Discussion

Two double blind randomised controlled studies were conducted using validated measurement tools to determine the potential benefit of using aromatherapy products to aid relaxation and promote wellbeing in a young adult student population. The studies took place in Trinity College Dublin in 2021 and 2022, one study using room diffusion and one using an aromastick. A test and control formulation using essential oils was prepared by a clinical aromatherapist for each study. The duration of the interventions was one week and four weeks, respectively. In Study 1 the results showed a statistically significant reduction in the test group intervention in both the stress (p = 0.0291) and depression (p = 0.04) levels of the participants and to a lesser degree in anxiety (p = 0.25) (Fig. 3).  In Study 2, the results were in favour of the test group intervention with the level of wellbeing increasing over the 4-week period achieving statistical significance (p = 0.0058) (Fig. 5). There was no evidence of adverse effects.

Recent studies have shown that the aromatic compounds in specific essential oils can produce an anxiolytic effect [24,25]. The most frequently used essential oils to reduce anxiety are; lavender (Lavandula angustifolia), rose (Rosa damascena)  and the fruit, flowers and leaves from the orange trees (Citrus sinensis and Citrus aurantium L) [12,22,36-41]. The primary pharmacological effect of Lavender (Lavandula angustifolia) essential oil, with its calming and sedative properties, may be attributed to its key components, linalool and linalyl acetate [25]. Similar therapeutic effects have been shown for monoterpene compounds such as limonene, which is the dominant constituent in Citrus aurantium L, Citrus sinensis and Boswellia carterii [42]. Furthermore, these volatile molecules within essential oils have also been investigated for their potential effect on the central nervous system (CNS). Linalool has been shown to act as an inhibitor on the glutamate binding in the CNS to produce anxiolytic effects [24,43-45]. Based on the presence of these specific components, and supported by clinical studies, the essential oils of lavender, orange, neroli and frankincense (Boswellia carterii) were used in the essential oil blend of the current study [42,46,47]. Vetiver (Vetiveria zizanioides) an essential oil noted for its mildly sedative and relaxing properties [48], was the final essential oil added to the blend. It also balanced the aroma and acted as a natural fixative.

There are various validated questionnaires used to measure levels of stress and anxiety using a Likert scale. The Depression, Anxiety & Stress Scale (DASS-42) questionnaire was designed to evaluate levels of depression, anxiety and stress, and was chosen for Study 1 due to its comprehensive range of forty-two questions and the fact that it is a commonly used and validated measurement tool for stress and anxiety in clinical studies [49-51]. Other tools considered were: The Spielberger’s State-Trait Anxiety Scale (STAI); [52,53] and the Hospital Anxiety and Depression Scale (HADS) [54,55]. While psychological measurement tools are largely self-reporting, an increasing number of studies are including physiological measurements including salivary cortisol, vital signs and heart rate variability. Such additional measures strengthen the validity of a study and lead to more convincing evidence  [18,31,47,56,57].

The analysis of Study 1 highlighted the fact that the DASS-42 questions were highly sensitive and might be better employed as indicators of clinical anxiety rather than to gauge the impact of an aromatherapy intervention on levels of relaxation and wellbeing. For example, questions such as: “I felt that life was meaningless” / “I felt that life wasn’t worthwhile” do not seem well aligned to the aim of the study. On that basis, a more appropriate questionnaire was chosen for Study 2. The Warwick, Edinburgh Mental Wellbeing Scale (WEMWBS) has been used in clinical studies and is considered a reliable and valid measurement tool to measure wellbeing and relaxation [33-35].

Despite the low sample size in these pilot studies (17 and 33 participants, respectively), thereby limiting their statistical significance, a notable statistical significance was observed in favour of the aromatherapy test intervention. While feasibility and pilot studies can overestimate positive outcomes, they do provide an opportunity to investigate the potential for the introduction of a new treatment into clinical practice without the costly investment of a larger scale clinical trial [58,59]. A pilot study with a well-designed and methodologically sound approach, even with a limited sample size, can yield compelling results to power subsequent larger-scale studies [47,60,61].

Traditionally, aromatherapy research has been largely anecdotal with poor design and methodology impacting the quality of the results. Clinical studies investigating the impact of aromatherapy have improved in recent times with an increase in double blind clinical trials that employ quantitative measurements to evaluate the patient experience. This was evidenced by a recently published systematic review by the authors of this current study [22].

In the current studies, the formulations for the test and control products were prepared by a clinical aromatherapist. To ensure consistency, the specific plant species of essential oil and a precise dosage was used for both the test and control products. This was supported by source of supply, batch numbers and safety data documentation. No adverse reactions were reported by the participants. The response to aroma is subjective and personal to an individual who may also have expectations to a recognisable aroma such as lavender (Lavandula angustifolia). To minimise such potential bias, the test aroma contained a blend of five essential oils not easily recognisable to the participants. In aromatherapy research, control interventions frequently involve the use of an odourless vegetable oil or the provision of standard care only. Nevertheless, it was considered essential in both studies that the control groups have an aroma to help maintain participant engagement and reduce potential bias. In order to assess the olfactory function for each participant, which was especially important as the study took place during the COVID-19 pandemic, an organoleptic profile was completed by each participant at the beginning of the study. No apparent evidence of anosmia was observed for any of the participants.

Clinical studies have explored the role played by the olfactory response to aroma and the influence that positive odour-associated memories can exert on health and well-being [62,63]. In the first questionnaire and after the initial use of the product, participants were asked if the aroma conjured up any memory for them. The responses from the participants evoked largely positive memory associations, such as, “Reminds me off a wellness centre or spa” / “When I used to use lavender oil on my pillow when I couldn’t sleep” / “Fresh, sunny, carefree walks next to lemon trees in Italy” (Text box).

In Study 1 the test intervention reported statistically significant results in both studies. In Study 1, there was a statistically significant improvement in the test group for depression (p = 0.04) and stress (p = 0.0291) and to a lesser degree for anxiety but a trend was observed in favour of the test intervention (p = 0.25), Fig. 3.

In the first DASS questionnaire which was completed before the intervention, the scores for extremely severe and severe were alarming for depression (12%), anxiety (30%) and stress (35%). The DASS-42 scores were divided into normal, mild, moderate, severe, or extremely severe for each of the three categories: depression, anxiety and stress (see Methods for DASS-42 score chart). However, these scores were reduced in most cases after using the products at the end of the one week of intervention. For participants who completed the second DASS questionnaire, the control group scores for depression, anxiety and stress decreased slightly in both the severe and extremely severe categories. The test group reported a greater reduction across all categories to be within the moderate, mild and normal ranges of depression stress on completion of the one week intervention. Those participants who showed a disimprovement in the test group were within the normal to mild range (see Fig. 2 for changes in individual results).

In Study 2 the control group comprised of 20% of participants with low wellbeing and 80% at moderate wellbeing at the beginning of the study (T=0) as opposed to the test group whose wellbeing was much lower with 61% with low wellbeing and only 39% moderate wellbeing. A delta analysis was conducted to normalise the wellbeing scores at baseline reporting a statistical significance for the test intervention (p = 0.0058) (see Fig. 6b). A paired t-test analysis indicated a statistically significant improvement in wellbeing for the test group (p = 0.002). The mean scores in the completion of the WEMWBS questionnaire reported a significant change in the test group from before (T=0) and after the four-week period (T=4) (41.8 to 51.9) compared with a slight change in the control group (46.3 to 49.3).  While the control group wellbeing scores changed very little over the four week period, the test group improved dramatically to 78% moderate wellbeing and 11% high wellbeing at the end of the four week study. No group scored a high level of wellbeing at the start of the study (see Fig. 6 b+c).

Limitations

Level of Participation

The level of participation was low amongst the student cohort across both studies. When students are participants, identifying a low stress period during the academic year becomes challenging. A contributory factor in Study 1 may have been that it was conducted during the Covid-19 pandemic when students faced a time of uncertainty and increased mental health challenges. It was also conducted prior to examinations, a potentially anxietyinducing time for students. This was reflected in the high scores at baseline for depression, anxiety and stress in Study 1. The experience gained in Study 1 informed the design of Study 2 and the collaboration with the School of Dental Science provided the opportunity to expand the cohort of potential participants to 500. While 58 participants started the study, 33 fully completed the 4 week study. To mitigate the level of attrition in both studies, future research could offer an incentive such as a raffle prize to those participants who complete the study.

Mode of application 

Clinical studies investigating the efficacy of an inhalation aromatherapy intervention frequently employ room diffusion, oil infused gauze or a nasal aromastick yielding positive results. In room diffusion, the essential oils are placed in a water vapourised diffuser, for example to measure the impact on the levels of stress and anxiety on patients undergoing stress-inducing medical procedures [14,57]. In the present study (Study 1, room diffusion), the product was used every day by 58% of the participants and on most days by a further 37% of participants. A bowl of hot water (63%), a room diffuser (32%) or a tissue (5%)were used by the participants. However, the use of a bowl of hot water was reported to be cumbersome by participants. This may have contributed to the low level of participation amongst the student cohort (“Bowl of hot water was not the best way to use the product as it became cold quickly and the aroma became much less noticeable”/ “Difficult to get an aroma using a bowl of hot water”).

Following the experience gained on room diffusion in Study 1, a decision was made to use a different mode of application in Study 2. Aromasticks have been used for over 15 years in UK cancer hospitals where the complementary therapy team of aromatherapists offer patients a choice of a single essential oil or a blend of oils,  which is then sealed in a portable nasal stick for individual use [64-66]. These aromasticks have shown to alleviate the distressing side effects of chemotherapy and radiation treatments and are an empowering tool for patients to use in symptom management [27]. In the current study 7% of participants used the aromastick many times a day, 22% every day and a further 61% reported to have used them most days. “Enjoyed using the product & taking deep breaths”/ “I enjoyed using it very much and I feel like during stressful moments it helped me take a step back and just breathe and realise everything would be okay” / “I think the product definitely calmed me in the moment but its effects were short term”). A growing number of pilot clinical studies in the USA and Germany have reported a positive improvement on stress levels when using commercially manufactured aromastick brands to measure their effects on stress, anxiety, cognitive performance and post-procedural nausea. These commercial products contain a blend of oils and have the added advantage of containing a consistent and precise dose for each test intervention [59,67-69].

Duration of Study

To fully evaluate the potential benefits of the aromatherapy intervention, the appropriate length of the study was considered. In previous studies, the period of exposure to the essential oils varies considerably. It can range from a short burst of inhalation over a few seconds or minutes using an aromastick or oil infused cloth [13,68] to room diffusion overnight when investigating sleep quality [70]. A recent study reported room diffusion for two hours every night over a six month period examining the effect on cognitive function [71]. An aromatherapy product used for an extended period may yield more significant data and facilitate a more comprehensive assessment of its efficacy. The period of intervention in  Study 1 was one week and Study 2 is was extended to a four week period. However, the individual scores from week 2 to the end of week 4 did not change much. The largest increase was from baseline (T=0) to week 2 of the study.  A follow up longitudinal study would be worthy of consideration to evaluate the sustainability of the observed effects.

Pre-screening of participants

Ten of the thirty respondents in Study 1 who completed the first DASS questionnaire received scores of less than 10 for depression, anxiety and stress which would be considered ‘normal’. Although all products were selected through randomisation, a similar situation emerged from the analysis of Study 2 as the control group reported a higher level of wellbeing at the start of the four-week study compared to the test group whose wellbeing scores were considerably lower (Fig. 6 b-c). In future studies, a pre-screening questionnaire to identify and exclude those in the ‘normal’ category, and include those within the mild to moderate categories would benefit the quality and significance of the results. 

Conclusion

The results of both these pilot studies demonstrated that a test formulation of essential oils increased wellbeing and reduced depression, stress and anxiety levels in a young adult population. Both studies reported a statistical significance in favour of the test intervention for depression (p=0.04) and stress in Study 1 (room diffusion) (p=0.0291) and in increased levels of wellbeing in Study 2 (aromastick) (p=0.002). While the studies were small in sample size (n=17; n=33), a clear trend was observed in favour of the test group for the duration of both studies. The findings were encouraging and indicated that the use of aromatherapy had a positive impact on the mental health of the student cohort. 

The robust design of these double-blind studies and the use of validated measurement tools strengthened the results. Unlike other clinical investigations using aromatherapy, the formulations of both test and control had a precise dosage of the essential oils, used a specific plant species and were prepared by a clinical aromatherapist. It is recommended that in future aromatherapy research studies this methodological approach be integrated into an aromatherapy protocol that forms part of evidence based research.

Acknowledgments: Fiona Hedigan was awarded a four year postgraduate scholarship by the Irish Research Council under the Employment-Based Postgraduate Programme 2020

Grant number: Irish Research Council Award 2020- Project ID: EBPPG/2020/114. 

Ethical Considerations: Both pilot studies were granted ethical approval by the School of Pharmacy and Pharmaceutical Sciences Research Committee (Study 1) and the Dental Science Research Ethics Committee (Study 2), at the University of Dublin, Trinity College.

Conflict of Interest: Fiona Hedigan is also employed by Fiona Hedigan & Associates Limited. She is conducting her postgraduate research as part of a collaboration agreement between the Enterprise Partner (Fiona Hedigan & Associates Limited) and Trinity College Dublin.

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