3 (Part II) Power and hazards
This term includes irritation, phototoxicity and sensitization. To minimize risk it is important to bear in mind that essential oils must be properly sourced, of the highest quality, botanically identified, well stored and unadulterated (many cases of dermal toxicity can be traced back to substances that have been added for commercial reasons). Steam distilled essential oils are superior to other extracts such as absolutes, concretes, carbon dioxide extracted etc.; lavender absolute was involved in two cases, one a therapist with a 3-year history of dermatitis extending to the face and neck (Bleasel, Tate & Rademaker 2002).
This is a reaction to a substance that produces inflammation and itchiness. Some essential oils are irritating to the skin, and these are usually (but not exclusively) found to contain high proportions of either aldehydes or phenols. Oils in common use which have been found to be irritant are listed in Appendix B.6 (see CD-ROM). Because there appear to be wide variations in tolerance, a given oil might not cause a reaction in the majority of people yet be irritant to one or two more sensitive individuals; dermal irritation produced by essential oils is usually localized and short lived. Assuming that one oil has a 50% presence of an offending component, this is present in the total mix at only 0.5% when the oil is used in a normal massage mix along with two or three other oils at the standard dilution of 3% essential oils in a carrier.
Tagetes – an aromatherapist presented with acute bilateral hand eczema 24 hours after spraying roses with an insecticide and patch testing gave a strong reaction to Tagetes patula [French marigold]; the acute eczema was attributed to a cross-reaction with pyrethroid in the insecticide (Bilsland & Strong 1990). Dermatitis caused by the leaves and flowers of Tagetes minuta, T. patula, T. erecta and T. glandulifera is common in South Africa, and the essential oil of Tagetes glandulifera is sometimes cited as being a skin irritant, but we have not found this to be the case in practice, although it is a photosensitizer.
Brassica nigra [mustard] and Armoracia rusticana [horseradish] – two oils from the Cruciferaceae family which are not normally recommended for aromatherapy use because both consist almost entirely of allylisothiocyanate. These oils applied neat to the skin will provoke severe burning and blistering, but it has been known for them to be recommended at the extremely low concentration of one drop of essential oil in 500 mL of carrier oil for rheumatism.
Melaleuca alternifolia – there are many cases reported of skin irritancy and dermatitis involving tea tree oil (Bhushan & Beck 1997, Southwell, Freeman & Rubel 1997). It should be borne in mind that tea trees are cultivated, grown from seed, and therefore the composition of the oil when distilled is variable. This oil is then adjusted at source to conform to laid down parameters (especially the 1,8-cineole content) and so may not have the natural synergy that may be expected. Tea tree oil has a relatively simple composition (about 30 compounds). Some oils are synthesized in a laboratory and are known as reconstructed oils (RCO); they are not natural products and may have unwanted side effects. Seven people had been applying commercial tea tree oil undiluted on the skin for conditions such as fungal infections, pimples and skin rashes, and all developed eczematous dermatitis, some with vesiculation; a common allergen was (−)-limonene: the application of diluted oil to the skin caused no reaction (Knight & Hausen 1994), showing that use of the commercial oil undiluted was ill advised. Treatment of chronic atopic dermatitis by application of undiluted Melaleuca alternifolia was unsuccessful and then oral ingestion of the oil mixed with honey was advised, which led to exacerbation of the dermatitis; 1,8-cineole was the allergen (De Groot & Weyland 1992). The reasoning behind this treatment is hard to understand.
Santalum album [sandalwood] – overdose due to daily application for 8 years of sandalwood paste to the forehead led to a hyperpigmented, erythematous plaque and lesions and fissures on thumb and forefinger; sandalwood paste patch test proved positive (Sharma, Bajaj & Singh 1987). The offending compound was not identified.
Pimpinella anisum [aniseed], Syzygium aromaticum flos, fol., caul. [clove, bud, leaf and stem] can irritate the skin if used in high concentration because of their phenolic ether and phenol content, respectively.
Cinnamomum verum cort., fol. [cinnamon bark and leaf] – the bark oil contains cinnamal, which is a known skin sensitizer, but the whole oil proves to be less so. A patch test should always be carried out prior to using this oil.
Of 1500 dermatitis patients who were patch tested, 21 had a reaction to essential oils (which were not botanically specified) of pine needle, dwarf pine, clove and eucalyptus, and it was found that some components of the essential oils – carene, phellandrene and eugenol – were sensitizers (Woeber & Krombach 1969). The regional provenance of the essential oils had no great influence on sensitization potency: good quality and lack of ageing were more important. A therapist with a 3-year history of forearm dermatitis was sensitive to a range of oils containing geraniol but was also sensitive to yarrow, laurel and peppermint oils, which do not contain geraniol (Bleasel, Tate & Rademaker 2002).
More than 95% of users of essential oils in aromatherapy are women, hugely outnumbering men: perhaps it is relevant that a Japanese study showed that the skin of men tends to be more than twice as sensitive as that of women, and that in situations of severe stress, lack of sleep, etc. all skins are rendered more sensitive (Hosokawa & Ogwana 1979).
Generally speaking, essential oils with a substantial content of phenols (chiefly thymol, carvacrol and eugenol) can be responsible for irritating a mucous membrane. Oils containing aldehydes may also be implicated. In the past it was believed that the hydrocarbon terpenes caused mucous membrane irritation (Gattefossé 1937 p. 40) but this is now thought not to be the case. Any of the oils listed in Appendix B.6 (see CD-ROM) may cause irritation of the mucous membranes of the alimentary, respiratory and genitourinary tracts. A possible exception is lemon oil, which contains less than 5% aldehyde and consists mainly of hydrocarbon terpenes, principally (+)-limonene, which is known to quench the irritant effect of the aldehyde.
There are some oils that do not produce any reaction on first contact with the skin but may do so on a subsequent application; there seems to be no common denominator to those essential oils that are sensitizing. The body’s reaction involves the immune system, via the cells in the basal layer of the epidermis. Poor storage of oils containing a significant amount of monoterpenes can lead to the formation of sensitizing hydroperoxides: an infamous example is turpentine, which is responsible for skin allergies in workers in the paint industry. Oils to be wary of in this respect are shown in Appendix B.8 (see CD-ROM).
Once a person is sensitized to one substance, that person is more likely to be susceptible to other similar substances, although the risk is low. This need not cause concern, but any aromatherapist who is sensitive to substances should be aware of the possibility. This is a complex topic, not well understood, but one example is that people can become sensitive to benzoin after sensitization to Peru balsam or turpentine. There is a similar relationship between turpentine and peppermint, and a case of turpentine-induced sensitivity to peppermint oil involved a laboratory technician who suffered swelling of tongue, lips and gums after a dental operation. Tests revealed sensitivity to peppermint oil, an ingredient in dental spray and mouthwash, and this was due to α-pinene, limonene and phellandrene, which are also present in turpentine, from which he had previously developed severe eczema of the hands (Dooms-Goossens et al. 1977): Cymbopogon martinii [palmarosa] is implicated in cross-sensitization with lavender, lemongrass and geranium.
An aromatherapist had a 12-month history of hand and forearm dermatitis which improved when away from work. Patch testing revealed positive reactions not only to oils of lavender, geranium and lemongrass, but also to oils to which she had not been previously exposed (palmarosa, frankincense, rose, neroli, myrrh), which implied cross-reactivity (Bleasel, Tate & Rademaker 2002). Dermatitis recurred after eating lemongrass- flavoured food – systemic contact dermatitis.
A man allergic to turpentine breathed in the vapour of tea tree oil in hot water to help his bronchitis and developed acute exudative dermatitis of the face, trunk and arms (De Groot 1996). The origin of the essential oil was not stated. A woman who had been treating her acne for a long time with undiluted Melaleuca alternifolia [tea tree] essential oil without reaction presented with dermatitis on her forehead and mouth: patch testing was positive to tea tree and colophony (an oleo resin from which turpentine is distilled): crossreaction between turpentine and colophony had already been established (Selvaag, Erikson & Thune 1994). Palmarosa has been implicated in cross sensitization with lavender, lemongrass and geranium (Dooms-Goossens et al. 1977 p. 73), and galbanum resin has been linked in cross-sensitization with Peru balsam (see also Appendix B on the CD-ROM).
Photosensitization is a process in which reactions to normally ineffective radiation are induced in a system by the introduction of a radiation-absorbing substance – the photosensitizer (Kochevar 1987). Photosensitivity may occur when certain essential oil components, particularly the expressed essences, react with the skin under the influence of ultraviolet rays, yet does not occur on skin protected from natural or artificial sunlight. It may result in erythema, hyperpigmentation and perhaps vesicles, depending on the severity of the reaction. Furanocoumarins (psoralens) appear to be primarily responsible for phytophototoxic reactions in humans (Lovell 1993), so care needs to be taken with the citrus essences, which are expressed from the peel and contain furanocoumarin molecules, particularly bergamot. Other oils exhibiting this characteristic at aromatherapeutic doses are Angelica archangelica rad. [angelica root], Juniperus virginiana [Virginian cedarwood], Ruta graveolens [rue], Lippia citriodora [lemon verbena] and Cuminum cyminum [cumin] (Opdyke 1974) (see Appendix B.7 on the CD-ROM).
Factors that influence the phototoxic response to psoralens are the presence of a suntan, natural pigmentation (dark skin), site of application, skin hydration, and the interval between application of the psoralen and irradiation (it is worth mentioning that aromatherapy oils are applied mainly to areas not normally exposed to sunlight). A particularly notable culprit is the expressed oil of Citrus bergamia [bergamot] (Opdyke 1973), which was studied by Zaynoun, Johnson and Frain-Bell (1977), and its use in aromatherapy needs consideration; tests by Pathak and Fitzpatrick (1959) have shown the time interval between applying psoralens and the maximal phototoxic effect to be 30–45 minutes (tested on guinea pig and human skin), and a later test (Arora and Willis 1976) indicated a time interval of up to 75 minutes.
Tests probably carried out for the benefit of the perfumery trade on bergamot oil in ethyl alcohol showed no phototoxic responses at a concentration of 0.5%, and at 1.0% no phototoxic response after 8 hours; the tests were carried out on five subjects (Zaynoun, Johnson & Frain-Bell 1977 p. 231) and also showed that intervals of 1–2 hours between application and irradiation yielded a maximal phototoxic response. Applying this directly to aromatherapy is questionable, as aromatherapists do not use ethyl alcohol as a medium for application, and the flow of psoralen through the horny layer of the skin is dependent on the carrier used (Kaidbey & Kligman 1974, Kammerau et al. 1976). It is known that the horny layer is a major barrier to the penetration of psoralens; in tests, 70–90% of topically applied 8-methoxypsoralen (8-MOP, xanthotoxin, which is not present in bergamot oil) did not enter the horny layer and was finally lost through sloughing (Kammerau et al. 1976). Bergamot oil itself is resorbed through the skin in 40–60 minutes (Römelt et al. 1974, Valette 1945).
The tests by Zaynoun, Johnson and Frain-Bell (1977 p. 232) also showed that using paraffin molle flavum (PMF) as the carrier resulted in increased speed of penetration through the horny layer and produced a shorter period in which phototoxicity persists than when using ethanol, and it is possible that the effects using a vegetable oil as a carrier more closely resemble the results using PMF than those using alcohol.
The IFRA Committee recommends a level of 5-MOP (bergapten, a naturally occurring analogue of psoralen) of 75 ppm in a (fragrance) compound, and assuming a 5-MOP content of 0.35% this equates to a level of expressed bergamot oil in the compound of 2% (Jouhar 1991), which translates to 0.4% (about eight drops in 100 mL) in an aromatherapy preparation applied to skin. The use of 5-MOP is forbidden in the EU except as a normal component of essential oils.
In practical experience over four decades, there has been no reported problem by thousands of therapists who have followed our training and numerous clients who have followed our advice. On this basis, it is suggested that following the application of bergamot oil using the normal aromatherapy dilution (usually less than 1% in synergistic blends) it is reasonably safe to expose the skin of normal people to sunlight provided that more than 2 hours have elapsed since the application. This advice may be tempered in case of any unusual sensitivity in the individual client. It is interesting to note that some other simple coumarin derivatives, such as umbelliferone, herniarin and aesculetin, have a sunlight filter effect because they absorb ultraviolet light of 280–315 nm (Schilcher 1985 p. 228).
It is necessary to be wary of reported cases now that the fragrance industry relies so heavily on synthetic materials. An example is a middle-aged man who used a sandalwood aftershave lotion for 3 weeks which brought about weeping, lichenified dermatitis of the face which worsened in sunlight, even after discontinuing the aftershave lotion. On analysis the commercial sandalwood was found to be composed of synthetic and natural geranium, synthetic and natural sandalwood, cedarwood oil and patchouli oil; he tested positive to both synthetic and natural geranium.
If any one oil is used for a very long period there may be a risk of sensitization even though none exists in normal usage. When eau de Cologne (which contains bergamot and other citrus essences) was much in vogue many people wore it daily over a period of years and developed raised erythematous rough skin where the eau de Cologne had been applied – usually on the neck (berloque dermatitis). This reaction can be semi-permanent, lasting for years after fragrance use has ceased before disappearing (Shirley Price’s personal experience). Many perfumes have ingredients in common with eau de Cologne and may produce similar reactions. A 47-year-old woman who sold food that was smoked and spiced with juniper berry oil, had for 25 years had a rash that had become generalized, followed by a dry cough and asthma; skin tests with juniper and pine oils proved positive (Rothe, Heine & Rebohle 1973).
Melaleuca alternifolia [tea tree] oil was identified as a possible cause of relapsing eczema in a 53-year-old woman who had prolonged exposure to the oil (Schaller & Korting 1995). She was also allergic to other essential oils, including lavender, jasmine and rosewood, which may also have resulted from prolonged exposure to the oils, but she was in addition allergic to laurel and eucalyptus, to which she had not been previously exposed. This report emphasizes the importance of treating essential oils with respect, especially when using them for prolonged periods. It is good aromatherapy practice to change the oils used during a treatment of long duration.
A survey carried out (Wong 1995) on the personal effects on 120 aromatherapists using essential oils in treatments revealed that they occurred on many levels. A few therapists suffered adverse effects, but it was felt that these were due to reactions to clients rather than to the oils themselves. It is emphasized that this was a survey, not a properly constituted trial. Of the 120 therapists surveyed:
• Most experienced positive effects such as an improvement in PMS, period pains and menopausal symptoms, and a more regular menstrual cycle. Salvia sclarea [clary sage] was mentioned many times in this context.
• A few therapists felt adverse effects such as tender breasts, irregular or heavy menstruation, a change in menstrual cycle and fluctuating hormone levels, but these are common and may not be linked to essential oil use.