3 (Part I) Quality and safety
The dangers of essential oils have often been exaggerated, usually based on insufficient evidence and inappropriate comparisons. This chapter shows that these powerful substances, used knowledgeably and with due caution, pose no threat to health. The highest possible quality of medicament is always required in therapy, and this chapter shows that aromatherapy is no exception to the rule. The main chemical groups found in essential oils are outlined, along with an account of methods of testing for quality.
Despite this good record, statements are sometimes made which sensationalize aromatherapy or exaggerate unwanted effects of the oils. More to the point would be to educate both the supplier and the general user in the appropriate and safe use of essential oils. That way lies a safe and sound future for the popular use of aromatherapy.
The food industry is the greatest user of essential oils, where they are used at low levels as flavourings and when used in this way there are none that could be expected to pose any significant risk to health (Adams & Taylor 2010). Chronic studies using animals, sponsored by the National Toxicity Program, have been performed on more than 30 major components of essential oils at much higher intake levels than the daily intake dose, and the majority showed no carcinogenic potential (Smith et al. 2005). Obviously, when consumed in higher quantities some plant extracts do exhibit toxicity, e.g. hemlock (used as a poison) and pennyroyal (toxic side effects), which underlines the need for adequate training.
For therapeutic purposes the quality and wholeness of any essential oils used are of paramount importance, irrespective of cost, whereas when used in the flavour and fragrance industries the price, taste and aroma are the most important considerations; for them, standardized essential oils are necessary to ensure repeatability and a consistent quality.
Variation in the quality of an essential oil may be natural or due to human intervention. Wine is a commodity which is expected to have a different taste and character from year to year, although harvested, processed and bottled at the same vineyard and from the same vines. Plants are subject to varying amounts of sunshine, frost, rain, heat or cold each year, and it is these factors, plus the composition of the soil, which are responsible for the variations in quality and composition (and therefore the aroma) of the plant extracts, occurring naturally from year to year.
Traders in essential oils may add cheaper oils or synthetics to the genuine oils, in order to maintain the same standard taste, aroma and price level for successive repeat deliveries to the same customer. The needs of the flavour and food industries are today so great that there are scarcely enough natural products in the world to meet the demand, and even where available some products are just too expensive for their purposes compared with synthetics. The aromatherapist, however, needs above all to acquire the natural physicochemical characteristics, whatever the variation from harvest to harvest.
Essential oils are made up of a vast array of natural chemicals, most of which are found in more than one oil. It is a fairly simple matter for the chemist to remove a desired constituent from a cheap oil and add it to an expensive oil, or to sell a modified ‘pure’ oil to an unsuspecting customer for a high price. Adulteration also takes place when a synthetic isolate is added, especially to one of the costly oils such as rose otto, when synthetic phenyl ethyl alcohol (occurring naturally in rose otto) is used as the adulterant. ‘Nature identical’ products are manufactured in a laboratory and are simply synthetic copies of ingredients found in nature. Alcohol, and occasionally a small amount of vegetable oil, which are both good solvents of essential oils, are used to adulterate, stretch or cut Nature’s gifts, and many descriptive words are used to justify the standardization sometimes necessary in the fragrance and food industries. ‘Certain suppliers with highly developed imagination will even use the term “ennobling” for the disfiguration of an essential oil’ (Arctander 1960). With some oils it is almost standard practice to adulterate, e.g. the use of PEG (polyethylene glycol) to extend lavender essential oil.
Expensive essential oils such as Melissa officinalis [melissa] and Aloysia triphylla [lemon verbena] are often imitated by the perfume industry by using blends of cheaper oils to simulate the aroma; to the perfumer, the aroma is the most important asset of an ‘essential oil’, not whether it is natural, adulterated or synthetic. Tisserand and Balacs (1995 p. 177) say that Aloysia triphylla should not be used in therapy, but this advice is based on tests carried out at 12% using fragrance quality oils (Opdyke 1992). Most oils named lemon verbena are blends of lemon, citronella, lemongrass etc., as the genuine oil is expensive; these ‘made up’ verbena oils are likely to be phototoxic and also skin sensitizers because of the high citral content in the oils from which they have been constructed. However, the genuine oil, which has a similar concentration of citral to the above oils, does not irritate the skin (Schnaubelt 1998 p.117) – a good reason for not using industrial quality essential oils therapeutically!
Essential oils used in the fragrance industry often have their terpenes partly or wholly removed on account of their insolubility in alcohol, which would result in cloudiness – a distinct commercial and aesthetic disadvantage in a perfume! The deterpenized oil is incomplete and contains in higher proportions the remaining constituents of the oil, for example the deterpenization of peppermint increases the content of the possibly hazardous ketone menthone. In aromatherapy there is no necessity for this and it is imperative not to interfere with the natural balance of the essential oil. Some therapists purchase bergapten-free bergamot oil, as this constituent (a furanocoumarin) can be responsible for phototoxicity of the skin in sunlight, but this is unnecessary (see Ch. 3 Part II).
The majority of essential oils are produced for use by the food and fragrance industries which, generally speaking, are not concerned whether or not fertilizers, pesticides or herbicides may be present in the oil. Stewart (2004 p.10) says that herbicides, fungicides and pesticides are intrinsically toxic and inevitably end up as contaminants in the oils, directly affecting their efficacy and safety.
The various types of aromatic product available are shown in Figure 3.1. For therapeutic use aromatherapists use only distilled essential oils and expressed essences, although some occasionally make exception to the rule by using jasmine absolute or benzoin.
Of the many factors involved in the safe use of therapeutic essential oils, not least is the specification of the oil itself. Knowledge of factors such as where it is grown, whether it is cloned by cuttings or grown from seed, the plant variety, how it is grown (wild, organic, or with chemicals), the part of the plant used and the chemotype is important for safe usage.
A patient being treated for a fistula of the anus by the instillation of pure and natural drops of lavender and who was beginning to recover, had to go on a journey. Having forgotten his essential oil, he purchased a further supply from a chemist. Unfortunately, this essence was neither pure nor natural; one single instillation resulted in such severe inflammation that the patient was unable to sit down for over two weeks.
The overriding consideration must be consumer safety and to this end genuine, authentic essential oils must be procured, genuine in this case meaning of known plant origin and authentic meaning not standardized: note that the word natural does not necessarily mean unadulterated or safe.
4. The trade has very limited knowledge of scientific names and it is vital for aromatherapy to use the scientific name, because the use of local common names for the plants leads to confusion. More than one name may be given to the same plant, or the same common name can be given to different plants (such as marjoram, which might be Origanum majorana or Thymus mastichina).
Cedarwood oil may be any of the following, since all are traded simply as cedarwood: Cedrus atlantica [Atlas cedarwood], Cedrus deodora [deodar or Himalayan cedarwood], Cedrus libani [cedar of Lebanon], Chamaecyparis lawsoniana [western white cedar], Cryptomeria japonica [Japanese cedar], Juniperus procera [east African cedarwood], Juniperus mexicana [Texas cedarwood], Juniperus virginiana [red cedarwood], Thuja occidentalis [white cedar], Thuja plicata [western red cedar].
6. Wild plants are sometimes collected by an unsupervised, unskilled labour force paid by weight of plant collected, and who are not always able to identify the required plant, resulting in indiscriminate harvesting.
The importance of knowing what material is being used in a treatment is obvious, therefore it is imperative that the oil is precisely identified. This fact escapes the attention of many people treating others, and even of some carrying out scientific trials. Before embarking on a trial using essential oils it is of primary importance that a specified oil from a known source is used, and to have as a minimum a GC (gas chromatography) analysis of the oil actually used in the test. The scientific botanical name of the plant should be used and oil from the same harvest batch should be used throughout the test(s).
In many cases it is not sufficient merely to specify the genus and species (and the variety if applicable): it is also necessary to designate the chemotype (explained in Ch. 1) and the part of the plant used for extraction. An example is the cinnamon tree, where the oil from the bark consists principally of an aldehyde, whereas the oil from the leaf is mainly a phenol, with different effects and uses. The oil from the thuja or white cedar tree, Thuja occidentalis (responsible for the restriction on cedarwood oils in France), is taken from the leaves, but other ‘cedarwoods’ are taken from the wood. In the Apiaceae family, the seed oils can be significantly different from oils extracted from other parts of the same plant, e.g. in the case of Angelica archangelica the root oil is phototoxic, whereas that from the seed is not. Therapists need to be aware of this; it is their responsibility to ensure that inappropriate treatment is not given.
• Tea tree – there is three times more sold in the world than is produced in Australia; tea tree oil is a comparatively simple essential oil comprising only about 30 compounds (cf. ylang ylang, with about 1200) and so is easy to reconstruct; also the ‘natural’ oil is often ‘regulated’ at source.
About 60 different standards exist for the chemical composition of essential oils, yet there are only 16 essential oils listed in the New European Pharmacopoeia (Dürbeck 2003). Current pharmaceutical formulae demonstrate that essential oils and oleoresins derived from spices and herbs are valued not only as flavouring agents but also for other properties they possess; for instance, they:
As flavouring agents, essential oils are acceptable for repeated dosage, e.g. in tablets to be chewed and for repeated usage in such products as toothpaste. As perfumes they are present in a variety of cosmetics which are used daily over long periods of time.
Some essential oils listed in the British Pharmacopoeia (BP) are stocked in hospital pharmacies, but oils prepared to BP standards may not be suitable for use in aromatherapy. One reason for this is that many plants, for example thyme, Thymus vulgaris, exist in the wild as many different chemotypes, each chemotype producing quite a different essential oil in makeup and therapeutic action (see Ch. 1 p. 8) and such differences are not always reflected in the pharmacopoeia. Another reason is because the specification is either too broad or incomplete and does not reflect the natural materials currently available; some oils listed are folded, which alters their composition: such essences are not used in aromatherapy.
• Air – oxidation can be a problem and essential oils keep best when bottles are full, with as little air as possible. Oxidation – the combining of free oxygen with compounds in the essential oils – affects some oils particularly, altering their therapeutic effects, e.g.