Eucalyptus oils are being used with increasing frequency in a variety of products found in the supermarket or pharmacy. ‘With extract of Eucalyptus’ or ‘With Eucalyptus essential oil’ claims are becoming more common on the labels of modern consumer products such as cosmetics, toiletries and household products due to the ever-increasing interest in natural or botanical ingredients. Eucalyptus oil may be used as an active ingredient to provide scientifically provable benefits – such as nasal decongestion or antibacterial effects – or at much lower dosages to impart more esoteric or folkloric connotations to the product concerned. Eucalyptus oils are also used as components of perfumes to provide a medicinal-type note to the fragrance.
Eucalyptus globulus, or Blue Gum, oil was a traditional Australian aboriginal remedy for infections and fevers. It is now used all over the world for relieving coughs and colds, sore throats and other infections. Its main constituent, 1,8-cineole, is mucolytic (i.e. it thins out and relaxes the flow of mucus) and is excreted through the lung surface. Eucalyptus radiata oil is sometimes preferred by aromatherapists for its more pleasant smell while Eucalyptus smithii oil is sometimes preferred due to a perception that it is better tolerated by the skin. Eucalyptus radiata and Eucalyptus smithii oils have also been shown to be useful for treating disorders of the respiratory system, although with some differences in their uses. A steam inhalation with Eucalyptus is not only an effective cold treatment because it relieves nasal and bronchial congestion, but because it is also claimed to inhibit proliferation of the cold virus ().
When applied as a diluted oil on the skin Eucalyptus has a warming and slightly anaesthetic effect. Massaging with such an oil, therefore, will help to relieve respiratory infections, pain caused by rheumatic joints, neuralgia, fibrositis and muscular aches. Burns, blisters, insect bites and skin infections such as abscesses are also claimed to respond positively to the topical application of the essential oil or extract. It is also said to be valuable for easing the symptoms of shingles, chickenpox and cold sores.
Another common name for eucalyptus is Fever Tree. Baron Ferdinand von Müller, the German botanist and explorer who was Director of the Botanical Gardens in Melbourne from 1857 to 1873, is credited with making the properties of eucalyptus known outside Australia. Due to the medicinal smell of the leaves, nineteenth century colonists planted the trees in fever-ridden areas in various parts of the world in an attempt to drive away insects and contagious diseases. Since the high water-holding capacity of the trees’ root systems coincidentally tended to dry out marshy soils, disease-carrying insects such as mosquitoes, which need standing water to breed, were effectively deterred.
Topically applied oils from certain eucalypts also repel mosquitoes from the skin. A preparation from Eucalyptus citriodora, Lemon-scented Gum, has been used in China for many years under the name Quwenling. In Europe, a formulation based on Quwenling is now being used in ‘natural’ insect repellent products such as Mosi-guard Natural, marketed by MASTA in the UK.
- 1 The use of eucalyptus oils in perfumery
- 2 Eucalyptus citriodora and other oils
- 3 The use of eucalyptus oils in consumer products
- 4 Legislation in Europe and the United States
The use of eucalyptus oils in perfumery
Although more generally associated with medicinal usage, Eucalyptus globulus oil is the most common eucalyptus oil used in perfumery. It consists mainly (approximately 70—75 per cent) of 1,8-cineole (sometimes referred to as eucalyptol and, occasionally, as cajeputol). Cineole has a molecular weight of 154 and boils at 176°C. The remainder of the oil consists of a complex mixture of monoterpenes, sesquiterpenes, sesquiterpenols, aliphatic alcohols, monoterpenones and aldehydes ().
Apart from contributing to the fragrance, 1,8-cineole has two important pharmacological properties: it stimulates the mucous-secreting cells in the nose, throat and lungs and it has an antiseptic effect. Eucalyptus globulus oil is a low-cost essential oil which is comparatively stable in soap (and has long been known for its antiseptic properties, e.g. Martindale 1910) and Poucher (1991) reports an effective antiseptic natural soap perfume. It consists of:
It is often the case that small amounts of Eucalyptus are used to claim aromatherapy effects, even though the contribution to the overall fragrance theme is minimal. However, in a floral fragrance for soap the inclusion of only 0.5 per cent of Eucalyptus can have a lifting effect on the fragrance.
Eucalyptus oil is used in many Australian products, such as fabric softeners and shampoos, in order to support a product-marketing theme. Australian wool wash detergents also often include eucalyptus oil because of its renowned stain-removing properties. However, in most countries an overt eucalyptus note would not be acceptable.
1,8-Cineole is stable in hypochlorite bleach and actually stabilises the chlorine loss. Eucalyptus oil, or cineole itself, is therefore often used in fragrances designed to be incorporated in bleach products at levels between 5 and 35 per cent.
Thus, it can be seen that eucalyptus oil, and its constituent 1,8-cineole, have a valuable place in the perfumer’s palette because of the powerful message delivered by such a characteristic odour.
As an alternative to using the oil itself, a solvent extract (termed an ‘absolute’) can be produced from the leaves and branches of Eucalyptus globulus. This is usually solid at room temperature and has an aromatic-fruity note rather than the typical eucalyptus odour. It has found use in alcoholic fragrances but is more expensive to produce than the oil and is not so widely used.
Eucalyptus citriodora and other oils
Eucalyptus citriodora oil, like citronella oil, has a lemon-like odour and contains citronellal as the principal constituent. However, when a ‘clean’ citrus effect is required, one that can be seen as very functional smelling, then Eucalyptus citriodora oil is the product of choice. Hence its use in laundry soaps and powders; it is especially popular in Africa for this purpose. It is also used in other low-cost soaps, perfumes, air fresheners and disinfectants.
E. staigeriana oil from Brazil also has a lemon-like character – this time due to the presence of citral – and although it is used in perfumery its limited availability and rather higher price means that it is not used on anything like the scale of Eucalyptus citriodora oil.
The safety of eucalyptus oils in fragrances
Although the fragrance industry is covered by normal consumer protection laws, it has also established a self-regulatory mechanism to ensure that the ingredients used in fragrances do not pose a risk to the consumer. This self-regulatory system involves the close cooperation of two major international fragrance organisations: the Research Institute for Fragrance Materials (RIFM) and the International Fragrance Association (IFRA).
Research Institute for Fragrance Materials
RIFM was established in 1966 by the American Fragrance Manufacturing Association as a nonprofit making, independent body whose task is to check the safety of fragrance ingredients. To date, RIFM has tested over 1300 fragrance materials, including all of the commonly used ingredients. The test results for each material examined are reviewed by an independent international panel of toxicologists, pharmacologists and dermatologists and the results are published as monographs in the journal Food and Chemical Toxicology. RIFM also collates all the information available for an ingredient from the scientific literature and from the aroma chemical manufacturers for inclusion in these monographs. Should there be any cause for concern about the use of an ingredient this is immediately signalled to the industry by RIFM through the publication of an advisory letter, which is then acted upon by IFRA.
The type of basic tests carried out by RIFM include acute oral toxicity; acute dermal toxicity if the oral toxicity is significant; skin irritation and sensitisation; and phototoxicity if the material absorbs in the UV range. Where there is a need, more detailed studies are undertaken involving sub-chronic feeding, dermal absorption and metabolic fate. Through IFRA, RIFM also collects from the industry consumer exposure data on fragrance ingredients. This ensures that the test data it has are relevant to the market situation and also provides guidance on the requirements for future research. Thus, RIFM will undertake a review of its safety data, or instigate further research, if the results of these surveys indicate that a particular ingredient is occurring in a wider range of products and/or at higher concentrations than was the case when it was first examined.
International Fragrance Association
IFRA was established in 1973 by trade associations representing over 100 fragrance manufacturers in fifteen countries. It represents the scientific and technical expertise of the industry and is responsible for issuing and up-dating the ‘Code of Practice’ upon which the whole self-regulation policy is based. IFRA is funded by these fragrance manufacturing companies, who all agree to abide by the code of practice whilst they remain members of the association. This code of practice has many functions, including setting standards for good manufacturing practice within the industry, as well as standards for quality control and for labelling and advertising. It also sets limits on, or prohibits the use of, certain ingredients.
Although IFRA and RIFM are independent of each other they work closely together and it is only after considerable discussion between them that restrictions or prohibitions are imposed. It is always the IFRA board in conjunction with the technical advisory committee who make the final decision in such matters, as they are ultimately responsible for the implementation of any restrictions, by way of the code of practice. The most common cause for a use restriction is the ability of some materials to be skin sensitisers. Unlike skin irritation, which usually disappears soon after the irritant has been removed, skin sensitisation involves the activation of the immune system and reactions can persist for much longer after the initial exposure and become more severe on subsequent contact. The strict code of practice applied by IFRA not only protects the consumer but also protects the health and well-being of those employed within the industry.
Eucalyptus globulus and Eucalyptus citriodora oils
Eucalyptus oil of the type from Eucalyptus globulus, and that from Eucalyptus citriodora, have both been the subjects of RIFM monographs (). Opdyke () also gives a separate monograph on eucalyptol. Neither oil has been found to be harmful, irritating or sensitising. Both oils were tested on human volunteers in 48-h closed patch tests at a concentration of 10 per cent in petrolatum and neither was irritating. Eucalyptus globulus oil was also tested undiluted and still gave a negative result. When subjected to a human maximisation test, again at a level of 10 per cent in petrolatum, neither oil was found to be sensitising (). Use of these oils in fragrance compositions is therefore not restricted by IFRA.
Legislation in Europe and the United States
In Europe, Eucalyptus globulus oil has to be labelled for bulk handling purposes under the Dangerous Substances Directive (67/548/EEC) as its flashpoint is 48°C and it is classified as Flammable (R10). It is not classified for either health or environmental effects. Eucalyptus citriodora oil is not classified for health, environmental or physico-chemical (flammability) effects. More detailed information on packaging and labelling requirements for the handling and transportation of eucalyptus oils, particularly those arising from European legislation.
The situation in the United States is slightly different to that in Europe. Drums of either of the two oils are required to be labelled for worker protection with the phrase ‘May irritate skin and eyes’. For transportation purposes Eucalyptus globulus oil is classified as a flammable liquid while, again, Eucalyptus citriodora is not classified.
At the present time, under the sixth Amendment to the European Cosmetics Directive (96/335/EC), if either Eucalyptus globulus or Eucalyptus citriodora oils are used in a cosmetic product they need to be listed as an active ingredient on the label of that product under their Linnaean name.
The European Biocidal Products Directive (98/8/EC) which is being implemented at the present time may also have some labelling consequences for eucalyptus oils. Eucalyptus oil, in particular that from Eucalyptus citriodora, is known to have insect repellent properties and repellents are included in this legislation. The exact consequences for consumer product labelling are as yet unclear, but it would appear that if biocidal properties are claimed for a product then the active ingredient must be named on the label, and listed on the annexes to the directive. However, legal opinion in Europe (Commission DGIII) is of the view that this will not affect cosmetic products since a cosmetic product cannot be a biocidal product at the same time. In this case, neither cosmetic products nor their ingredients will have to comply with any of the requirements of this directive.
The use of these oils is not regulated or restricted in consumer products in the United States.
Selections from the book: “Eucalyptus. The Genus Eucalyptus”. Edited by John J.W. Coppen. Series: “Medicinal and Aromatic Plants — Industrial Profiles”. 2002.