By Ron Guba
In the wide variety of Aromatherapy books and
periodicals available today, we find many recommendations regarding the safe,
therapeutic use of essential oils, often contradictory and seldom supported
by either references, research or actual clinical experience.
In this presentation, I will explore the range of recommendations made and address
the validity of each, especially addressing the underlying assumptions and reasons
for these statements.
I have personally been involved in the both the practice and the business of
Aromatherapy since arriving in Australia in 1986. Having always approached the
therapeutic use of essential oils from the "radical" French "Aromatic
Medicine" perspective, I have long noted the many incongruous and exaggerated
statements regarding essential oil toxicity.
Over these past twelve years, through my involvement with various government
and industry bodies, I have specifically focused on this topic of essential
oil toxicity as one area of study, given the potential "poisons scheduling"
of various essential oils by the Australian National Drugs and Poisons Scheduling
Why is there such a diversity of opinion regarding
essential oil toxicity?
Three reasons appear to me outstanding - that
of "philosophical" differences, the lack of knowledge amongst practitioners
and authors and the fear of public misuse.
Utilising Dr. Daniel Pénöel's
concept of the "Aromatic Tryptic" (1), we can
characterise "Holistic" Aromatherapy as fundamentally "energetic"
in nature. Encouraged by the work of Maugerite Maury in France during the 1930's
(2), this approach has become the dominant form of Aromatherapy
practiced in English-speaking countries.
Employing relatively low dosages of essential oils (generally 2.5% or less in
massage applications), the majority of therapeutic effects noted appear to be
primarily of a secondary "energetic" or "terrain" nature,
as in the case of acupuncture or homeopathy, for example, as well as working
via the olfactory sphere. Actual physical doses of essential are 'ingested'
via Aromatherapy massage treatments, but the dosages are quite small, perhaps
on average from 50 to 75mg.
"Holistic" Aromatherapy originally developed primarily in the domain
of beauty therapy. Practitioner training, even up to the present day, has tended
to concentrate more on massage and other application methods, than on an in-depth
understanding of essential oils from both the chemical/pharmacological viewpoint
and their full history of use in traditional medicine.
M. Maury also stated her own preference to avoid the more "medical"
applications of essential oils, including internal use. Such applications, she
felt were best left to medical practitioners. (3)
Following from M. Maury, the growth of "Holistic" Aromatherapy continued
primarily in England by those influenced by her, such as Marceline Arcier and
Developing from the domain of beauty therapy, we can see a particular "dogma"
has evolved, one that is "gentle" and oriented from an "energetic"
perspective towards both "low-dose" applications and the avoidance
of internal and other "high-dose" applications.
As such, I suggest that this particular bias has served as the "philosophical
base" on which many of the common statements regarding essential oil toxicity
In contrast, we can say the French "Aromatic Medicine" approach that
has developed most strongly amongst French medical practitioners (as well as
naturopathic and herbal medicine practitioners) since R. M. Gattefosse's work
in the 1930's, is more of a "physical" approach.
This "French" approach often utilises comparatively high doses of
essential oils both topically and internally, to realise dose-dependent pharmacological
This discipline relies on a greater understanding of the chemical structure
and the pharmacological/toxicological effects of essential oils, to suggest
safe dosage levels and contra-indications for use.
I can therefore suggest that such dosage recommendations represent a more realistic
view of the safe uses and potential toxicity of essential oils for all practitioners.
As I have mentioned above, "Holistic"
Aromatherapy training has not generally taken into account any in-depth training
in either the chemistry or known pharmacology of essential oil compounds.
As such, we can notice that many of the dosage recommendations and contraindications
mentioned in Aromatherapy literature are based on an incomplete or limited understanding
of the issues involved.
What can be noted in many publications are statements that are based on the
"If I do not know about the possible negative
effects of an essential oil, then, if any possible negative effect might be
noted, I'm going to recommend that people not use such oils at all or else in
very tiny amounts".
To err on the side on caution may be considered
laudable. However, we can notice that such exaggerated statements has led to
a common perception that the therapeutic use of essential oils can be an extremely
risky proposition, even amongst those who are purported to be highly qualified
It is my premise, that those who would call themselves Aromatherapists should
be the most qualified in the actual uses and the potential toxicity of essential
oils, as we would expect those with either medical training (with pharmaceutical
drugs) or medical herbalists (with herbal preparations) to have with their common
The vast majority of Aromatherapy books are
written for the lay public. In this regard, care is taken to recommend dosages
and essential oils that will neither create negative reactions or lawsuits.
Hence, dosages are kept extremely low and any essential oil that might be construed
to have any possible negative effect, such as during pregnancy, is routinely
advised to be best left alone.
If we inspect such books, we also find that these publications, easily accessible
to the public, are often used as "textbooks" in Aromatherapy practitioner
training. If we observe further, we also find that many publications offered
for practitioners and health professionals make many of the same recommendations.
Why is this? I suggest that "Aromatherapy" still needs to go beyond
being just a "good feeling", fad therapy. As with the standards that
have developed relative to the training and practice of medical herbalism, Aromatherapy
demands a level of practitioner training that is comprehensive in it's scope
and knowledgeable in all the effects of essential oils - both positive and potentially
Essential Oils and Toxicity Issues
As with most medicinal drugs, whether of a "synthetic"
or a "natural" origin, the compounds present in essential oils have
the potential to create serious, even fatal toxic effects, if ingested in overly
There are numerous cases reported in toxicological literature regarding both
serious (non-fatal) and fatal outcomes of essential oil ingestion in both children
These cases are generally due to accidental ingestion by young children, attempts
at creating abortions in past years and the use of essential oils for suicide
attempts. There are more rare cases of toxic effects due to overly large doses
of specific essential oils being "self-prescribed", "prescribed"
to children by parents or prescribed to clients by ill-informed therapists.
Most essential oil compounds have a "non-specific" toxic effect, whereby
the absorption of these lipophilic compounds into cellular membranes can eventually
lead to disruption of membrane permeability. The primary toxic outcome is that
of the disruption of ion channel function in nerve cells, first affecting the
heart and central nervous system, leading to cardiac and respiratory depression.
To create such effects, however, require huge dosages, in the order of 300mL
Certain aromatic compounds, most notably 1,8 cineole (as in many Eucalyptus
species), camphor (borneone) (as an isolated compound or as in Rosmarinus officinalis
CT camphor and Lavandula latifolia) and methyl salicylate (as a synthetically
derived compound or as in Gaultheria procumbens) have specific toxic effects
at much lower doses. These compounds make up the bulk of both serious and fatal
poisonings in children and adults, due not just to their toxicity, but to the
common availability of products containing these compounds and their reputed
beneficial properties. (5)
Given the rapid and almost complete absorption of essential oils ingested orally,
this route of administration has the highest potential for toxic effects.
First aid measures for ingestion of significant amounts of particularly toxic
essential oils (such as more than 2mL of high-cineole Eucalyptus oils in young
children) is straightforward: take the child to the nearest hospital emergency
room or at least call or a Poisons Information Centre for instructions. The
vast majority of accidental essential oil ingestion in children results in few,
if any symptoms and resolve safely with no medical intervention.(6)
It is often difficult to determine just how much of an essential oil (or any
product) a young child has ingested. If toxic symptoms do begin to develop,
gastric lavage, hemodialysis and other supportive medical measures may well
be necessary. To attempt to either dilute the stomach contents by giving burnt
toast (or activated charcoal), milk or other foods or to try to induce vomiting
is not recommended. Either approach, if vomiting occurs, has the potential to
allow these volatile compounds to enter the lungs, potentially creating aspiration
"Aromatic Medicine", or the use of essential oils as ingested herbal
medicines by trained physicians and complementary therapists, has not been responsible
for any severe cases of toxicity. As with any "drug", if an appropriate
dose is used (with essential oils, this is often in the range of only 100 to
300 mg per day), toxicity is not an issue.
In the case of the more common practices in Aromatherapy, we are speaking of
topical applications - in the form of essential oil preparations used in massage
treatments, in baths, etc. or in the form of "low dose" inhalations.
Such applications have not created any acute or chronic systemic toxicity -
the amounts absorbed into the body and the dosages used are far too low.
'Lethal Dose' Tests and Essential Oils
The most common test of potential human toxicity
is that of the "LD50" test or the "median lethal dose".
This test is routinely applied to laboratory animals (humans do not usually
volunteer) in the testing of compounds used in pharmaceuticals, agricultural
chemicals, flavours, fragrances and cosmetics, to name a few.
In this testing procedure, laboratory animal are given measured doses of compounds
until approximately half of the test population die. The "median dosages"
are then generally given in the ratio of milligrams or grams of test compound
per kilogram of bodyweight.
Hence, a LD50 rating of 1.0 represents that 50% of the test animals died on
a dosage of 1 gram per kilogram of body weight. If we consider ourselves to
be large rodents, this would translate to 60 grams of a particular compound
would be the likely lethal dose to an adult weighing 60 kilograms.
We should consider (outside of ethical considerations - but no effective substitute
has yet to be found) that such tests generally are based on either acute oral
(by mouth) or injected lethal doses.
This means that the LD50 dose represents the median toxic dose taken all at
one time, either by ingesting or by direct injection of the test compound.
There are also LDLo values used. This figure represents the lowest dose of a
given compound that has caused death. LDLo values are often assigned when the
number of test animals used is small.
As well, since there have been human fatalities caused by the ingestion of various
essential oils or isolated aromatic compounds, we can sometimes approximate
a LDLo value for humans, if a reasonable idea of how much of a particular compound
was ingested is known.
Chronic (long term) toxic doses and dermal (high-dose topical applications)
have also been studied with laboratory animals. Toxic chronic doses are generally
less than the corresponding acute dose. Long term studies are often carried
out for 90 days of exposure, to detail whether or not a particular test substance
has a cumulative toxicity. If it does have a cumulative toxicity, this will
be seen by a lower daily dose being required to demonstrate toxic effects or
death, than the acute LD50 dose required in one application. There are few results
available for chronic toxicity of essential oils, but studies from 1959 suggest
a dose range from 5 to 10 times less than an acute toxic dose. (8)
Dermal studies performed on rabbits have produced conflicting results that do
not appear to be terribly relevant to human exposure. One reason appears to
be the greater permeability of rabbit skin to the passage of different compounds,
as compared to human skin. There are some reports of lasting skin damage in
humans, such as due to the spilling of undiluted Clove oil onto the skin and
to the chronic application of a concentrated methyl salicylate preparation (covered
with a heating pad).(9,10)
However, I have seen no reports to date of any fatalities via topical application
of essential oils; fatal outcomes are due to excessive ingestion of specific
The Mistakes in Applying LD50 Values to Aromatherapy
In terms of the most common uses of essential
oils in Aromatherapy, it is the acute LD50 dose that is most relevant in this
consideration. This is considering therapists using essential oils on their
clients and preparing formulations for the client to use outside of visits.
Animal LD50 values can be a useful guide to potential essential oil toxicity
when we are considering the acute toxicity of essential oils, such as Wintergreen
(mostly methyl salicylate) or Eucalyptus species (those with a high 1,8 cineole
For example, an essential oil, such as Thuja (Thuja occidentalis), with an animal
LD50 rating of 0.83, would translate to approximately 50 grams being a median
lethal dose for an adult weighing 60 kilograms.
Of course, this would be a huge dose and severe toxic effects would still be
seen (and have been) at lower doses like 10 grams.
The point to make is again, the values we are considering here are based on
acute oral toxicity, that is, the lethal dose that would be ingested all at
There are two areas where mistakes relative to Aromatherapy "toxicity statements"
Dosages: Essential oil dosages,
such as applied in preparations for massage, in baths or for inhalations (or
simply to fragrance an environment) are generally of a minute fraction of the
acute toxic dose (and of the chronic dose as well).
Let us take Wintergreen oil as an example. The acute oral rat LD50 is 1.2. In
humans, however, methyl salicylate does appear to be more toxic. Given the numbers
of fatalities in years past, with the amount ingested being known in a number
of cases, we can estimate a human LD50 of 0.3. For a 60kg adult, this would
translate to the ingestion of about 18 grams. (11)
Now, let us say that we want to apply a 2.5% dilution of Wintergreen oil to
our sore lower back. We then apply 1 mL of this preparation
1mL x 2.5% = approximately 0.025 grams of methyl salicylate.
0.025 gms ÷ 18 gms (LD50 dose) = 0.00139 or 0.139%.
Hence, the applied dose is only 0.139% of the median lethal dose.
This is more than 700 times less.
Of course, if we increase the amount applied of the 2.5% formula,
we increase the dosage received. Hence, if we applied 10mL of the formula all
at once, the dose would now be 0.25 grams or 250 milligrams. Putting this into
perspective, even if the methyl salicylate was totally absorbed, this dose would
represent the same amount of salicylate compounds as found in one tablet of
Wintergreen and Sweet Birch essential oils are routinely mentioned as oils to
avoid in Aromatherapy, even for trained practitioners. Members of the International
Federation of Aromatherapists take a "vow" not to use Wintergreen
essential oil. (12)
Yet, we have the strange contradiction of many methyl salicylate-containing
topical products (containing from 10% to 30% methyl salicylate) being readily
available to the untrained public - with few negative side-effects reported
(methyl salicylate, even used topically, is reasonably contraindicated in people
taking the anti-coagulant drug, warfarin). (13)
Even with this relatively toxic compound (as I would suggest that any essential
oil with an LD50 of less than 1.0 is), an effective anti-inflammatory preparation
can be used with no acute toxic effects.
Method of Application
Not only should we consider the dosage given,
but also account for how the essential oil is applied.
We can say that when an essential oil is orally ingested, it is fully absorbed
into the portal blood circulation. However, other types of applications do not
represent the same level of absorption and dosage.
The following chart details the potential toxicity of each method of application.
This accounts for both the amount of absorption as well as the amount of the
typical doses given.
Mode of application - Comments
Oral ingestion - Assume full absorption of dose.
Topical Preparations - If left unoccluded, conservatively less than 50%
of the applied dose would be absorbed.For the application of 10mL of a 2.5%
EO concentration, absorbed dose would be less than 100mg
Vaginal Pessaries - A typical 3 g pessary at 10% EO concentration would
represent 300mg total if full absorption is acheived
Rectal Suppositories - A typical suppository (1 to 3 g) would contain
250mg or less, which would represent total dose if full absorption is achieved.
Inhalations - Considering an aerosol diffuser that dispenses 1.0mL of
EO per hour: a typical adult inhalation session of 15 minutes, with less than
40% inhaled and absorbed equates to a dose of less than 125mg.
In this light, we can then understand why the relatively toxic essential oil
of Pennyroyal, could be used as a safe addition as a mucolytic used in an inhalation.
With inhalations, absorption is quite high, but the typical dose is small.
With topical applications, we cannot assume full absorption of applied essential
oils. If we do not occlude (or cover) the site of application, as is generally
the case with topical Aromatherapy applications, the dose is significantly lessened
One American study found that 75% of an applied dose of various fragrance compounds
were absorbed through human skin when the skin was covered after application.
When the skin was left uncovered, the total amount absorbed dropped to only
It is clear that topically applied essential oils will penetrate the epidermis
of the skin. However, it is an area that still requires further research to
understand how a variety of different factors (such as the type of essential
oil compounds, the excipient or "carrier" base used, temperature,
age of the skin and on) affect the amount absorbed through the skin.
Available studies suggest a wide range of absorption amounts. d-limonene, the
major constituent of most citrus oils, was demonstrated to only have an absorption
rate of 2.0% when applied to human tissue samples. (15)
A 2.0% dilution of True Lavender (Lavandula angustifolia) oil applied to the
abdomen of a volunteer, showed that approximately 10% of the Lavender oil was
absorbed into the general blood circulation, showing a relatively rapid absorption
rate that peaked 20 minutes after application. After 90 minutes, both linalool
and linalyl acetate (the compounds tested for) had dropped almost to zero, showing
almost complete biotransformation and excretion. (16)
Some compounds found in essential oils have relatively high absorption rates,
even on unoccluded skin, such as coumarin (46% absorption ) and cinnamic aldehyde
Lastly, a study testing percutaneous absorption with rhesus monkeys, tested
three compounds, benzyl alcohol, benzyl acetate and benzyl benzoate (all naturally
occurring in Ylang Ylang essential oil, for example).
When applied in a moisturising lotion base, with the skin uncovered, the total
absorption rate varied from approximately 20% for benzyl acetate, up to 70%
for benzyl benzoate. (18)
The assumption here is that essential oils and like compounds are more easily
absorbed through the hair follicles than just the stratum corneum or "horny
layer" of the skin. Hence, it can be theorised that monkey skin, covered
in hair follicles, would more efficiently absorb essential oils.
Taking the available research into account it would be fair and conservative
to state the following when figuring the absorbed dose of an essential oil applied
to unbroken skin in some form of an excipient or "carrier" (vegetable
oil, cream, gel, etc.) and left uncovered:
Only up to 50% of a topically applied dose is
Hence, in the Wintergreen oil example given
above, instead of the low amount of 0.025 grams being absorbed, the amount can
be figured at half that value, or 0.0125 grams - less than 1400 times the median
toxic oral dose.
This covers both the typical applications applied in Aromatherapy treatments,
as with massage, as well as topical OTC preparations, such as methyl salicylate
containing "liniment" products.
However, in the case of broken skin, where the stratum corneum is compromised
or not present (as in wounds, burns and various forms of dermatitis), it would
be more prudent to figure a 100% absorption of applied essential oils.
"It's all dose-related"
Therefore, we can look at a number of the essential
oils mentioned in Aromatherapy books "never to be used in therapy",
such as Hyssop, Pennyroyal, Tansy, Thuja, Wintergreen and Wormwood for example.
We can understand, however, that such essential oils can be used safely, if
one respects the dose given and the method of application used.
There is certainly an argument against having essential oils with a high, specific
toxicity easily available to the public. However, we are considering here the
discriminative use of essential oils by therapists that should be trained in
the details of appropriate dosages and applications.
Essential Oils and Cancer
Also found in many books are statements regarding
the non-use of essential oils containing compounds that have been shown to promote
carcinogenesis in animal studies and various cell assays. I have written a separate
paper on this topic (Toxicity Myths - Essential Oils and Cancer) and will present
a summary here.
Two compounds in particular, A- and b-asarone as found in various cultivars
of Acorus calamus and in Guatteria gaumeri and safrole (the major constituent
of Sassafras albidum and Oceotea pretiosa essential oils), have already been
effectively banned (only tiny dose levels are permitted in foods) by various
governmental 'food and drug' agencies around the world, due to the demonstrated
carcinogenic effects in laboratory animals. Hence, these are not essential oils
would ever be widely used by therapists nor will OTC products for therapeutic
use be made.
However, using Calamus as an example:
Dr. Rudolph Weiss, a respected German physician who taught herbal medicine up
until the 1980's, states in his book, Herbal Medicine regarding Calamus, "
At the same time it should be noted that Calamus has been widely used since
antiquity and is still much used today, and there have been no reports of cancer
developing after it was taken. It is important not to attach excessive importance
to such experimental studies.
Where Calamus is concerned, there clearly
is no need for concern if the drug is used for medicinal purposes and for a
limited period only." (20)
A- and b-asarone have been found to be carcinogenic in rodents at elevated levels.
As is the common case, we find that large doses are fed to lab animals to elicit
hepatic cancers. Dosages as high as 50mg/kg per day (about 3 grams of Calamus
oil for an average adult) in rats showed no toxicity or genotoxicity. 25 Dosages
as high as 5mg/kg of a-asarone showed no embryotoxicity or teratogenecity (birth
defects) in the embryos of pregnant mice, and doses as high as 20mg/kg, did
not alter either sperm count in male mice nor create germinal mutations in male
or female mice. (21, 22)
These are much larger doses than would be had by therapeutic ingestion of Calamus
herbal preparations or topical application of Calamus essential oil.
At the same time, asarone and the herbs containing it, are being studied for
a strong cholesterol-lowering effect, as well as a diverse range of other effects
- tranquillising, sedative, anti-ulcer, anti-spasmodic, anti-carcinogenic, for
the treatment of gallstones and more. Calamus has a sterling reputation as a
powerful stomach tonic, being an excellent appetite stimulant, as in the case
of treating anorexia. (23, 24, 25, 26, 27, 28)
One can reasonably suggest that the effective 'banning' of a herb such as Calamus,
is indeed a case of 'overkill' by regulatory agencies.
Two other compounds found in essential oils, estragole (or methylchavicol) and
methyleugenol have been demonstrated to have weak genotoxic and carcinogenic
At this time, no governmental body has taken any step to limit or ban these
compounds in foodstuffs or consumer products, given the low potential for harm.
Nevertheless, this has led to various Aromatherapy authors giving their opinion
that therefore the essential oils of 'Exotic' Basil and Tarragon (rich in estragole)
and Melaleuca bracteata (rich in methyleugenol) should not be used at all in
Aromatherapy practice. (29, 30)
From Toxicity Myths - Essential Oils and Cancer: