MD, PhD, FMedSci, FSB, FRCP, FRCPEd

My aim with this blog is to eventually cover most of the 400 or so different alternative therapies and diagnostic techniques. So far, I have focused on some of the most popular modalities; and this means, I have neglected many others. Today, it is time, I think, to discuss aromatherapy, after all, it is one of the most popular forms of alternative medicine in the UK.

Aromatherapists use essential oils, and this is where the confusion starts. They are called “essential” not because humans cannot do without them, like essential nutrients, for instance; they are called “essential” because they are made of flower ESSENCES. The man who ‘discovered’ aromatherapy was a chemist who accidentally had burnt his hand and put some lavender essence on the burn. It healed very quickly, and he thus concluded that essential oils can be useful therapeutics.

Today’s aromatherapists would rarely use the pure essential oil; they dilute it in an inert carrier oil and usually apply it via a very gentle massage to the skin. They believe that specific oils have specific effects for specific conditions. As these oils contain pharmacologically active ingredients, some of these assumptions might even be correct. The question, however, is one of concentration. Do these ingredients reach the target organ in sufficient quantities? Are they absorbed through the skin at all? Does smelling them have a sufficiently large effect to produce the claimed benefit?

The ‘acid test’ for any therapeutic claim is, as always, the clinical trial. As it happens a new paper has just become available. The aim of this randomised study was to determine the effects of inhalation aromatherapy on pregnant women. Essential oils with high linalool and linalyl acetate content were selected and among these the one preferred by the participant was used. Thirteen pregnant women in week 28 of a single pregnancy were randomly assigned into an aromatherapy and a control group. The main outcome measures were several validated scores to assess mood and the heart-rate variability. The results showed significant differences in the Tension-Anxiety score and the Anger-Hostility score after aromatherapy. Heart rate variability changes indicated that the parasympathetic nerve activity increased significantly in the verum group. The authors concluded that aromatherapy inhalation was effective and suggest that more research is warranted.

I have several reasons for mentioning this study here.

1st research into aromatherapy is rare and therefore any new trial of this popular treatment might be important.

2nd aromatherapy is mostly (but not in this study) used in conjunction with a gentle, soothing massage; any outcome of such an intervention is difficult to interpret: we cannot then know whether it was the massage or the oil that produced the observed effect. The present trial is different and might allow conclusions specifically about the effects of the essential oils.

3rd the study displays several classic methodological mistakes which are common in trials of alternative medicine. By exposing them, I hope that they might become less frequent in future.

The most obvious flaw is its tiny sample size. What is an adequate size, people often ask. This question is unfortunately unanswerable. To determine the adequate sample size, it is best to conduct a pilot study or use published data to calculate the required number of patients needed for the specific trial you are planning. Any statistician will be able to help you with this.

The second equally obvious flaw relates to the fact that the results and the conclusions of this study were based on comparing the outcome measures before with those after the interventions within one intervention group. The main reason for taking the trouble of running a control group in a clinical trial is that the findings from the experimental group are compared to those of the control group. Only such inter-group comparisons can tell us whether the results were actually caused by the intervention and not by other factors such as the passage of time, a placebo-effect etc.

In the present study, the authors seem to be aware of their mistake and mention that there were no significant differences in outcomes when the two groups were compared. Yet they fail to draw the right conclusion from this fact. It means that their study demonstrated that aromatherapy inhalation had no effect on the outcomes studied.

So, what does the reliable trial evidence on aromatherapy tell us?

A clinical trial in which I was involved failed to show that it improves the mood or quality of life of cancer patients. But one swallow does not make a summer; what do systematic reviews of all available trials indicate?

The first systematic review was probably the one we published in 2000. We then located 12 randomised clinical trials: six of them had no independent replication; six related to the relaxing effects of aromatherapy combined with massage. These 6 studies collectively suggested that aromatherapy massage has a mild but short-lasting anxiolytic effect. These effects of aromatherapy are probably not strong enough for it to be considered for the treatment of anxiety. We concluded that the hypothesis that it is effective for any other indication is not supported by the findings of rigorous clinical trials.

Since then several other systematic reviews have emerged. We therefore decided to summarise their findings in an overview of all available reviews. We searched 12 electronic databases and our departmental files without restrictions of time or language. The methodological quality of all systematic reviews was evaluated independently by two authors. Of 201 potentially relevant publications, 10 met our inclusion criteria. Most of the systematic reviews were of poor methodological quality. The clinical subject areas were hypertension, depression, anxiety, pain relief, and dementia. For none of the conditions was the evidence convincing. Our conclusions therefore had to be cautious: due to a number of caveats, the evidence is not sufficiently convincing that aromatherapy is an effective therapy for any condition.

Finally, we also investigated the safety of aromatherapy by assessing all published data regarding adverse effects. Forty two primary reports met our inclusion criteria. In total, 71 patients had experienced adverse effects after aromatherapy which ranged from mild to severe and included one fatality. The most common adverse effect was dermatitis. Lavender, peppermint, tea tree oil and ylang-ylang were the most common essential oils responsible for adverse effects. We concluded that aromatherapy has the potential to cause adverse effects some of which are serious. Their frequency remains unknown.

And what is the conclusion of all this? To me, it seems fairly straight forward: Aromatherapy is not demonstrably effective for any condition. It also is not entirely free of risks. Its risk/benefit profile is thus not positive which can only mean that it is not a useful or recommendable treatment for anybody who is ill.

6 Responses to Aromatherapy

  • I understand from the findings of cognitive neuroscience that aroma frequently plays a significant role in forming both short- and long-term memories.

    One thing that doesn’t need double-blind RCTs to establish is that the majority of people are more tempted to buy a house that had an aroma of coffee and freshly-baked bread than one that had an aroma of damp and mildew (mushroom fanatics may disagree with me on this point!).

    A trial of aromatherapy, as in using aromas plus massage, obviously cannot delineate between the separate effects. Trials of aromas are very interesting, but they cannot answer my question “Did this massage therapist use aromas as a sales tactic or was he/she an aroma ‘expert’ using massage as a sales tactic?”

    Some may think I’m being cynical instead of skeptical: to those I ask “Why do I never see and smell lovely flowers on my GP’s desk and why does he/she never offer me a massage to make me feel much better about my illness?” Surely, if the benefits outweigh the risks then this therapy must be incorporated into primary healthcare ASAP: patients gain and the NHS saves money. I don’t subscribe to conspiracy theories therefore I remain skeptical of aromatherapy as a low risk efficacious treatment for any condition.

    Those most at risk from the sometimes harmful effects of aromatherapy are the full-time therapists. I sincerely hope that the UK Health & Safety Executive is being properly informed when the adverse reactions occur.

  • I admire the detailed and thorough analysis. It’s enough for me that it’s very often administered in hairdressers and beauty parlours.

  • Using essential oils with a nice smell is not therapy and it is not a treatment. It is wellness. Don’t medicalize useless wellness rituals.

    • Catherine

      It seems that aromatherapists are the ones medicalising aromatherapy. For example this one:

      Some of the conditions aromatherapy is used for include:

      Anxiety, stress or insomnia
      Muscular aches and pains
      Recovering from injuries, convalescing
      Headaches
      Digestive problems
      Menstrual or menopausal problems
      Emotional overloads

      And this one:

      Aromatherapy is particularly good at helping to address the following

      Stress
      Depression
      Insomnia
      ME
      Arthritis
      Skin problems
      Sinusitis
      Muscular aches and pains
      Many more conditions, too many to list here

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