,
pulmonary tumors, breast cancer, leukemia and others.
Glioma is one of the most malignant human tumors
(De Angelis, 2001).
–Bisabolol, a major sesquiterpene alcohol in Chamo-
mile, (Matricaria chamomilla) essential oil, could be
considered as a promising inducer of apoptosis in highly
malignant glioma cells. It is neither toxic in animals nor
does it reduce the viability of normal astroglial cells
(Cavalieri et al., 2004). A significant effect on the treat-
ment of glioma was reported using the sesquiterpene
hydrocarbon elemene which is found in small amounts
in many essential oils: it prolonged quality survival time
of patients with glioma (Tan et al., 2000).
Geraniol, a monoterpene alcohol, elicited a dramatic
reduction in the amounts of thymidylate synthase (TS)
and thymidine kinase (TK) expression in colon cancer
cells (Carnesecchia et al., 2004). These two enzymes
are involved in 5-fluorouracil (5-FU) toxicity, in that a
decrease in these enzymes is related to enhanced 5-FU
cytotoxicity (Mans et al., 1999). Geraniol lowered the
resistance of cancer cells to 5-FU thus potentiating the
inhibition of tumor growth by the drug, and increasing
the survival time of nude mice grafted with the human
colorectal tumor cells TC118. Geraniol acts on at least
Copyright © 2007 John Wiley & Sons, Ltd. Phytother. Res. (in press)
DOI: 10.1002/ptr
two different targets involved in the resistance of
cancer cells to 5-FU: it increases cell membrane
permeability leading to enhanced uptake of 5-FU by
colon cancer cells and causes a significant change in
the resting potential and cell membrane polarization,
which may trigger modifications of membrane bound
protein activity and alterations in intracellular signal-
ing pathways (Carnesecchi et al., 2002a, 2002b). A
major natural source of geraniol is Palmarosa oil
(Cymbopogon martini var martini), also known as East
Indian geranium, containing 59%–84% which is much
greater than most species of Geranium or Pelargonium
(Sirinivas, 1986).
d-Limonene showed antiangiogenic and proapoptotic
effects on human gastric cancer implanted in nude mice,
thus inhibiting tumor growth and metastasis (Guang
et al., 2004). d-Limonene can also induce the formation
of apoptotic bodies on BGC-823 gastric cancer cells in
a dose- and time-dependent manner (Guang et al., 2003)
and its efficacy was increased by combining it with
cytotoxic agents such as 5-fluorouracil. Administra-
tion of chow pellets containing 1% or 2% d-limonene
to male Sprague-Dawley rats resulted in significant
reductions in chemically induced, hepatocellular
carcinomas (Kaji et al., 2001). This effect could be re-
lated to its effect in inhibiting cell proliferation and
in enhancing apoptosis. d-Limonene also increased the
survival of lymphoma-bearing mice and modulated
the immune response, showing significant potential for
clinical application (Del Toro-Arreola et al., 2005). A
mechanism that may contribute to d-limonene efficacy
in the chemoprevention and/or therapy of chemically
induced human solid tumor cells has been proposed
(Chen et al., 1999; Jiri et al., 1999; Parija and Das, 2003).
Briefly, d-limonene can, in part, inhibit FPTase activ-
ity, inhibit the plasma-membrane associated P21ras
expression, and the post-translational isoprenylation
of P21ras. d-Limonene is found naturally in many
essential oils, especially citrus fruit peel where it con-
stitutes 90%–95% of the total oil. It is also found in
considerable amounts (26%–34%) in some spearmint
essential oils (Edris et al., 2003). The annual produc-
tion of d-limonene was estimated to be 50 000 tonnes
(Braddock and Cadwallader, 1995) which makes its price
as low as $1–2/kg (Mazzaro, 2000).
Diallyl trisulfide (DATS), a major constituent of
garlic essential oil, showed a high activity for arresting
the division of human liver tumor cells (J5) at the G2/
M phase of the cell cycle (Wu et al., 2004). The mecha-
nism of action probably involves regulating the protein
expressions of cyclin B1 and Cdk7. The chemother-
apeutic and chemopreventive activity of garlic essential
oil and its various organo-sulfur constituents against
different types of carcinogenesis have been reviewed
elsewhere (Thomson and Ali, 2003; Benjamin et al.,
It is accepted that aberrant angiogenesis is essential
for the progression of solid tumors and hematological
malignancies. Thus, antiangiogenic therapy is one of
the most promising approaches to control cancer.
Perillyl alcohol (POH) which is the hydroxylated ana-
logue of d-limonene, has the ability to interfere with
angiogenesis (Loutrari et al., 2004). POH either alone
or with PA (perillic acid, the major metabolite of POH
in the body), has a potential use as an anticancer drug
that stimulates different types of tumors to apoptosis,
inhibits their proliferation, or overcomes their resist-
ance to chemo-/radiotherapy (Yuri et al., 2004; Samaila
et al., 2004; Elegbede et al., 2003; Clark et al., 2003;
Rajesh et al., 2003; Rajesh and Howard 2003; Ahn
et al., 2003; Bardon et al., 2002; Burke et al., 2002;
Bardon et al., 1998). The antitumor activity of POH
emanates from its activity of modulating cellular pro-
cesses that control cell growth and differentiation (Azzoli
et al., 2003; Clark et al., 2002; Ariazi et al., 1999; Ren
and Gould, 1998; Gould, 1997 and Gould, 1995). Thus
POH, among other micronutrients, was investigated by
the National Cancer Institute (NCI) in NCI-sponsored
phase I, II, or III chemoprevention trials for prostate,
breast and colon cancers (Greenwald et al., 2002). How-
ever, it may not be an effective chemopreventive agent
for esophageal cancer in humans (Liston et al., 2003).
Unfortunately, despite evidence of anticancer activity
of POH in vitro, oral administration has not yet shown
any clinical antitumor activity (Bailey et al., 2004; Azzoli
et al., 2003; Liu et al., 2003; Meadows et al., 2002; Howard
et al., 2002). POH is found in small amounts in many
aromatic plants including lavender, peppermint, spear-
mint, perilla and lemongrass (Kelloff et al., 1996). Conyza
newii oil, (Compositae), contains 4.2% of perillyl alcohol
(Omolo et al., 2004) while Tetradenia riparia oil,
(Labiateae) contains 6.0% POH (Campbell et al., 1997).
POH can also be produced from d-limonene by micro-
bial biotransformation pathways (Duetz et al., 2003).
Eucalyptol (1,8-cineol) is found in high concentrations
(60%–90%) in the essential oil of eucalyptus (Eucalyp-
tus globulus) (Juergens et al., 1998) and 59% in car-
damom (Elettaria cardamomum, Zingbraceae) (Huang
et al., 1999). Treatment of human leukemia HL-60
cells with eucalyptol showed morphological changes,
(fragmentations of DNA) indicating an induction
of apoptosis (Moteki et al., 2002). However, this
effect was not shown in human stomach cancer KATO
III cells that received the same treatment with
In addition to the individual terpene components
mentioned above, several whole essential oils have
also shown anticancer activity in vitro. The essential
oil of lemon balm (Melissa officinalis L) was found
to be effective against a series of human cancer cell
lines (A549, MCF-7, Caco-2, HL-60, K562) and a
mouse cell line (B16F10) (De Sousa et al., 2004)
and that of Artemisia annua L. induced apoptosis
of cultured SMMC-7721 hepatocarcinoma cells (Li
et al., 2004). The essential oil of Australian tea tree
(Melaleuca alternifolia) and its major monoterpene
alcohol, terpinen-4-ol, were able to induce caspase-
dependent apoptosis in human melanoma M14 WT
cells and their drug-resistant counterparts, M14
adriamicin-resistant (Calcabrini et al., 2004). There
was evidence to suggest that the effect of the total oil
and of terpinen-4-ol was mediated by their interac-
tion with the plasma membrane and subsequent
reorganization of membrane lipids.
Hepatic arterial infusion with Curcuma oil had a
similar positive effect in treating primary liver cancer
as that of the chemical drugs (Cheng et al., 2001). The
essential oil of Tetraclinis articulate, (a conifer tree)
showed the hallmarks of apoptosis when tested on a
number of human cancer cell lines including melanoma,
breast and ovarian cancer in addition to peripheral
blood lymphocytes (Buhagiar et al., 1999).
Copyright © 2007 John Wiley & Sons, Ltd. Phytother. Res. (in press)
DOI: 10.1002/ptr
These results may draw the attention of cancer
researchers to further extend their clinical testing of
essential oils, and it would be interesting to investigate
the antitumor activity of a major individual terpene
constituent in comparison with its whole essential oil
Atherosclerosis is a process in which deposits of plaque
build up in the innermost layer of the artery, the intima
(Barter, 2005). Plaque can eventually significantly re-
duce blood flow, leading to serious health problems.
Increased concentrations of oxidatively modified low
density lipoproteins (LDLs) in cholesterol play a
substantial role in disease initiation (Barter, 2005;
Valenzuela et al., 2004; Steinberg, 1997, Daugherty and
Roselaar, 1995). Atherosclerosis can therefore be slowed
down or inhibited by preventing the oxidation of LDLs
using a high daily intake of antioxidants.
Essential oils and their aroma volatile constituents
have shown an antioxidative activity against LDL
oxidation. Terpinolene, a monoterpene hydrocarbon,
can effectively inhibit the oxidation of both the lipid
part and the protein part of LDL. This inhibition is due
to a retarded oxidation of intrinsic carotenoids of LDL,
and not, as is the case with some flavonoids, to the
protection of intrinsic
-tocopherol (Grassmann et al.,
2003, 2005). Essential oils rich in phenolic constituents
such as eugenol and thymol have the highest anti-
oxidative activity against LDL oxidation (Naderi et al.,
2004) and these components can also change the
affinity of the LDL particles for the LDL receptor. A
relationship was found between the quantity and qual-
ity of phenolic components in the oil and its protection
against LDL oxidation: for instance, copper-catalysed
oxidation of human LDL in vitro is inhibited by 50%–
100% when eugenol is the major component of the
essential oil (as in clove oil), while inhibition was only
10%–50% for essential oils containing moderate
amounts of the phenolics, thymol, carvacrol or cuminol
(Teissedre and Waterhouse, 2000). In addition to the
phenolic constituents, the monoterpene hydrocarbon
terpinene, was also found to inhibit LDL oxidation,
even in the propagation phase.
-Terpinene generated
an antioxidative effect on the Cu2+-induced and AAPH-
induced oxidation of human LDL in vitro (Takahashi
et al., 2003). Tea tree essential oil is considered to be a
rich source of
-terpinene (23.0%) (Brophy et al., 1989)
-terpinene is also found in considerable amounts
in some citrus peel essential oils such as bergamot
(14%), mandarin (17%) and lemon (10%) (Mondello
et al., 1995). It has been recommended as an addition
to foods and beverages to protect against LDL oxida-
tion and to reduce plaque formation (Takahashi et al.,
Essential oils and some of their individual constitu-
ents can also lower total plasma cholesterol and
triglyceride levels which contribute to the formation of
plaque and consequently, atherosclerosis. Black cumin
oil (Nigella sativa Linn.) was found to decrease plasma
concentrations of cholesterol and triglycerides due to
the high content of thymoquinone (Ali and Blunden,
2003). The essential oil of Satureja khuzestanica,
an endemic plant of Iran, was reported to decrease
the normal blood lipid peroxidation level (Abdollahi
et al., 2003). Oral administration of dill seed essential
oil (Anethum graveolens) reduced triacylglyceride
levels by almost 42%, although total cholesterol
level was not reduced (Yazdanparast and Alavi, 2001).
-Curcumene, the major constituent (approx. 65%)
of the essential oil of Javanese turmeric (Curcuma
xanthorrhiza), exerts triglyceride-lowering activity on
serum as well as liver triglycerides (Yasni et al.,
Garlic essential oil significantly lowered serum
cholesterol and triglycerides while raising the level of
high-density lipoproteins in both healthy individuals
and patients with coronary heart disease (Bordia, 1981).
The hypolipidemic action of garlic oil is primarily due
to a decrease in hepatic cholesterogenesis (Mathew
et al., 1996). One of the consequences of atherosclerosis
is hypertension, and some essential oils exert hypoten-
sive activity when applied in vivo. Oral administration
of combinations of oregano, cinnamon, cumin, and other
essential oils decreased systolic blood pressure in rats
(Talpur et al., 2005) and intravenous administration of
the essential oil from the aerial parts of Mentha x villosa
induced a significant and dose-dependent hypotension
associated with decreases in heart rate (Guedes et al.,
2004). This activity was attributed to the volatile com-
ponent, piperitenone oxide, which represents 55.4% of
the oil. The hypotensive effect induced by the oil is
probably due to its direct cardiodepressant action and
peripheral vasodilation, which can be attributed to both
endothelium-dependent and endothelium-independent
Intravenous administration of the essential oil of
basil (Ocimum gratissimum) induced an immediate
and significant hypotension and bradycardia (Lahlou
et al., 2004). The hypotensive activity of the essential
oil resulted from its vasodilator effects, acting directly
upon vascular smooth muscle. This effect was attrib-
uted, at least in part, to the actions of eugenol, which is
the major constituent of the oil. Clove bud essential oil
is the richest source of eugenol known (about 80%;
Deyama and Horiguchi, 1971) but from a safety point
of view, care must be taken in dealing with eugenol
due to its suspected carcinogenicity and hepatotoxicity
(National Toxicology Program, 1983).
Intravenous injection of the monoterpene alcohol
terpinen-4-ol decreased mean aortic blood pressure in
a dose-related manner, in conscious DOCA-salt hyper-
tensive rats (Lahlou et al., 2003). The mechanism of
action was related to the induction of vascular smooth
muscle relaxation rather than enhanced sympathetic
nervous system activity. Terpinene-4-ol is a major
constituent of several essential oils, particularly tea tree
(Brophy et al., 1989) and sweet marjoram essential oils
(Nykanen, 1986).
Essential oils and thrombosis
Thrombosis is usually associated with platelet activa-
tion and the release of eicosanoids which contribute to
initiation and aggravation of thrombosis. Prevention of
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DOI: 10.1002/ptr
thrombogenesis has become one of the most important
targets for the prophylaxis and therapy of cardiocir-
culatory disorders with thromboembolic complications
(Fitzgerald, 2001). The antiplatelet agents currently
used for this purpose are effective in the prevention of
thromboembolic disease, but many have side effects
such as gastric erosion (e.g. aspirin), agranulocytosis
(e.g. ticlopidine), or show a poor separation between
therapeutic efficacy and hemorrhagic complications
(Van De Graaff and Steinhubl, 2001). For this reason,
plant extracts have been tested for their potential
antithrombotic activity. The essential oil of lavender,
(Lavandula hybrida Reverchon cv.), showed a broad
spectrum antiplatelet effect and was able to inhibit plate-
let aggregation induced by ADP, arachidonic acid,
collagen and the stable thromboxane receptor agonist
U46619 with no prohemorrhagic properties (Ballabenia
et al., 2004). Linalyl acetate (36% of lavender oil)
seemed to be the main active antiplatelet agent. Onion
(Allium cepa) is well known for promoting cardiovas-
cular health, and populations with a high consump-
tion of onions are associated with decreased rates of
atherosclerosis or thrombotic disease (Kendler, 1987).
This activity is due to inhibition of platelet aggrega-
tion and thromboxane formation by the organo-sulfur
components in the essential oil (Bordia et al., 1996;
Srivastava, 1986). The mechanism of the antiplatelet
effect of onion includes TXA2 synthase inhibition and
TXA2/PGH2 receptor blockade (Moon et al., 2000).
However, garlic was found to be more potent than onion
in lowering TXB2 levels (Bordia et al., 1996). Organo-
sulfur components such as allicin, isolated from garlic
essential oil, showed a potent inhibition of platelet
aggregation (Calvey et al., 1994; Lawson et al., 1992).
Allicin is formed from alliin when garlic cloves are
crushed or chewed and the enzyme alliinase is released
from the cell walls. However, ajoene has the highest
specific antithrombotic activity compared with any other
organo-sulfur compounds from garlic (Lawson et al.,
1992; Apitz-Castro et al., 1983). Ajoene is formed from
allicin during steam or water distillation of the essen-
tial oil from garlic cloves, or during storage in ethanol
(Block et al., 1986, Iberl et al., 1990). The presence
of vinyl groups attached by a disulfide bond makes
ajoene a highly reactive molecule which can inhibit
the release of both dense granules and
(Rendu et al., 1989). Ajoene can reduce platelet aggre-
gation induced by 0.1 U/mL thrombin by 94.7% after
a pre-stimulation incubation time for one minute at a
dose of 25 µM (Villar et al., 1997). The mechanism of
action of ajoene differs to that of other known inhibi-
tors of platelet aggregation. Ajoene penetrates the
membrane of intact platelets and reduces the viscosity
of the inner part of the lipid bilayer (Rendu et al., 1989),
thus interfering with the expression of the fibrinogen
3 at the cell surface, thereby inhibiting
fibrinogen binding (Apitz-Castro et al., 1986). Ajoene
also inhibits platelet aggregation through inhibiting the
formation of thromboxane A2 via altering arachidonic
acid metabolism. Moreover, it inhibits platelet aggre-
gation induced by adrenaline, collagen, adenosine
diphosphate and calcium ionophore A23187 (Srivastava
and Tyagi, 1993). Polysulfides, particularly dimethyl
trisulfide and diallyl trisulfide, found in both onion and
garlic oils also inhibit thromboxane synthesis in plate-
lets (Makheja and Bailey, 1990).
The Ancient Egyptians used aromatic plants in
embalming to stop bacterial growth and prevent decay,
an effect attributed to a great extent to their essential
oils. Strong in vitro evidence indicates that essential
oils can act as antibacterial agents against a wide spec-
trum of pathogenic bacterial strains including Listeria
monocytogenes, L. innocua, Salmonella typhimurium,
Escherichia coli O157:H7, Shigella dysenteria, Bacillus
cereus, Staphylococcus aureus and Salmonella typhi-
murium (Schmidt et al., 2005; Jirovetz et al. 2005; Burt,
2004; Dadalioglu and Evrendilek, 2004; Nguefack
et al., 2004; Hulin et al., 1998) and many more (Deans
and Ritchie, 1987). Thyme and oregano essential oils
can inhibit some pathogenic bacterial strains such as
E. coli, Salmonella enteritidis, Salmonella choleraesuis
and Salmonella typhimurium (Penalver et al., 2005), with
the inhibition directly correlated to the phenolic com-
ponents carvacrol and thymol. The same correlation
was also confirmed for oils rich in carvacrol alone
(Santoyo et al., 2006). Eugenol and carvacrol showed
an inhibitory effect against the growth of four strains of
Escherichia coli O157:H7 and Listeria monocytogenes
(Gaysinsky et al., 2005). The presence of a phenolic
hydroxyl group, in carvacrol particularly, is credited with
its activity against pathogens such as Bacillus cereus
(Ultee et al., 1999; Ultee et al., 2002). Some essential
oils demonstrated antibacterial activity against zoonotic
enteropathogens including Salmonella spp., Escherichia
coli O157, Campylobacter jejunii and Clostridium
perfringens. Thus, these oils could possibly be used as
an alternative to antibiotics in animal feed (Wannissorn
et al., 2005).
Essential oils with high concentrations of thymol and
carvacrol e.g. oregano, savory and thyme, usually in-
hibit Gram-positive more than Gram-negative patho-
genic bacteria (Nevas et al., 2004). However the essential
oil of Achillea clavennae exhibited strong antibacterial
activity against the Gram ()-ve Haemophilus influenzae
and Pseudomonas aeruginosa respiratory pathogens,
while Gram (+)-ve Streptococcus pyogenes was the most
resistant to the oil (Skocibusic et al., 2004).
The major mode of infection transmission in hospital-
acquired infections is thought to be through hand
carrying of pathogens from staff to patient, and from
patient to patient (Boyce and Pittet, 2002; Naikoba
and Hayward, 2001), and a relationship between hand
hygiene and reduced transmission of infections been
reported (Reybrouck, 1986). Most antiseptic agents can
damage the skin, leading to a change in microbial flora,
and an increased shedding of the original protective
bacterial flora of the hand leads to an increased risk of
transmission of pathogenic microorganisms (Larson,
2001). Reports suggest that repeated use of formula-
tions containing tea tree essential oil (TTO) does not
lead to dermatological problems, nor affect the original
protective bacterial flora of the skin (Carson and Riley,
1995), so the antibacterial activity of some skin-wash
formulas containing TTO as well as pure TTO was
evaluated against Staphylococcus aureus, Acinetobacter
baumannii, Escherichia coli and Pseudomonas
aeruginosa (Messager et al., 2005a, 2005b). All formu-
lations showed antibacterial activity, but the efficacy of
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DOI: 10.1002/ptr
TTO appeared to be dependent on the formulation and
the concentration tested. The antibacterial activity of
tea tree essential oil has recently been reviewed (Carson
et al., 2006).
In the field of veterinary therapy, a cream formula-
tion containing 10% TTO caused significant and fast
relief against canine localized acute and chronic
dermatitis compared with commercial skin care
cream (Reichling et al., 2004). For the safe use of
tea tree essential oil as antibacterial agent for animals
or humans, the potential toxicity should be taken into
consideration (Carson et al., 2006; Hammer et al., 2005;
Carson and Riley, 1995).
The emergence of resistant pathogenic micro-
organisms in hospitals and in the community repre-
sents a problem for both the treatment of patients and
control of infection. Topical preparations containing
TTO can be considered in regimens for eradication
of methicillin-resistant Staphylococcus aureus in hos-
pitals (Dryden et al., 2004). The preparations were
found to be effective, safe and well tolerated. TTO
demonstrated a relatively short killing time (less than
60 min) for multidrug-resistant organisms, including
methicillin-resistant Staphylococcus aureus (MRSA),
glycopeptide-resistant Enterococci, aminoglycoside-
resistant Klebsiellae, Pseudomonas aeruginosa and
Stenotrophomonas maltophilia (May et al., 2000). MRSA
showed the highest resistance and longest time for eradi-
cation. It was concluded that the antimicrobial activity
of TTO is attributed to its high content of terpenen-4-ol.
Other multidrug-resistant pathogens such as
Pseudomonas aeruginosa and Escherichia coli can be
effectively inhibited by the essential oil of oregano
(Bozin et al., 2006).
Ocimum gratissimum essential oil can also inhibit
extracellular protease and the expression of O-lipopoly-
saccharide rhamnose in virulence and multidrug-resist-
ant strains of 22 Shigellae (Iwalokun et al., 2003). Thus,
the oil may find a use as a therapeutic measure against
shigellosis. Methicillin-resistant Staphylococcus aureus
can also be inhibited by the application of peppermint
and spearmint essential oils (Imai et al., 2001).Essen-
tial oils could be used as antibacterial agents against
some respiratory tract pathogens. The oil of Achillea
clavennae showed its maximum activity against Klebsiella
pneumoniae and penicillin-susceptible and penicillin-
resistant Streptococcus pneumoniae. The oil also exhib-
ited strong activity against Haemophilus influenzae and
Pseudomonas aeruginosa (Skocibusic et al., 2004).
An increased density of Helicobacter pylori in the
gastric mucosa is associated with severe gastritis and an
increased incidence of peptic ulcers (Kelly, 1998). The
activities of 60 essential oils against H. pylori P1 were
evaluated: 30 oils were able to affect the growth
in vitro, and 15 showed strong activity (Bergonzelli
et al., 2003). Among the individual constituents of these
oils, carvacrol, isoeugenol, nerol, citral and sabinene
exhibited the strongest anti-H. pylori effects. Further
investigations are underway regarding the ability of
essential oils to control H. pylori infections (McNulty
et al., 2001; Kalpoutzakis et al., 2001; Imai et al., 2001;
O’Gara et al., 2000).
Essential oils show bactericidal activity against
oral and dental pathogenic microorganisms and can
be incorporated into rinses or mouth washes for
pre-procedural infection control (Yengopal, 2004a),
general improvement of oral health (Yengopal, 2004b),
interdental hygiene (Yengopal, 2004c) and to control
oral malodor (Yengopal, 2004d). Croton cajucara Benth
essential oil was found to be toxic for some pathogenic
bacteria and fungi associated with oral cavity disease
(Alviano et al., 2005) and may be useful for controlling
the microbial population in patients with fixed ortho-
dontic appliances. A 6-month controlled clinical study
demonstrated that a mouthrinse containing essential oils
showed a comparable antiplaque and antigingivitis
activity to that containing the synthetic antibacterial
agent, chlorhexidine (Charles et al., 2004). Mouth rinses
containing essential oils (specially phenolic rich types)
with chlorhexidine gluconate are commonly used as
preprocedural preparations to prevent possible dis-
ease transmission, decrease chances of postoperative
infection, decrease oral bacterial load and decrease
aerosolization of bacteria (Hennessy and Joyce, 2004).
Mouth washes containing essential oils could also
be used as a part of plaque-control routine since they
can penetrate the plaque biofilm, kill pathogenic-
plaque-forming microorganisms by disrupting their cell
walls and inhibiting their enzymatic activity (Ouhayoun,
2003). In addition, essential oils in mouth washes pre-
vent bacterial aggregation, slow the multiplication and
extract bacterial endotoxins (Seymour, 2003).
The mechanisms by which essential oils can inhibit
microorganisms involve different modes of action, and
in part may be due to their hydrophobicity. As a result,
they get partitioned into the lipid bilayer of the cell
membrane, rendering it more permeable, leading to
leakage of vital cell contents (Burt, 2004; Juven et al.,
1994; Kim et al., 1995). Impairment of bacterial enzyme
systems may also be a potential mechanism of action
(Wendakoon and Sakaguchi, 1995).
Herpes simplex virus (type I, II) causes some of the
most common viral infections in humans, and can be
fatal. Synthetic antiviral drugs have been used to treat
Herpes infections (Fahad and Stepher, 1996; Wagstaff
et al., 1994), but not all are efficacious in treating
genital herpes infections. HSV-1 and HSV-2 have also
developed resistance to one of these (acyclovir) mainly
in immuno-compromised hosts (Birch et al., 1990;
Wagstaff et al., 1994). Plant extracts, especially essen-
tial oils, may afford a potential alternative to synthetic
antiviral drugs: they have demonstrated virucidal prop-
erties, with the advantage of low toxicity compared with
the synthetic antiviral drugs (Baqui et al., 2001; Primo
et al., 2001; Schnitzer et al., 2001). Incorporation of
Artemisia arborescens essential oil in multilamellar
liposomes greatly improved its activity against intra-
cellular Herpes simplex virus type-1 (HSV-1) (Sinicoa
et al., 2005). Melissa officinalis L. essential oil can
inhibit the replication of HSV-2, due to the presence
of citral and citronellal (Allahverdiyev et al., 2004)
and the ability to replicate of HSV-1 can be suppressed
by incubation with different essential oils in vitro. Of
these, lemongrass essential oil possessed the most potent
anti-HSV-1 activity and completely inhibited viral
replication after incubation for 24 h, even at a con-
centration of 0.1% (Minami et al., 2003). Peppermint
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DOI: 10.1002/ptr
(Mentha piperita) essential oil exhibited high levels of
virucidal activity against HSV-1, HSV-2 and acyclovir-
resistant strain of HSV-1 in viral suspension tests
(Schuhmacher et al., 2003). The antiviral activity of the
oil was confirmed when the virus was pretreated with
the essential oil prior to adsorption. The essential oil
of Lippia junelliana and Lippia turbinate showed a
potent inhibition against Junin virus (Garcia et al., 2003).
Australian tea tree essential oil and to a lesser extent,
eucalyptus essential oil, demonstrated antiviral activity
against HSV-1,2 (Schnitzler et al., 2001). Both oils
affected the virus before or during adsorption, but not
after penetration into the host cell. The essential oil of
Santolina insularis showed an antiviral activity in toto
against HSV-1 and HSV-2 in vitro and was capable
of preventing cell-to-cell virus spread in infected cells
(De Logu et al., 2000). The oil directly inactivated virus
particles, thus preventing adsorption of virion to host
cells. Isoborneol, a common monoterpene alcohol,
showed dual virucidal activity against HSV-1 (Armaka
et al., 1999) and specifically inhibited glycosylation
of viral polypeptides. Unfortunately, no literature was
found concerning the antiviral applications of essential
oils against epidemic viruses such as HIV or hepatitis C
viruses, but the promising results illustrated here may
promote further investigations in this area.
Free radicals and other reactive oxygen species cause
oxidation of biomolecules including proteins, amino
acids, unsaturated lipids and DNA, and ultimately
produce molecular alterations related to aging, arterio-
sclerosis and cancer (Gardner, 1997), Alzheimer’s
disease (Butterfield and Lauderback, 2002), Parkinson’s
disease, diabetes and asthma (Zarkovic, 2003). The
human body is equipped with an inherent defense
system which can quench free radicals present in
almost all cells (Halliwell and Gutteridge, 1990). An
imbalance between free radical production and their
removal by the body’s antioxidant system leads to
a phenomena known as ‘oxidative stress’ (Abdollahi
et al., 2004; McCord, 2000). In this situation, an exter-
nal supply of antioxidants is necessary to regain a
balance between free radicals and antioxidants.
Essential oils, as natural sources of phenolic com-
ponents, attract investigators to evaluate their activity
as antioxidants or free radical scavengers. The essential
oils of basil, cinnamon, clove, nutmeg, oregano and
thyme have proven radical-scavenging and antioxidant
properties in the DPPH radical assay at room tempera-
ture (Tomaino et al., 2005). The order of effectiveness
was found to be: clove >> cinnamon > nutmeg > basil
oregano >> thyme. The essential oil of Thymus serpyllus
showed a free radical scavenging activity close to that
of the synthetic butylated hydroxytoluene (BHT) in a
-carotene/linoleic acid system (Tepe et al., 2005). The
antioxidant activity was attributed to the high content
of the phenolics thymol and carvacrol (20.5% and
58.1%, respectively). Thymus spathulifolius essential oil
also possessed an antioxidant activity due to the high
thymol and carvacrol content (36.5%, 29.8%, respec-
tively; Sokmen et al., 2004). The antioxidant activity of
oregano (Origanum vulgare L., ssp. hirtum) essential
oil was comparable to that of
-tocopherol and BHT,
but less effective than ascorbic acid (Kulisic et al., 2004).
The activity is again attributed to the content of thymol
and carvacrol (35.0%, 32.0%, respectively). Although
dietary supplementation of oregano oil to rabbits
delayed lipid oxidation, this effect was less than that
of supplementation with the same concentration of
tocopheryl acetate (Botsoglou et al., 2004). However,
when tested on turkeys it showed an equivalent per-
formance to the same concentration of
acetate in delaying iron-induced, lipid oxidation
(Papageorgiou et al., 2003).
The essential oils of Salvia cryptantha and Salvia
multicaulis have the capacity to scavenge free radicals.
The activity of these oils was higher than that of curcu-
min, ascorbic acid or BHT (Tepe et al., 2004). The
essential oil of Achillea millefolium subsp. millefolium
(Asteraceae) exhibited a hydroxyl radical scavenging
effect in the Fe3+–EDTA–H2O2 deoxyribose system
and inhibited the non-enzymatic lipid peroxidation of
rat liver homogenate (Candan et al., 2003). In addition,
Curcuma zedoaria essential oil was found to be an
excellent scavenger for DPPH radical (Mau et al., 2003).
The antioxidant activity of essential oils cannot be
attributed only to the presence of phenolic constitu-
ents; monoterpene alcohols, ketones, aldehydes, hydro-
carbons and ethers also contribute to the free radical
scavenging activity of some essential oils. For instance,
the essential oil of Thymus caespititius, Thymus
camphoratus and Thymus mastichina showed antioxi-
dant activity which in some cases was equal to that of
-tocopherol (Miguel et al., 2004). Surprisingly, the three
species are characterized by high contents of linalool
and 1,8-cineole, while thymol or carvacrol are almost
absent. The essential oil of lemon balm (Melissa
officinalis L.) shows an antioxidant and free radical
scavenging activity (Mimica-Dukic et al., 2004) with the
most powerful scavenging constituents comprising neral/
geranial, citronellal, isomenthone and menthone. Tea
tree (Melaleuca alternifolia) oil has been suggested as
a natural antioxidant alternative for BHT (Kim et al.,
2004) with the inherent antioxidant activity attributed
mainly to the
-terpinene and
content. Essential oils isolated from Mentha aquatica
L., Mentha longifolia L. and Mentha piperita L., were
able to reduce DPPH radicals into the neutral DPPH-
H form (Mimica-Dukic et al., 2003). The most powerful
scavenging constituents was found to be 1,8-cineole for
the oil of M. aquatica while menthone and isomenthone
were the active principles of M. longifolia and M.
It is clear that essential oils may be considered as
potential natural antioxidants and could perhaps be
formulated as a part of daily supplements or additives
to prevent oxidative stress that contributes to many
degenerative diseases.
Diabetes is a disease in which the body does not pro-
duce or properly use insulin.
Investigators have conducted few studies exploring
the potential benefits of essential oils as hypoglycemic
agents and publications on the subject are scarce. Some
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DOI: 10.1002/ptr
essential oils may aggravate diabetes: for instance,
rosemary essential oil showed hyperglycemic and
insulin release inhibitory effects in diabetic rabbits
(Al-Hader et al., 1994). Broadhurst et al. (2000) have
emphasized that the lipophilic fraction of aromatic
plants (i.e. essential oils) are not generally responsible
for any antidiabetic activity showed by these plants,
but Talpur et al. (2005) indicated that an oral adminis-
tration of a combination of essential oils including
cinnamon, cumin, fennel, oregano, myrtle besides
others, was able to enhance insulin sensitivity in type
2 diabetes, in addition to lowering circulating glucose
in the tolerance testing in rats. The essential oil of
Satureja khuzestanica resulted in significant decreases
in fasting blood glucose level in diabetic rats (Abdollahi
et al., 2003). More research is needed to confirm the
veracity of the hypoglycemic activity of other essential
oils and to elucidate their mechanism of action.
The oral and nasal routes are the most common non-
invasive paths for drug administration but are not
suitable for some drugs, either due to stomach acidity
or hepatic first-pass metabolism (Balfour and McTavish,
1992; Corson, 1993). Nasal delivery is often charac-
terized by poor absorption of lipophilic drugs (Orive
et al., 2003). Thus, the skin can present a promising
route for administration of drugs in a non-invasive way.
This phenomena is called topical or transdermal drug
delivery. The principle barrier to topical drug delivery
is the stratum corneum (SC) which is the outer most
layer of the skin. The permeability of the SC can be
increased by using skin penetration enhancers (Barry,
1991). Detailed reviews describing synthetic enhancers
are available (Williams and Barry, 2004; Ghafourian
et al., 2004).
Essential oils and their terpene constituents may
be acceptable natural alternatives to synthetic skin
penetration enhancers. They are characterized by their
relatively low price and promising penetration enhanc-
ing activities. The mechanism of skin penetration
enhancing activity of terpenes was postulated (Vaddi
et al., 2002; Higaki et al., 2003; Cornwell and Barry,
1994; Barry, 1991; Cornwell and Barry, 1991; Williams
and Barry, 1991; Williams and Barry, 1989). Due to
the popularity of these essential oils, their toxicities are
well documented (Opdyke, 1974–1976), and found to
be relatively low compared with most synthetic pen-
etration enhancers. The evaluation of the sensitization,
carcinogenicity and toxicity of these oils and their indi-
vidual terpene constituents are continuously carried
out by organizations such as the Research Institute for
Fragrance Materials (RIFM), International Flavor and
Fragrance Association (IFRA), Flavor Essence Manu-
facturers Association (FEMA) and the National Toxi-
cology Program (NTP).
Terpenes such as menthol and cineole were employed
as natural enhancers to improve the skin penetration
of propranolol, a
-blocker, which has a short biolo-
gical half-life and is subjected to extensive hepatic
first-pass metabolism (Amnuaikit et al., 2005). Cineole
and menthol are reported to improve the skin per-
meation of hydrophilic drugs better than other ter-
penes (Narishetty and Panchagnula, 2004). Menthol and
limonene produced maximum permeation of melatonin
along with traditional enhancers including fatty alcohols
and fatty acids (Kanikkannan et al., 2004). On the other
hand, menthol and menthone failed to enhance the
penetration of high-molecular-weight, lipophilic drugs
such as paclitaxel (Panchagnula et al., 2004). The
combination of two penetration enhancers of different
classes such as terpenes (e.g. cineole) and fatty acids
(e.g. oleic acid), synergistically enhanced transdermal
flux of zidovudine in addition to reducing lag time. On
the other hand, combinations of menthol with oleic or
linolenic acid did not enhance transdermal delivery
(Thomas and Panchagnula, 2003). The proper choice
of the terpene enhancer is dictated by the lipophilicity
or hydrophicity of the drug (El-Kattan et al., 2001).
Some essential oils themselves have been investigated
as potential skin penetration enhancers. Basil essential
oil showed an enhancing activity for accelerating
transdermal delivery of indomethacin (Fang et al., 2004).
The mechanism of action is probably due to the in-
creased skin–vehicle partitioning by the oils. Niaouli
essential oil showed a high activity for the permeation
of estradiol through hairless mouse skin in vitro (Monti
et al., 2002). In addition, eucalyptus and chenopodium
essential oils caused a near 30-fold increase in the
5-fluorouracil permeability coefficient (Williams and
Barry, 1989).
The word ‘aromatherapy’ combines two words: aroma
(a fragrance or swee smell) and therapy (a treatment).
Aroma and massage therapy are the practice of using
essential oils for psychological and physical well-being
via inhalation or massage.
The term ‘aromatherapy’ may be confusing to non-
specialists because it is used to describe a wide range of
practices involving odorous substances. Thus, massage
therapy, even when using essential oils, cannot be con-
sidered as aromatherapy. Only aroma delivery through
inhalation, to induce psychological or physical effects,
can be defined as aromatherapy (Buchbauer and
Jirovetz, 1993, 1994). Nevertheless, the clinical use of
essential oils and their volatile constituents via inhala-
tion or massage has expanded worldwide.
Inhalation of essential oils or their individual volatile
terpenes has a significant role in controlling the central
nervous system. For instance, aroma inhalation of Storax
pill essential oil and preinhalation of Acorus gramineus
rhizome essential oil are used in Chinese folk medicine
in the treatment of epilepsy (Koo et al., 2004; Koo
et al., 2003). The oils showed an inhibitory effect on the
central nervous system via the gamma-aminobutyric acid
(GABA)-ergic neuromodulation system. This effect
originates from the enhancement of GABA levels in
the brain (Koo et al., 2003). The fragrance compounds,
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DOI: 10.1002/ptr
cis-jasmone and methyl jasmonate, which characterize
the aroma of Jasminum grandiflorum have a tranquil-
lizing effect on the brain upon inhalation (Hossain
et al., 2004). They significantly increased the sleeping
time of mice induced by pentobarbital. This indicates
that these fragrant compounds were absorbed by the
brain and thereby potentiated the GABA receptor
response. Cedrol, which is a major component of
cedarwood essential oil, showed a sedative effect and
prolonged pentobarbital-induced sleeping time in rats
upon inhalation (Kagawa et al., 2003). The vapor of
lavender essential oil or one of its main components,
linalool, may contribute to relieving tension when
inhaled. They may also be applicable to the treatment
of menopausal disorders via inhalation (Yamada et al.,
2005). Lavender (Lavandula hybrida Reverchon
‘Grosso’) essential oil demonstrated an interesting
analgesic activity, mainly relevant after inhalation, at
doses devoid of sedative side effects (Barocelli et al.,
2004). In the field of complementary and alternative
respiratory medicine, inhalation of peppermint essen-
tial oil vapors has been suggested as an adjunct in com-
bined multidrug therapy in patients with disseminated
and infiltrative pulmonary tuberculosis. The action of
the oil is mainly due to the antimicrobial activity of its
volatile constituents (Shkurupii et al., 2002). Cinnamon
and clove oils also showed an inhibition to different
Gram (+)-ve and Gram ()-ve pathogenic bacteria from
the vapor phase (Lopez et al., 2005). Aroma inhalation
of lavender, peppermint, rosemary and clary-sage
essential oils can significantly decrease symptoms asso-
ciated with anxiety and stress. Inhalation of essential
oils can also modulate sympathetic activity in normal
adults: for example, the inhalation of pepper, estragon,
fennel or grapefruit essential oils resulted in 1.5- to
2.5-fold increase in relative sympathetic activity. In
contrast, fragrance inhalation of rose oil or patchouli
oil caused a 40% decrease in relative sympathetic
activity. On a hormonal level, inhalation of pepper oil
induced a 1.7-fold increase in plasma adrenaline con-
centration compared with the resting state, while inha-
lation of rose oil caused a 30% decrease in adrenaline
concentration (Haze et al., 2002). The rise in rat plasma
adrenocorticotrophic hormone caused by stress was sig-
nificantly reduced by inhalation of chamomile essential
oil (Yamada et al., 1996). The same effect can be
achieved by the intraperitoneal injection of diazepam,
a synthetic tranquillizer. The mode of action of Chamo-
mile essential oil is at least in part via benzodiazepine-
sensitive receptors, probably GABA. Other essential
oils also have sedative properties upon inhalation
(Buchbauer et al., 1992, 1993).
Inhalation of the volatile fractions of lavender and
monarda essential oils (0.1–0.2 mg/m3 air) reduced the
cholesterol content in the aorta and also atherosclerotic
plaques (Nikolaevskii et al., 1990), but had no effect on
the content of cholesterol in the blood.
Inflammatory diseases, such as allergy, rheumatism and
arthritis are often alleviated using essential oil massage
therapy (Maruyama et al., 2005; Lawless, 1997). Aller-
gic symptoms can be suppressed by tea tree oil (Brand
et al., 2002a; Koh et al., 2002), lavender oil (Kim and
Cho, 1999) and the volatile constituent, terpenene-4-ol
(Hart et al., 2000). This action is mainly due to the
suppression of histamine release (Brand et al., 2002b)
and cytokine production (Brand et al., 2001). Cutane-
ous delivery of geranium essential oil using massage
can suppress the inflammatory symptoms with neutrophil
accumulation and edema (Maruyama et al., 2005). A
lavender fragranced cleansing gel had a significant
transient effect of improving mood and making people
feel more relaxed (Field et al., 2005). Aromatic materi-
als, topically applied, showed positive effects on lung
mucus clearance in patients with chronic airway ob-
struction (Hasani et al., 2003). Even foot soaking in
warm water containing lavender essential oil followed
by reflexology treatment with jojoba oil containing
lavender, appeared to be effective for alleviating
fatigue in terminally ill cancer patients (Kohara et al.,
2004). Massage therapy using essential oil can be useful
in the treatment for people suffering from dementia.
The term ‘dementia’ is used to describe the symptoms
that occur when the brain is affected by specific dis-
eases and conditions, including Alzheimer’s disease,
stroke and other rarer conditions. Symptoms of demen-
tia include loss of memory, confusion and problems
with speech and understanding. Preliminary reports
have indicated positive effects of massage therapy
using selected essential oils for managing behavioral
and psychological symptoms in dementia. The essential
oil of Melissa officinalis (lemon balm) applied cutane-
ously in a lotion to patients with severe dementia was
found to be an effective treatment (Ballard et al., 2002).
The potential efficiency of massage therapy with essen-
tial oils to decrease agitation in patients suffering
dementia raise the question of whether inhalation of
the essential oil or its cutaneous delivery through
massage is responsible for the alleviative effect. Snow
et al. (2004) indicated that inhalation of lavender essen-
tial oil did not decrease agitation in severely demented
patients and a similar result had previously been re-
ported by Holmes et al. (2002). Cutaneous application
of the essential oil through massage may therefore be
necessary to achieve the alleviative effect in patients
with dementia.
Care should be taken when dealing with essential
oils in massage. Some essential oils have the potential
to be toxic (Prashar et al., 2004; Hayes and Markovic,
2003), while others initiate allergic reactions when
applied to the skin via massage (Veien et al., 2004;
Schnuch et al., 2004; Crawford et al., 2004; Maddocks-
Jennings, 2004; Scardamaglia et al., 2003; Mozelsio
et al., 2003; Bleasel et al., 2002; Vilaplana and
Romaguera, 2002; Romaguera and Vilaplana, 2000).
These allergic reactions arise from certain constituents,
e.g. benzyl alcohol, cinnamyl alcohol, eugenol, iso-
eugenol, hydroxycitronellal, geraniol and many others
(European Parliament, 2002). For this reason, warn-
ings must be printed on the label of essential oils
containing these components, and aromatherapy
practitioners and massage therapists should be also
aware of the potential for these adverse effects – and
be equipped to deal with them if they should arise
(Maddocks-Jennings and Wilkinson, 2004). At the same
time, physicians and other health professionals should
be able to differentiate between aesthetic applications
of odors and clinical uses of essential oils in order to
advise and better inform patients.
Copyright © 2007 John Wiley & Sons, Ltd. Phytother. Res. (in press)
DOI: 10.1002/ptr
10 A. E. EDRIS
This review attempts to shed light on the therapeutic
potential of essential oils and their aroma volatile con-
stituents in the prevention or therapy of disease. The
results reviewed in this article are aimed at attracting
the attention of researchers seeking new drugs from
natural products as well as those investigating the phar-
maceutical diversity of essential oils. The data presented
provide a basis for reviving the old art of ‘essential
oil therapy’ based on our modern scientific knowledge
of their mode of action, supported by safety issues
described here. Thus essential oils and their constitu-
ents can hopefully be considered in the future for more
clinical evaluations and possible applications, and as
adjuvants to current medications.
The author is indebted to Professor Gary Reineccius at the Food
Science and Nutrition Department, The University of Minnesota, for
his constructive opinions, his helpful notes and his support in English
language edition of this review.
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To advance the clinical development of thymoquinone (from Monarda) alone or in combination with chemotherapy agents for cancer therapy.
Full-text available
January 2011
    Essential oils have been important substances since early times. The review of its extraction methods and applications were treated in this study. These include hydrodistillation, hydrodiffusion, effleurage, steam distillation, cold pressing, solvent extraction, microwave assisted process and carbondioxide extraction. Its applications both the medicinal and therapeutics, such as aromatherapy,... [Show full abstract]
      Tea tree oil (TTO) comes from the leaves of Melaleuca alternifornia that belongs to the myrtle family (Myrtaceae). It is one of the most powerful immune system stimulants and sorts out most viral, bacterial and fungal infections in a snap, while it is great to heal wounds and acnes. In Vietnam, Melaleuca trees can grow on acid land that stretches in a large portion of lands in the Mekong Delta... [Show full abstract]
        Tea tree oil is an essential oil obtained by steam distillation of the leaves and terminal branches of Melaleuca alternifolia. In recent years, it has become popular as an antimicrobial agent against a large number of diseases. It is a natural substance that has a potential toxic effect especially if ingested. We report two cases of infants who came to our Emergency Department because they... [Show full abstract]
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