The Cropwatch Series

Cropwatch                                                No: 3b

OPINION: Methyl eugenol-containing essential oils.

© Tony Burfield May 2004

Worries about possible risks due to the methyl eugenol content of natural materials – herbs, essential oils - have surfaced in the recent past but there is a dearth of information on the subject directly available in the public domain to aromatherapists or complementary health practitioners. The following feature is an attempt to add some background information to this subject.

The warm, musty-mild-spicy odoured aromatic compound Methyl Eugenol (aka eugenol methyl ether, or 4-allyl-1,2-diomethoxybenzene)  is prohibited from being directly added as an ingredient to fragrances intended for retailed cosmetic products, due to worries about its’ potential carcinogenicity. 

As it occurs naturally in many essential oils and extracts, the addition of these ingredients is not restricted outright, but on provision that the methyl eugenol content does not exceed the following concentration in the following finished products according to the IFRA standards (see www.ifraorg.org/):

Fine Fragrances             0.020%*

Eau de Toilette              0.008%

Fragrance Cream           0.004%

Rinse off products          0.001%

Leave-on products/

Oral hygiene products 0.0004%

Non skin (as defined on IFRA website) 0.010%*. 

*The limit of 0.02% for the starred items applies to the concentration in the fragrance compound.

In effect this means that there is an obligation on ingredient suppliers, under the requirements of due diligence, to supply information to   customers, to make sure that they receive the necessary information in order for them to comply with the above requirements of the IFRA Standards. To spell this out in more detail, reporting the methyl eugenol content of the specific batch of the ingredient will then allow the customer to further calculate final levels of methyl eugenol appearing in the finished product. It is difficult to see how many small essential oil suppliers, without resort to internal analytical expertise, will be able to perform this function. Additionally, it is relatively easy to find plants for sale on the Internet, who’s essential oils contain high levels of methyl eugnol e.g. Black tea tree plants can be ordered at http://www.hotkey.net.au/~macs_oils/plant01.htm. No warning about the potential toxicity of methyl eugenol is presented.

It has long been established that methyl eugenol occurs in essential oils such as Canadian Snake root, Bay, Citronella, Laurel, Emodia, Fennel, Betel, “Brisbane Sassafras”, Pimento, Hyacinth etc., and its occurrence often coincides with the additional presence of eugenol (Poucher 1991). And so, purely as a guide, here below is presented a “snapshot” guide to the reported methyl eugenol content of several further essential oils. 

Published data on Methyl Eugenol Contents of Essential Oils.

1.    FEMA have published data to members on methyl eugenol contents of essential oils (no geographic origins specified).

2.    The BFA on 12.02.02 circulated BEOA data from 09.11.01 on the methyl eugenol content of a number of analysed commercial oils. Oils were classified by botanical name (no chemotypes were distinguished) and by origin.  There are no particular surprises, although methyl eugenol contents on rose otto seemed low-ish compared with other published data, and the range of methyl eugenol contents of the 23 basil oils (all apparently from Egypt) was relatively large. No data on fennel oil (identified by the EU Scientific Committee on Food as a dietary source of methyl eugenol) was included. The BEOA data document makes comment that expert analysis of genuine essential oils shows how widely essential oils vary in composition, and makes comment that the BACIS commercial data-base of essential oils shows methyl eugenol contents of 258 oils, that some of this data is misleading, and not representative of genuine high volume essential oils used in commerce.

3.    IFRA data on methyl eugenol contents of essential oils, as presented on the IFRA website http://www.ifra.org/ in May 2004 does not define the plant source species, the geographical origins of oils or any chemotype information. A document circulated by IFRA (to members only – not in the public domain – but most of the information the same as on the IFRA website) on April 6^th 2004 lists 21 essential oils, again giving no botanical identification, only giving geographic origins for two types of oils (citronella and rose), and giving chemotype information for basil only. As has been observed previously by this author, the standard of botanical reporting in IFRA documents, and in EU legislation leaves a great deal to be desired.

4.     A list of plants containing methyl eugenol, duplicating the species names of many of the entries below, can be found on the Agricultural Research Services data-base at http://www.ars-grin.gov:8080/npgspub/xsql/duke/chemdisp.xsql?chemical=METHYL-EUGENOL

Table I - Various References re: Methyl Eugenol content of EO’s.

N.B. Question marks in the above table appear when the author has had to make an intelligent guess at the botanical origin of the oil because the original source failed to reveal it.

Remarks on the Toxicity of Methyl Eugenol.

Similarities of methyl eugenol to the structure of safrole, a known carcinogen, have not gone un-noticed.

Following the RIFM/FEMA workshop in May 2000, the FEMA expert panel issued a report entitled “Safety Assessment of Allylalkoxybenzene Derivatves Used as Flavouring Substances – Methyl Eugenol and Estragole”. This included a description of the 2-year bioassay with methyl eugenol by the National Toxicity Program (NTP) whose aim was to establish the carcinogenic potential of methyl eugenol regardless of route of administration. The NTP study found that the present exposure to methyl eugenol from food (mainly intentional addition of essential oils, spices and spice isolates) presents no hazard to human health. The report finds that although very high doses are carcinogenic, they are such that they must have first induced a hepatotoxic effect. We also subsequently learned from the RIFM/FEMA workshop write-up, that one serving of pesto contains from 10-100 times the average daily human consumption of methyl eugenol, although even this level was 100 times lower than the lowest dose forcibly given to animals in the NTP assay.

The NTP technical study on the 2 year toxicology and carcinogenisis studies on methyl eugenol in F334/N rats and B6C3F₁ mice was published in July 2000. It showed clear evidence of carcinogenic activity of methyl eugenol in the tested rodents, and can be viewed at http://ehis.niehs.nih.gov/ntp/docs/tr491/tr491abs.pdf

The German Bundesrat decided on May 11^th 2001 not to market flavourings and foodstuffs containing added methyl eugenol (or methyl chavicol) after June 30^th 2001, although this ruling did not apply to methyl eugenol naturally present in flavourings or foodstuffs.

The EU’s Scientific Committee on Food expressed an opinion on methyl eugenol on 26.09.01, which can be viewed at http://europa.eu.int/comm/food/fs/sc/scf/out102_en.pdf The committee remarked that methyl eugenol is a multi-site, multi-species carcinogen, being both genotoxic and carcinogenic. Average human intake from diet of methyl eugenol amounted to 13 mg/person/day and the 97.5th percentile was 36 mg/person/day (on a body weight basis these values correspond to 0.19 and 0.53 mg/kg bw/day, respectively). The committee was unable to establish a safe exposure limit.

Subsequently IFRA decided to severely restrict the limits of methyl eugenol in finished fragranced products in 2001 (36^th Amendment to the Code of Practice).

Low methyl eugenol rose oil has been commercially offered by a small number of aroma houses. Removal of the methyl eugenol content by high vacuum fractional distillation seems to adversely affect the typical rose character in products offered. Removal of the methyl eugenol content by spinning band or spinning cone distillation may be more satisfactory, but production time is at a premium on this expensive technology. Rose oils naturally very low in methyl eugenol are known in Eastern Europe and further East, but the quality is very poor to actually unacceptable for most purposes, even before methyl eugenol removal.

As a closing comment, it is hard to see why the aromatherapy and cosmetic industries are “led by the nose” on the choice of available commercial rose qualities utilised, which merely reflect historical perfumery trade uses. It has previously been established that rose absolutes from varieties of garden roses can demonstrate beneficial cosmetic properties (Étienne et al. 2000) whereas a conventional commercial rose absolute showed none of these effects. Further, it is likely that certain of these other varieties will only present a fraction of the methyl eugenol levels encountered in conventionally sourced rose ottos and absolutes.

Methyl Eugenol in Aromatherapy.

The author is unable to find any detailed advice given by professional aromatherapy organisations to members on this issue, on a par with that put by IFRA for its membership in the perfumery profession. Harris (2002) has reviewed the position of methyl eugenol in aromatherapy practice in the light of IFRA restrictions in the fragrance industry. It is worth exploring a number of points.

Firstly, Harris notes that the IFRA have published a list of essential oils (e.o.’s) with methyl eugenol contents, commenting that these figures only pertain to oils used in the fragrance industry. Harris instead quotes e.o. data from Lawrence (1998-2002). However IFEAT have previously criticised the use of Lawrence’s data (specifically over the separate 26 allergens issue), as they maintain it is relates only to experimental data and does not relate to the composition of commercial oils. In any case, in the real world, the e.o.’s distributed by many (but certainly not all) aromatherapy oil suppliers are identical to those distributed by the fragrance industry.

Harris further maintains that “the average aromatherapy treatment regime consists of 5-10 sessions, given at most once per week, generally with the essential oils employed being changed during this regime according to the improvement of the client…”, and goes on to state, “those most at risk from methyl eugenol are the aromatherapists themselves”, but does not investigate exposure of this most “at risk” group in any satisfactory detail. Harris further mentions avoidance of high methyl eugenol containing oils by therapists, and talks of using “3 drops in a blend” – which, as several professional therapists have privately commented, “is not  Aromatherapy”.

Since aromatherapy is a poorly paid profession, many professional aromatherapists are obliged to work extended hours, and may have to perform 6-8 massages per day, 5-6 (or more) days per week. Further, a whole body massage may well be carried out with 20-50 mls of massage oil containing 2-2.5% e.o., although some practitioners apparently have been known to use even higher concentrations (Guba 1998). Unknown amounts of methyl eugenol are therefore absorbed by the therapist throughout the week, via skin absorption through the hands, and by inhalation of vapour. Harris doesn’t mention the fact that diet is additionally adding to the therapist’s body burden of methyl eugenol.

The above factors may eventually allow a more realistic calculation of daily human body loading from methyl eugenol for aromatherapists, but interpretation of the data revolves around interpretations of the NOEL (no-effects) level in the longer-term and appropriate safety factors (IFRA used a factor of 1000 X).  Since aromatherapeutic treatments such as whole body massage are vastly different from animal dosing studies, drawing direct conclusions about possible toxicological effects is distinctly risky. Further, it is already known from human liver microsomal preparations that metabolism rates by human cytochrome P450 isozymes for methyl eugenol varies more than 37-fold (Gardner et al. 1997) suggesting a wide range of serum concentrations will occur in the general population following methyl eugenol exposure.

Meanwhile Schecter et al. (2004) have produced a study on human consumption of methyl eugenol and its elimination from serum under a mandate from the National Toxicology Program of the US Department of Health and Human Services. In particular the team investigated the consumption of methyl eugenol from a brand of gingersnaps, found to contain a relatively high concentration of methyl eugenol at 3.3mg/g (a number of other foodstuffs containing lower concentrations of methyl eugenol are also listed in the article & cigarette tobacco’s were identified as another possible source of methyl eugenol exposure!). Serum peak levels of methyl eugenol were found to be within range of a concurrent study of 213 non-fasting subjects in the third Nutrition Examination Survey (NHANES III, 1988-1994). However in this latter study, the authors found that methyl eugenol levels in the blood of the general US population were higher than expected (but the highest concentration found, 390pg/g, was still 2000 X lower than the lowest dose used in the NTP rodent studies referred to above). Nevertheless, as Schecter et al. remark, the significance of the elevated levels with respect to any toxicological consequences, still remains to be determined.

It may well eventually turn out that a working aromatherapist, constantly using basil and rose oils, and with a fondness for pesta and flavoured cigarettes is more likely to be hit by a meteorite than to contract a toxicological problem due to daily methyl eugenol exposure from all these routes. Its just that it would be nice to think that those entrusted with a duty of care towards working people in our society were actively investigating this topic. The situation being as it is, assessments on this topic are more likely to be made by self-educated laymen, than by formerly qualified toxicologists – and to this end, Cropwatch has written to some toxicologists for some learned opinions on this matter. Any replies will be published in further editions of this organ.

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BFA: British Fragrance Association

IFEAT: International Federation of Essential Oils and Aroma Trades

IFRA: International Fragrance Research Association

Table Data References:

Aurore, G. S. Abaul, J. Bourgeois, P. Luc, J. (1998) “Antibacterial and  Antifungal Activities of the Essential Oils of Pimenta racemosa var. racemosa P. Miller (J.W. Moore) (Myrtaceae).” J. Essential Oil Res. 10(2), 161-164.

BEOA: British Essential Oils Association 9^th Nov 2001 – data reproduced by kind permission.

Brophy JJ: Brophy JJ (1999) “Potentially Commercial Melaleucas” in Tea Tree – the Genus Melaleuca eds. Ian Southwell & Robert Lowe. Harwood Academic Publishers.

Brophy et al: Brophy et al. (1999) J Essen Oil Rec 11, 327-332.

Duke: Duke J (?) from Chemicals and their Biological Activities in: Peumus boldus MOLINA (Monimiaceae) – Boldo – see http://www.rain-tree.com/db/Peumus-boldus-phytochem.htm

Duke 2 : see http://www.ars-grin.gov:8080/npgspub/xsql/duke/chemdisp.xsql?chemical=METHYL-EUGENOL 

EOS:  “Essential Oil Safety” Robert Tisserand & Tony Balacs Churchill-Livingstone 1996.

F & P: Franchomme P. & Peneol D (1995) “l’Aromatherapie

Exactement” pub. Jollois. R.

Guba R (1998) “Toxicity Myths –the Actual Risks of Essential Oil Use.” Centre for Aromatic Medicine 1998.

IFRA website: www.ifra.org information as at 01.05.2004

IFRA: Annex 1 IFRA Standards.doc April 6, 2004.

IS: Ian Southwell (1999) “Tea Tree constituents” in  Tea Tree – the Genus Melaleuca eds. Ian Southwell & Robert Lowe. Harwood Academic Publishers

Kam: Kameoka H. (1993) “The Essential Oil Constituents of Some Useful Plants from China” in Recent Developments in Flavour & Fragrance Chemistry –Proceedings of the 3^rd Int. Haarman & Reimer Symposium Pub. VCH NY 1993.

Lawr.: Lawrence BW (1989) EO’s 1981-7 Allured Publ. 

Lawr. a: Lawrence BM et al. (1985) Perf & Flav 10(6), 56-58 Dec 1985-Jan 1986

Mazza G. (1983) “GCMS Investigation of Volatile Components of Myrtle Berries” J. Chromatog. 264, 304-311.

SCIB: Zhu Lianfeng et al. (1993) Aromatic Plants & Essential Constituents South China Inst of Botany, Hai Feng Publishing Co.  

Shiva et al: Shiva MP, Lehri A, Shiva A. (2000) Aromatic & Medicinal Plants pub IBD 2000.

TB: Tony Burfield (2000) Natural Aromatic Materials: Odours and Origins pub. AIA Tampa.

TB see: http://www.users.globalnet.co.uk/~nodice/new/magazine/odprofile.htm

TBb: Tony Burfield (unpublished data)

TBc: Tony Burfield & Sylla Sheppard-Hanger (2002) “Basil Oils Monograph” AIA UK 2002.

TQ: trade suppliers questionnaire (IFF 2003)

Poucher (1991) Poucher’s Perfumes, Cosmetics and Soaps - Vol 1 The Raw Materials of Perfumery 9^th edn. Blackie Academic & Professional.

Zhu Liangfu et al. (1993) Aromatic Plants & Essential Constituents South China Inst of Botany.

Text References.

Étienne et al. (2000) “New and unexpected cosmetic properties of perfumes. Effects upon free radicals and enzymes induced by essential oils, absolutes and fragrant compounds.” International Journal of Cosmetic Science 22, 317-328.

Gardner et al. (1997) “Cytochrome P450 mediated bioactivation of methyleugenol in Fisher 344 rar and human liver microsomes.” Carcinogenesis 18, 1775-1783.

Harris B. (2002) “Methyl eugenol – the current bete noir of aromatherapy”. Int. J. of Aromatherapy 12(4), 193-201.

Lawrence B.W. Progress in Essential Oils (1998-2002).

NHANES III 1988-94 National Centre for Health Statistics (1994). Plan and Operation of the Third National Health & Nutrition Examination Survey, 1988-94. Series 1: Program & Collection Procedure No 32.

Schecter A et al. (2004) “Human Consumption of Methyleugenol and Its Elimination from Serum” Environmental Health Perspectives 112(6), 678-680.