Evidence-based practice is vital to the provision of safe, effective clinical care.
Although some areas of conventional healthcare remain unevaluated, the culture of defensive practice to avoid litigation is so strong within obstetrics that it is essential to be able to argue the case for the efficacy and safety of aromatherapy in midwifery practice. Aromatherapists, too, who may have contact with midwives or obstetricians, need to be able to support their practice with research findings, in order to justify their actions.
Initially, the majority of essential oil research was undertaken mainly by the cosmetics and food industries, which explored the flavours and aromas, as well as the preservative qualities of the oils. More recently, considerable laboratory research has been conducted on the chemistry and clinical properties of individual oils – for example, the antibacterial effects of oils such as tea tree, one of the most commonly researched essential oils (Mertas
et al. 2015; Warnke et al. 2013). Other research focuses on how aromatherapy works: is it due to the chemical constituents, the method of administration, particularly massage, or the therapeutic relationship between client and therapist?
Investigating single essential oils is acceptable to the medical and pharmaceutical professions, which view chemicals in isolation rather than as a part of the whole therapeutic event. Pharmaceutical companies spend many years and an enormous amount of money on clinical research and the development of new drugs. Since the thalidomide disaster of the 1960s, they are required to demonstrate beyond reasonable doubt that their products are safe for the public, and there are occasions when the potential side-effects on humans are found to be so unacceptable as to warrant discontinuation of the drug’s development. The costs of this system, if applied to aromatherapy and herbal medicine, would be prohibitive, a fact which has been partly resolved through the 2011 EU laws on herbal medicines, which require registration of traditional remedies that have been in use for more than 30 years. Also, since it is not possible to patent natural products, there is no incentive for individual companies to undertake the research with all its accompanying costs, unless they can isolate the single active ingredient, synthesise it and then reproduce it and apply for a product patent. To a certain extent, this has some value in that essential oils and other herbal substances may be the precursors to some new drugs (Abd Kadir, Yaakob and Zulkifli 2013;
Boukhatem et al. 2013), but adhering to the pharmaceutical approach does little to demonstrate the effectiveness and safety of aromatherapy as a clinical modality in its own right.
One of the problems for aromatherapy, as for other complementary therapies, is to demonstrate not only whether the essential oils are effective, but also how they work and whether they are safe, especially in pregnancy.
The biomedical sciences have long seen randomised, double-blinded, controlled trials as the ‘gold standard’ by which all clinical studies should be measured. However, many complementary therapies cannot be investigated in this way because their effectiveness is based on factors that cannot be double-blinded, or treatment selections which must be individualised to each patient. In respect of aromatherapy, subjects could be randomly allocated to receive either an aromatherapy oil/treatment or a placebo/normal care, but studies cannot be double-blinded unless synthetically produced aromas are used in the control group, which in themselves may have some effect. Where massage is used as the method of administration, both the professional and the subject will, of course, be aware of the treatment, in which case a third subject group who receive essential oils via some other route, such as inhalation, will be necessary. There again, we have seen from the discussion in this chapter that there are physiological differences in the absorption of
essential oils between dermal or respiratory administration, adding another complexity to the mix.
Many clinical applications of aromatherapy depend on a composite blend of different essential oils, usually administered via the skin in a massage or some other form of administration. In clinical practice, the aromatherapy treatment should be individualised for each client, and one blend of essential oils would not necessarily be appropriate for other individuals with the same symptoms or condition. There is now a trend in contemporary complementary medical research to study the effectiveness of the ‘package’ of care (i.e. treatment with aromatherapy) rather than its individual components – but this is contrary to the notion of randomised controlled trials, in which single specific aspects are investigated in order to eliminate confounding variables.
Whilst these problems also relate to many other complementary therapies, there are some issues which are pertinent to aromatherapy specifically. The chemistry of individual essential oils is influenced by factors such as geography, climate, the seasons, etc., so it is difficult to draw comparisons between studies which apparently use the same essential oils.
For example, a study using ‘lavender’ could involve the use of high-altitude Alpine lavender or English lavender, which would have different proportions of the same chemical constituents, thus potentially affecting the results.
In addition, there are several different types of some oils, so studies which apparently investigate ‘chamomile’ may, in fact, be using different oils with different chemical compositions – in this case, Matricaria chamomilla (German) or Chamaemelum nobile (Roman). Furthermore, the concept of psycho-aromatherapy adds another dimension to the picture: it is virtually impossible to eliminate the effects of aromas on the limbic centre of the brain when conducting trials of clinical aromatherapy.
Researching aromatherapy in a clinical setting is therefore complicated.
There has, until recently, been little research on the use of aromatherapy in pregnancy and childbirth. What little clinical evidence there is tends to be based on the premise that the essential oils used are generally considered safe enough to use in pregnancy because there is no documented evidence to the contrary. Trials on the potential teratogenic or abortifacient effects of essential oils have been carried out only on animals such as mice, since it would be impossible to obtain ethical clearance to study these effects on pregnant women. However, it is difficult to relate animal physiology to human physiology, so the results can only act as a guide, particularly when the doses used in animal research are often many multiples of what would be considered suitable for clinical aromatherapy practice. Also, whilst humans generally have only one baby at a time, it is normal in animals to produce several offspring – a fact which may cause essential oils to have
variable effects within and between litters. In some species, notably rodents, spontaneous fetal malformations are not uncommon, making it difficult to apportion blame when essential oils are administered. In addition, research animals are kept in a laboratory environment which is unnatural and it is not possible to determine whether the associated stress could have an additional impact on the development of embryonic and fetal malformations.
However, since it is impossible to conduct stringent testing for the safety of essential oils in human pregnancy, it is necessary to place some degree of reliance on animal testing. This means that, where a study has shown adverse effects in pregnant animals exposed to specific essential oils, it would be professionally expedient to avoid using this oil in pregnant humans. For example, Lis-Balchin, a chemist with an interest in essential oils, conducted research on rodents to examine safety in pregnancy. One of the essential oils, tea tree, was found potentially to relax smooth muscle, causing the researcher to comment in her final report that it would be unwise to use tea tree during (human) labour as it could theoretically have an adverse effect on the myometrium (Lis-Balchin 1999). In the absence of any more recent contradictory evidence, this then provides a guide to one essential oil, a fact that could be used by expert witnesses in the event of a case for alleged negligence during a labour in which tea tree had been used being brought to court for compensation.
The method of administration can also become a significant variable in aromatherapy studies. Massage in itself can be an effective therapeutic intervention. When combined with essential oils, the desired outcome may be enhanced, particularly in terms of relaxation, aiding sleep or easing pain. In order to conduct an aromatherapy study using robust research methodology, it would probably be necessary to have subjects randomly allocated to several groups: a control group, an essential oil group using inhalation as the method of administration, a massage group and a group in which both massage and the essential oils are used. For example, several studies have found inhalation of lavender to be effective as a sedative in those with sleep disturbances (Karadag et al. 2015; Keshavarz Afshar et al. 2015; Lillehei and Halcon 2014), whereas Hajibagheri, Babaii and Adib-Hajbaghery (2014) used rose oil in a massage treatment to aid sleep. Not only were different oils and administration methods used in these studies, but the clinical conditions also varied. Interestingly, Hwang and Shin’s (2015) meta-analysis of several studies found that those involving inhalation of an essential oil were statistically more effective in inducing sleep than those which involved an aromatherapy massage treatment. It is therefore very difficult to determine with any degree of certainty whether or not ‘aromatherapy’ – or a specific essential oil – is useful in helping people get to sleep.
Obtaining evidence of the safety of aromatherapy is even more difficult, especially in pregnancy. Most of the information available about safety (or otherwise) of essential oils is based on reporting of adverse effects, although it can be difficult to confirm the validity of these reports, not least because other factors may play a part in producing an apparent adverse effect, whereas many true (direct) adverse reactions may go unreported. On the other hand, there are sufficient reports of the effects of some specific essential oils on humans to provide useful information and to warrant caution. Where these case reports relate to non-pregnant use, it is wise to consider the additional stress on an expectant mother and the fetus and to include the relevant oils in the list of essential oils contraindicated in pregnancy (see Chapter 4).
Caution must also be applied, however, to the nature of the evidence used to demonstrate benefits or hazards of essential oils. There is considerable research evidence on the risks of herbal medicines, but these cannot automatically be applied solely to essential oils, which are only one constituent of herbal remedies. Any proven risks of herbal preparations may be due either to another isolated ingredient or to a combination of chemical constituents which do not occur in essential oils.