Abstract

Introduction: Behavioral and psychological symptoms of dementia (BPSD) is the most prominent and distressing manifestation for older persons with dementia (PWD) and caregivers. Aromatherapy has demonstrated its effectiveness in managing BPSD in various studies. However, previous studies and systematic reviews have obtained inconsistent findings, and a review of qualitative studies is yet to be conducted. Method: A mixed-methods systematic review with a convergent segregated approach was performed to evaluate the effectiveness of aromatherapy in improving the BPSD and quality of life (QoL) of PWD and in relieving the distress and burden of caregivers, as well as its safety for PWD. Both published and unpublished quantitative and qualitative studies written in English and Chinese between January 1996 and December 2020 were retrieved from 28 databases, including MEDLINE, EMBASE, and Web of Science, based on the prespecified criteria. The methodological quality was assessed by using critical appraisal tools from the Joanna Briggs Institute. Quantitative synthesis, qualitative synthesis, and integration of quantitative and qualitative evidence were performed. Results: A total of 12 randomized controlled trials, 10 quasi-experimental studies, and 2 qualitative studies were included in the review. Some inconsistent findings regarding the effectiveness of aromatherapy in reducing the severity of BPSD were observed. Some studies reported that aromatherapy significantly improved the QoL of PWD and relieved the distress and burden of caregivers, promoted a positive experience among caregivers, and had very low adverse effects on PWD (with aromatherapy inhalation reporting no adverse effects). Conclusion: Aromatherapy, especially in the inhalation approach, could be a potentially safe and effective strategy for managing BPSD. However, more structuralized and comparable studies with sufficient sample size, adherence monitoring, and sound theoretical basis could be conducted to obtain conclusive findings.

© 2021 The Author(s). Published by S. Karger AG, Basel

Introduction

Dementia is an acquired brain syndrome marked by a considerable cognitive decline from a previous level of performance in cognitive domains that cannot be attributed to any other mental disorder; it affects the independence of individuals in their daily activities [1, 2]. According to the World Health Organization, about 5%–8% (>55 million) of the elderly aged 60 years and above are living with dementia, and dementia has emerged as one of the major causes of disability and dependency among the elderly worldwide [3, 4]. Behavioral and psychological symptoms of dementia (BPSD) is a term coined by the International Psychogeriatric Association (IPA) in 1996 [5] to refer to a diverse range of symptoms of “disturbed perception, thought content, mood, or behavior that frequently occur in patients with dementia” [6]. According to previous studies, over 90% of older persons with dementia (PWD) exhibit at least one BPSD symptom at any stage of their disease [7-11]. Behavioral symptoms of BPSD include aggression, agitation, and sleep disorders, whereas psychological symptoms include anxiety, depression, and apathy [5, 12].

BPSD is the most prominent and distressing manifestation of dementia for PWD and caregivers [13-15]. For PWD, BPSD is associated with worsening cognitive functions and progression of dementia [16] that may reduce their social functions and quality of life (QoL) [17], increase their susceptibility to abuse and neglect [18], and expose them to physical harm [19] and secondary complications, such as falls and fractures [20], which would ultimately lead to their hospitalization or institutionalization [21]. Meanwhile, formal and informal caregivers need to deal with both the cognitive deterioration of PWD and their BPSD [13]. Unlike the downward trends in cognitive and functional status in dementia, BPSD may fluctuate episodically during the progression of the disease, which introduces challenges in caring PWD and increases the burden and distress faced by caregivers [22-24] that harm their physical, psychological, and emotional well-being [25]. Studies on formal and informal caregivers reveal that the BPSD severity has a significant positive correlation with the degree of caregiver distress and burden [25-28]. Therefore, effective management of BPSD should be prioritized by healthcare professionals and caregivers to reduce its negative impacts on PWD, alleviate the level of distress and burden among caregivers, and preserve the well-being of both PWD and caregivers [29].

With their high safety and low association with adverse events, nonpharmacological strategies have received much attention as safe methods for BPSD management [30] and have been recommended as a first-line approach in various studies and dementia guidelines [30-34]. Aromatherapy, as a nonpharmacological strategy that relies on sensory stimulation [35], has evolved from herbal and botanical medicine with at least 6,000 years of history [36]. Contemporarily, aromatherapy is defined as a natural treatment through a variety of approaches (e.g., inhalation, topical application, and massage), with the use of essential oils extracted from aromatic plants, to balance, harmonize, and promote the health of the body, mind, and spirit [37-39]. Analyses of systematic reviews and clinical guidelines on nonpharmacological strategies for managing BPSD highly recommend aromatherapy as the best strategy due to its good-quality patient-oriented evidence [40]. Aromatherapy acts on the body through olfactory stimulation or percutaneous absorption of the chemicals in essential oils [36, 41-43] and has been clinically used in BPSD management for over 20 years. Clinical studies show that aromatherapy can improve BPSD symptoms, such as sleep disturbance [44, 45], agitation [46, 47], depression [47, 48], and aggression [49, 50], but the theoretical basis for the implementation of this treatment has not been described. A systematic review of 11 randomized controlled trials (RCTs) that evaluated the effects of aromatherapy on dementia revealed that aromatherapy, except for oral intake, could effectively and safely reduce the frequencies of BPSD among PWD and could be considered a potentially effective strategy for BPSD management [51].

However, a Cochrane Review involving 13 RCTs revealed that the included trials produced inconclusive evidence regarding the effects of aromatherapy on the BPSD and QoL of PWD, and the distress and burden of caregivers; moreover, the safety of aromatherapy for PWD was not evaluated in the studies [15]. In addition, previous reviews only focused on published RCTs and ignored other quantitative, qualitative, and unpublished studies, which may lead to publication bias and generate incomplete evidence. Therefore, a mixed-methods systematic review (MMSR) with a convergent segregated approach following the Joanna Briggs Institute (JBI) methodology [52] for published and unpublished quantitative and qualitative studies was conducted to comprehensively evaluate the effectiveness and safety of aromatherapy.

Aim and Objectives

This review aims to systematically identify and review the present evidence on the effectiveness of aromatherapy in BPSD management for both PWD and caregivers, and its safety for PWD. The objectives of this review are to evaluate the effectiveness of aromatherapy in improving the BPSD severity and QoL of PWD, and the distress and burden of caregivers, as well as the safety of this treatment among PWD.

Methods Search Strategy

A systematic literature search was conducted in December 2020 to identify both published and unpublished quantitative and qualitative studies written in English and Chinese, between January 1996 and December 2020 (after the term BPSD was introduced by IPA). The Population, Intervention, Comparison, and Outcome (PICO) search model was used to identify the search terms (Table 1). A total of 14 English databases (Academic Search Ultimate, AgeLine, AMED, APA PsycINFO, British Nursing Index, CINAHL Complete, EMBASE, Health & Medical Collection, MEDLINE, Ovid Emcare, PubMed, Research Library: Health & Medicine, Scopus, and Web of Science) and 6 Chinese databases (Airiti Library-CEPS Journals, CJN, CMCC, HyRead, NCL Periodical Information Center, and WanFang Data-Journal) were included in the search for published studies, and 8 databases (Airiti Library-CETD Theses, Dissertations & Theses @ Chinese University of Hong Kong, Google Scholar, Grey Literature Report, Networked Digital Library of Theses and Dissertations Global ETD Search, PQDT OPEN, ProQuest Dissertations & Theses, and WanFang Data-Chinese Dissertations Database) were included in the search for unpublished studies. The reference lists and bibliographies of the included studies and literature reviews were screened to identify additional relevant studies. The review was registered with the International Prospective Register of Systematic Reviews (PROSPERO; registration no. CRD42021239188).

Table 1.

PICO model for identification of English and Chinese search terms

Study Selection

After the literature search, duplicates, articles published before 1996, and articles not written in English or Chinese were removed from the results. The titles and abstracts of the remaining articles were screened by 2 reviewers based on the inclusion and exclusion criteria described in Table 2, and the full text of screened articles was retrieved for further assessment by 2 reviewers. Discrepancies were resolved through discussion.

Table 2.

Inclusion and exclusion criteria for quantitative and qualitative studies

Methodological Quality Assessment

The methodological quality of the included studies was independently appraised by 2 reviewers using the JBI critical appraisal tools [53]. Discrepancies were resolved through discussion.

Data Synthesis and Integration

This review followed the convergent segregated approach to synthesis and integration following the JBI methodology for MMSR [52]. Quantitative and qualitative syntheses were separately conducted followed by the integration of the resultant evidence.

The quantitative data were analyzed according to the study design, characteristics of the participants, interventions applied, and outcome measurements. For those studies with RCT or a pretest-posttest control (PPC) design and whose findings were described as means and standard deviations (SD), the effect sizes dppc2 were calculated using the formula proposed by Morris [54]. An effect size of 0.2 was interpreted as small, 0.5 was interpreted as moderate, and 0.8 was interpreted as large [55]. The quantitative data from studies with similar designs, interventions, and outcome measurements, where possible, were pooled in a statistical meta-analysis using Review Manager 5.4 [56]. The mean change from the baseline to postintervention and the SD of the mean change were used in the meta-analysis. If the outcome was measured using different instruments, the standardized mean difference and 95% confidence interval (CI) were calculated. Otherwise, the weighted mean difference and 95% CI were calculated. The statistical heterogeneity was assessed by Higgins I2 [57], where I2 ≥50% indicates substantial heterogeneity [57], and a random-effects model was used for the statistical pooling. Otherwise, a fixed-effects model was used.

The qualitative data were analyzed according to the study design, characteristics of the participants, and implementation of aromatherapy. The qualitative data, where possible, were analyzed using the meta-aggregation approach [58], which involved the aggregation or synthesis of findings to generate a set of statements that represent such aggregation. The findings were assembled and categorized based on the similarities in their meanings, and these categories were then synthesized to produce a comprehensive set of synthesized findings.

The findings of the quantitative and qualitative syntheses were then configured. These findings were juxtaposed to check if the findings from the quantitative studies were supported or contradicted by those from the qualitative studies.

Results Study Selection

A total of 8,262 articles were identified from the databases, and 2 additional relevant articles were sourced from reference lists and bibliographies. After the screening, 45 potential articles were identified. The full texts of these articles were retrieved and reviewed, and 20 articles were eventually excluded from the review, in which 3 conference abstracts being excluded were describing interventional studies using aromatherapy on PWD with BPSD, and all of them reported positive effect in managing BPSD symptoms such as agitation, disturbed behavior, and sleep disturbance [59-61]. Finally, a total of 24 studies, as described in 25 English articles (in which one study was described in 2 articles), were included in the review, among which 22 were quantitative studies (12 RCTs and 10 quasi-experimental studies) and 2 were qualitative studies. The Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) flowchart of the study retrieval and selection process is presented in Figure 1.

Fig. 1.

PRISMA flowchart of study retrieval and selection process. PRISMA, Preferred Reporting Items for Systematic Reviews and Meta-Analyses.

Methodological Quality

The methodological quality of 12 RCTs was appraised using the JBI Critical Appraisal Checklist for RCTs [62] (Table 3). All RCTs satisfied more than half (≥7) of the criteria in the checklist. However, among the criteria, only half of the studies (n = 6) achieved true randomization in assigning participant and treatment groups of similar baselines. Moreover, in the treatment assignment, only 2 studies (16.7%) were able to blind their participants, and 4 studies (33.3%) were able to blind the treatment deliverers. The 10 quasi-experimental studies were appraised using the JBI Critical Appraisal Checklist for Quasi-Experimental Studies [63] (Table 4). Eight studies (80%) satisfied more than half (≥5) of the criteria in the checklist, and 2 studies (20%) satisfied only 4 criteria. Among the criteria, only 2 studies (20%) had control groups, and 3 studies (30%) had multiple measurements of the outcome both at the pre- and postintervention. The 2 qualitative studies were appraised using the JBI Critical Appraisal Checklist for Qualitative Research [64] (Table 5), and both of them satisfied more than half of the criteria (≥6). However, both studies did not state their philosophical or theoretical premises, did not locate the researchers culturally or theoretically, and did not address the influence of the researcher and vice versa.

Table 3.

Methodological quality of RCTs

Table 4.

Methodological quality of quasi-experimental studies

Table 5.

Methodological quality of qualitative studies

Synthesis of Quantitative Data Description of Studies

Among the 22 quantitative studies, 12 were RCTs, of which 9 had a 2-armed design and 3 had a 3-armed design, 8 used a parallel design, and 4 used a crossover design. Ten studies were quasi-experimental, of which 4 used a 1-group pretest-posttest design, 4 used a within-subjects design, 1 used a nonequivalent control group design, and 1 used a nonequivalent control group crossover design. The summaries of the RCTs and quasi-experimental studies are listed in Table 6. These studies were conducted in the USA (n = 6), UK (n = 4), Japan (n = 3), Australia (n = 2), Taiwan (n = 2), Switzerland (n = 1), Turkey (n = 1), Israel (n = 1), Korea (n = 1), and Hong Kong (n = 1). Most of these studies (55%, n = 12) were conducted in long-term residential care facility settings (e.g., nursing homes and care and attention homes), 6 in hospital inpatient settings (e.g., psychogeriatric wards and inpatient units), 2 in daycare settings (e.g., daycare centers and outpatient day programs), 1 in home-based settings, and 1 in both hospital and nursing homes.

Table 6.

Summary table of included quantitative studies

Participants

A total of 855 PWD with mild-to-severe dementia were included in these studies, while 1 study included 28 caregivers. The PWD sample size ranged from 7 to 186, and 59% (n = 13) of the included studies had a sample size of <30. The mean age of PWD ranged from 66.8 to 86.2 years (no data from Cameron et al. [65]), with a mean of 81.2 years (SD = 9.0). About 52% of these PWD were female (no data from Cameron et al. [65] and Snow et al. [66]).

Interventions

All studies delivered aromatherapy interventions, but their theoretical bases were not described. These interventions varied substantially in terms of their approaches, essential oils, frequencies, dosages, durations, deliverers, and settings.

Inhalation

Twelve studies delivered aromatherapy through inhalation. Among these studies, 7 used lavender (Lavandula angustifolia) essential oil alone in 100% [67, 68], 3% [69], 2% [70], and unspecified [71-73] concentrations. Two studies used different essential oils across various stages of the intervention [66, 74]. One study used 100% sweet orange (Citrus sinensis) essential oil for daytime inhalation and 100% lavender essential oil for nighttime inhalation [75]. One study used an essential oil blend with an unspecified concentration [76]. The remaining one study allowed the participants to select between 100% lavender essential oil and other 100% essential oil blends [45]. Aromatherapy inhalation was delivered using different methods. In all, six studies used diffuser [67, 70-72, 75, 76], 3 studies placed a cotton ball or fabric sachet with essential oil or dropped the essential oil on or near the collar of the participants [66, 68, 74], 1 study placed a cotton napkin with essential oil on tables [73], 1 study wrapped a towel with essential oil around the pillow of the participants [45], and 1 study sprayed essential oil mist on the chest of the participants [69]. The frequencies ranged from twice a week to 4 times a day, with each inhalation administered with 1–6 drops of essential oil and lasted from 20 min to overnight. The intervention duration lasted from 8 days to 6 months, and 2 studies involved 2 or 6 weeks of follow-up. Two studies were delivered in long-term residential care facilities by trained formal caregivers [67] or the researcher [45], 2 were delivered in hospital inpatient settings by a nurse [75] or aromatherapist [71], and others were conducted in long-term residential care facilities (n = 4), hospitals (n = 2), or daycare centers (n = 1) with unspecified deliverers.

Topical Application

Five studies delivered aromatherapy through topical application. Among these studies, 3 used lavender essential oil with 30% [77], 2.5% [48, 78], and unspecified [79] concentrations; and 2 used Melissa (Melissa officinalis) essential oil with 10% [80] or <2% [65] concentration. The frequencies ranged from once to 3 times a day, and 1 study delivered aromatherapy whenever an agitated behavior was reported. Each session lasted from 1 to 15 min. The intervention duration lasted from 3 days to 4 months, and only one study involved 3 weeks of follow-up. Two studies were delivered in long-term residential care facilities by trained care assistants [80] or nurses [77], 2 studies were delivered in hospital inpatient settings by nurses [65, 79], and 1 study was conducted in long-term residential care facilities [48, 78] with an unspecified deliverer.

Massage

Four studies delivered aromatherapy through massage. Among these studies, 1 used lavender essential oil with an unspecified concentration [71], and 3 used different essential oil blends with concentrations ranging from 1% to 6% [47, 81, 82]. The frequencies ranged from once a week to once a day, with each session lasting from 10 min to 1 h. The intervention duration lasted from 2 to 8 weeks. Two studies were delivered in long-term residential care facilities by trained research assistants [47] or the researcher and the aromatherapist [82], 1 was delivered in hospital inpatient settings by aromatherapists [71], and 1 was delivered in both hospitals and long-term residential care facilities by the researcher and nurses with aromatherapist certificates [81].

Other Approaches

Three studies delivered aromatherapy using other approaches. One study delivered aromatherapy twice a day for 6 weeks during which 3% lavender essential oil was delivered through mist spray and a 5-min hand massage by the researcher and trained research assistants in long-term residential care facilities [69]. One study delivered aromatherapy 3 times a day for 4 weeks through a combination of 3 times per week massage with essential oil blends by an aromatherapist and a once-a-day inhalation of 6 drops of 100% lavender essential oil through a diffuser by family caregivers at homes [83]. One study (described in 2 articles) involved a daily delivery of 2-min aromatherapy acupressure for 4 weeks using 2.5% lavender essential oil in long-term residential care facilities [48, 78]. Two of these studies had 3 or 6 weeks of follow-up [48, 69, 78].

Outcomes Change in BPSD Severity for PWD

Nine studies used the Neuropsychiatric Inventory (NPI) [84] to measure neuropsychiatric symptoms of BPSD. After receiving aromatherapy, NPI decreased significantly in 5 studies compared with the control conditions, in which the aromatherapy interventions were delivered by the inhalation of 100% lavender or sweet orange essential oil with moderate effect (n = 3, dppc2 = 0.674–0.763) [67, 68, 75], by the topical application of 10% Melissa essential oil with large effect (n = 1, dppc2 = 0.979) [80], and by massaging an essential oil blend and inhaling 100% lavender essential oil (n = 1) [83]. Four studies reported no significant difference in NPI after delivering aromatherapy through massage, inhalation, or topical application with essential oil blends or Melissa essential oil compared with the control conditions [45, 65, 79, 82]. In those studies adopting a crossover design, no significant period and sequential effects were observed [67], and a significant increase in NPI was noted during the washout period [65].

Nine studies used the Cohen-Mansfield Agitation Inventory (CMAI) [85] to evaluate agitation. Four studies found that aromatherapy significantly relieved agitation compared with the control conditions, in which aromatherapy interventions were delivered by the inhalation of 100% lavender essential oil with small effect (n = 1, dppc2 = 0.244) [67], by the topical application of 10% Melissa or 2.5% lavender essential oil with moderate to large effect (n = 2, dppc2 = 0.728–0.979) [78, 80], by acupressure with 2.5% lavender essential with near moderate effect (n = 1, dppc2 = 0.491) [78], and by massaging essential oil blends and inhaling 100% lavender essential oil (n = 1) [83]. Three studies that delivered aromatherapy through massage, inhalation, or topical application of 1%–6% lavender or essential oil blends revealed a decrease in agitation in the aromatherapy group; however, such change was not significant compared with the control conditions [47, 69, 82]. Two studies showed that the inhalation of 100% lavender essential oil [66] or topical application of <2% Melissa essential oil [65] had no significant treatment effect compared with the control condition. In those studies adopting a crossover design, no significant period and sequential effects were reported [67], and a significant increase in CMAI was noted during the washout period [65]. For the study with a 3-week follow-up, the follow-up CMAI score was higher than the postintervention score [78].

Three studies used the Cornell Scale for Depression in Dementia (CSDD) [86] to evaluate depression. Two studies reported a significant decrease in depression among those PWD receiving aromatherapy through acupressure, topical application, or massage with 2.5%–6% lavender essential oil with large effect (dppc2 = 0.87–1.583) [47, 48]. One study that delivered aromatherapy by massage with a 1% to 2% essential oil blend reported improvement in depression, but such improvement was not significant compared with the control condition [82]. For the study with a follow-up, the follow-up CSDD score was higher than the postintervention score [78].

Two studies used the Pittsburgh Agitation Scale (PAS) [87] to evaluate agitation. One study showed a significant improvement in agitation after the inhalation of 2% lavender essential oil compared with the control condition [70]. One crossover study showed no significant difference in agitation after the topical application of <2% Melissa essential oil compared with the control condition, and the PAS score significantly increased during the washout period [65].

Ten studies used other instruments to evaluate BPSD severity. Five studies [45, 72, 73, 77, 81] showed significant improvements in BPSD after a topical application of 30% lavender essential oil, inhalation of lavender essential oil or essential oil blends with unspecified concentrations, or massage with 2% essential oil blends. One study found that the effect of essential oil blend inhalation on BPSD management widely varied, with 60% of the participants reporting a significant decrease in their disturbance behavior and the rest reporting no changes or an increase in such behavior [76]. For the other 4 studies, no significant difference was reported in anxiety, psychotropic drugs used, and behaviors related to BPSD compared with the control or preintervention condition [71, 74, 79, 88].

Change in QoL for PWD

The effects of aromatherapy on the QoL of PWD were examined in one study by using the QoL parameters from Dementia Care Mapping. The aromatherapy group receiving a 4-week topical application of 10% Melissa essential oil reported significant improvements in their QoL, with a significant reduction in the time they spend in social withdrawal behaviors, and a significant increase in the time they spend doing constructive activities [80].

Change in Caregiver Distress

The scores for caregiver distress in NPI were reported in 2 studies, both of which observed a significant reduction in caregiver distress after the PWD inhaled 100% lavender or sweet orange essential oil delivered by caregivers and/or massaged with essential oil blends by an aromatherapist [75, 83].

Change in Caregiver Burden

One study used the Zarit Burden Interview [89] to measure the change in caregiver burden and reported a significant decrease in caregiver burden after the PWD were massaged with essential oil blends by an aromatherapist and inhaled 100% lavender essential oil delivered by family caregivers [83].

Safety of Administering Aromatherapy among PWD

The possible adverse effects of aromatherapy were reported in 3 studies. One participant who received a topical application of 10% Melissa essential oil experienced diarrhea for 2 days [80], whereas 2 participants withdrew from the study due to an unspecified discomfort after being massaged with 6% essential oil blend [47]. Sleepiness, nausea, skin irritation, gait instability, and falls were reported by those participants who received a topical application of lavender essential oil [79]. Ten studies [48, 67-69, 71, 72, 75, 77, 78, 82, 83] reported negligible or no adverse events among the participants who received aromatherapy, and the remaining 9 studies [45, 65, 66, 70, 73, 74, 76, 81, 88] have not assessed the safety of aromatherapy on PWD.

Meta-Analysis

Given inadequate reporting or the high heterogeneity among the approaches and contents of aromatherapy, only 2 RCTs had similar designs and sufficient data for meta-analysis. These studies used aromatherapy inhalation with 100% lavender essential oil as their intervention and NPI for their outcome measurement [67, 68]. The meta-analysis revealed the significant positive treatment effect of aromatherapy inhalation of 100% lavender essential oil (MD = −7.11, 95% CI = −10.15 to −4.08, p < 0.0001) and a low degree of heterogeneity (χ2 = 0.05, p = 0.83, I2 = 0%) (Fig. 2).

Fig. 2.

Forest plot of meta-analysis to 2 RCTs with aromatherapy inhalation of 100% lavender essential oil using the results of NPI as outcome measure. RCTs, randomized controlled trials; NPI, Neuropsychiatric Inventory; CI, confidence interval; SD, standard deviation.

Synthesis of Qualitative Data Description of Studies

Two qualitative studies were included in the review, both of which were action research studies that investigated the experiences and perceptions of caregivers toward the use of aromatherapy among PWD with BPSD. One of these studies was performed in nursing homes in Norway [90], whereas the other was performed in a multicultural dementia day-care center in Australia [91]. Table 7 summarizes these studies.

Table 7.

Summary table of included qualitative studies

Participants

The participants included 24 PWD residents and 12 nurses from 4 nursing homes [90] as well as 16 PWD clients, 16 family caregivers, and 7 staff from one dementia day-care center [91].

Aromatherapy Implementation

In these 2 studies, the caregivers were involved in the design, implementation, and evaluation of aromatherapy programs for PWD to manage their BPSD. In Johannessen [90], the nurses from nursing homes delivered overnight aromatherapy inhalation to the residents by placing 12–15 drops of lavender essential oil into a diffuser. In Kilstoff and Chenoweth [91], the family caregivers and day-care staff delivered hand massage to PWD with essential oil blends for 10–15 min. Both studies did not describe the safety issues or adverse effects of aromatherapy on PWD.

Meta-Aggregation

After analyzing the full texts of these 2 qualitative studies, 46 findings related to the effectiveness of aromatherapy in managing BPSD were identified. These findings were aggregated into 6 categories and further aggregated into 2 synthesized findings (Table 8).

Table 8.

Synthesized findings of meta-aggregation

Synthesized Finding 1: Effectiveness for PWD

Aromatherapy has an overall positive effect on PWD in terms of BPSD management and other aspects.

Category 1.1. Effectiveness in BPSD Management

Most of the caregivers in both studies [90, 91] claimed that BPSD, such as sleep disturbance, anxiety, agitation, and restlessness, significantly decreased among those PWD who received aromatherapy. However, some caregivers also reported either a slight increase in aggression, anger, sulking, and irritation, unclear effects, or no effects at all. Overall, aromatherapy may positively contribute to reducing BPSD among most of the PWD in these studies.

Category 1.2. Effectiveness in Other Aspects

Most of the family caregivers perceived that the PWD looked forward to and enjoyed aromatherapy. They became more alert, relaxed, calm, cheerful, interested in their surroundings and social activities, and showed improvements in their communication and functional abilities after receiving aromatherapy [91].

Synthesized Finding 2: Effectiveness for Caregivers

The caregivers claimed that they benefited from aromatherapy, that their relationships with PWD were improved, and that they were interested to learn more about the treatment.

Category 2.1. Effectiveness in the Emotion and Caregiving Aspects

The caregivers reported that aromatherapy helped them focus on their own well-being, develop greater coping mechanisms and a sense of control, and calm themselves down. However, some of them reported initial difficulties in caregiving when the PWD became more alert and inquisitive after receiving aromatherapy, but the perceived benefits of aromatherapy for these PWD overrode such initial negative effect [91]. In sum, aromatherapy generates an overall positive effect on the emotion and caregiving for caregivers.

Category 2.2. Effectiveness in Improving Relationships between Caregivers and PWD

The family caregivers reported improvements in their relationships with their PWD relatives after delivering aromatherapy [91]. They perceived aromatherapy as a vehicle for them to reconnect with their PWD relatives and improve their personal relationships.

Category 2.3. Effectiveness in Promoting Interest in Aromatherapy

The nurses reported that their participation in the aromatherapy program and the effectiveness of aromatherapy for the PWD raised their interest in essential oils and inspired them to continue using aromatherapy after the completion of the program [90].

Integration of Quantitative and Qualitative Evidence

More than half of the quantitative studies (68%, n = 15) reported improvements in BPSD severity after receiving aromatherapy compared with the control conditions, with 12 studies reporting a statistically significant difference between the aromatherapy and control conditions. However, 7 quantitative studies reported no improvements. The findings from the quantitative studies were supported by qualitative findings given that most of the caregivers in the qualitative studies reported the positive effects of aromatherapy in reducing BPSD, including sleep disturbance, agitation, and anxiety, even if some caregivers reported a slight increase in irritation, aggression, anger, and sulking. Apart from BPSD management, most caregivers from the qualitative studies reported other positive effects of aromatherapy on PWD, such as improvements in their functional abilities, alertness, communication, interest in their surroundings, and feelings of enjoyment and relaxation, all of which contribute to their QoL as reflected in a quantitative study that measured the QoL of PWD [80].

The quantitative studies reported a significant reduction in distress and burden among those caregivers who administered aromatherapy. These findings were supported by those of qualitative studies, wherein caregivers described their experiences and perceptions toward how they could benefit from aromatherapy. They generally described aromatherapy as a soothing and pleasant experience. Specifically, by delivering aromatherapy to PWD, they improved their understanding about the needs of PWD, learned to develop better coping mechanisms, and improved their relationship with the PWD. Moreover, by actively participating in the aromatherapy program and experiencing the positive effects of aromatherapy on PWD, these caregivers became more interested in knowing how to use aromatherapy in other ways, such as in reducing their own distress and burden.

While 3 quantitative studies reported that aromatherapy may have adverse effects [47, 79, 80], 10 reported negligible or no adverse events [48, 67-69, 71, 72, 75, 77, 78, 82, 83] after completing the aromatherapy program. However, these safety issues were not described in the qualitative studies.

Adherence Monitoring

Only 4 studies described the methods they used to monitor the adherence or the adherence rate of the delivered aromatherapy interventions. These methods included weighing the bottles with aromatherapy products [80], using massage and inhalation monitoring form [83], or monitoring by the researcher [90]. The adherence rates were reported as either full adherence [83] or 96.4% ± 7.9% adherence [79].

Discussion Effectiveness and Safety of Aromatherapy

Consistent with the results of the recent Cochrane Review [15], the studies included in this review failed to reach a consensus with regard to the effectiveness of aromatherapy in reducing BPSD severity.

More than half of the included studies (68%, 15 quantitative and 2 qualitative studies) reported that aromatherapy positively contributed to reducing BPSD severity, with 12 studies reporting a statistical significance with effect sizes ranging from small to large (dppc2 0.244–1.583). Meanwhile, 7 quantitative studies reported no significant differences between the aromatherapy and control conditions, which may be due to the high diversity in their intervention approaches, essential oils, dosages, frequencies and duration of aromatherapy interventions, and methodologies and instruments for outcome measurement. Meanwhile, those studies that did not report positive findings had relatively small sample sizes (5–22 participants in each intervention/control condition) compared with other studies (7–73 participants in each condition), thereby increasing their chances of producing false nonsignificant results for intervention with a smaller effect [92, 93]. Furthermore, most of these studies did not monitor adherence to the treatment. Poor adherence and nonadherence may reduce the effects of aromatherapy and increase the risk of producing false nonsignificant results for the intervention.

Only one quantitative study measured the change in QoL after receiving aromatherapy [80] and reported that such treatment reduced social withdrawal and promoted constructive activities among the PWD. The positive effects of aromatherapy on the functional abilities, communication, social activities, and mood of the PWD as described in qualitative studies [90, 91] may contribute to such changes in QoL.

Two quantitative studies measured the changes in distress and/or burden among those caregivers who administered the aromatherapy interventions, and both of these studies reported a significant decrease in caregiver distress and/or burden after the delivery of the intervention [75, 83]. In the qualitative studies, the caregivers reported positive experiences and perceptions toward the program and reported that aromatherapy benefited them in both the emotion and caregiving aspects and improved their relationships with the PWD [90, 91], all of which may contribute to reducing their distress and burden. These improvements may also be attributed to how BPSD severity of PWD is reduced by aromatherapy, and the olfactory stimulation or percutaneous absorption of essential oils into the bodies of caregivers during their delivery of the intervention [36, 41-43]. Therefore, these findings suggest that delivering aromatherapy could decrease the burden or distress of caregiving.

Only 3 studies reported the possible adverse effects of the topical application or massage of essential oils, but most of these effects were only mild and temporary (e.g., sleepiness, nausea, and skin irritation). Meanwhile, those studies that delivered inhalation reported no adverse effects of aromatherapy. Aromatherapy has short-term effects as reflected in the absence of period and sequential effects or increases in BPSD severity during the washout period in crossover studies [65, 67] and during the postintervention follow-up assessments [48, 78]. These findings agreed well with those of human and animal laboratory studies that focused on the pharmacokinetics of essential oils, wherein essential oil chemicals were completely removed from the body in <4 h [94-97]. Therefore, aromatherapy, especially inhalation, is a safe intervention given its very low risk of producing prolonged adverse effects on the health of the receiver.

Implications for Research and Practice

The most frequently used aromatherapy approach in the reviewed studies was inhalation (62.5%, n = 15), among which 73.3% (n = 11) reported the positive effect of aromatherapy on BPSD and 46.7% (n = 7) reported a statistical significance between the aromatherapy and control conditions. None of these studies reported any adverse effects related to aromatherapy inhalation. With the above evidence, aromatherapy inhalation is considered the safest intervention for reducing BPSD severity. However, the delivery methods, essential oils, dosages, frequencies, and duration of aromatherapy inhalation in these studies show high heterogeneity. Therefore, the most effective components of aromatherapy inhalation warrant further examination.

However, evidence on the effectiveness of aromatherapy in reducing BPSD severity among PWD was generally inconsistent, while evidence on its effects on the QoL of PWD and the distress and burden of caregivers was limited. More structuralized and comparable studies could then be conducted with sufficient sample size and adherence monitoring to obtain conclusive findings regarding the effectiveness of aromatherapy in managing BPSD.

The included studies and previous laboratory studies revealed that aromatherapy only has short-term effects, but none of the included studies reported the theoretical basis for such intervention. Theory is “a set of concepts, definitions, and propositions that explain or predict events or situations by illustrating the relationships between variables” [98] and is recommended in the development and implementation of health-related interventions [99, 100]. Theory can identify the constructs and facilitate the specification of potential active ingredients in order to improve the effects of an intervention, facilitate the accumulation of evidence, and improve one’s understanding of the mechanisms behind changes [101, 102]. Future studies may develop interventions based on appropriate theories and empirical evidence to maintain the positive long-term effects of aromatherapy.

Strengths and Limitations

This systematic review was conducted by extensively searching for published and unpublished literature in academic databases to maximize the possibility of identifying and including studies related to the use of aromatherapy in BPSD management. By synthesizing both quantitative and qualitative findings, this article presents a highly comprehensive review of the current evidence related to the provision of aromatherapy to PWD experiencing BPSD.

However, this review has several limitations. First, this review only considered those studies written in English or Chinese. Therefore, some related studies written in other languages were excluded from the search. Second, this review was limited by the poor methodological quality of some studies due to their lack of relevant information. However, this limitation of the included studies was acknowledged and made explicit through their methodological quality scores. Third, given the wide variety in the approaches and components used in aromatherapy and the outcome measures used in the included studies, performing a meta-analysis of most of the included quantitative studies was impossible. Fourth, this review also considered unpublished studies that did not undergo peer review. Therefore, the validity of findings from these studies cannot be guaranteed. Fifth, despite receiving help from a librarian in sending requests to both local and oversea libraries, the full texts of several articles that might be relevant to the review were not retrieved for further assessment.

Conclusion

This MMSR aims to synthesize evidence from both published and unpublished quantitative and qualitative studies by using a convergent segregated approach [52] to evaluate the effectiveness and safety of aromatherapy in BPSD management. Evidence regarding the effectiveness of aromatherapy in reducing BPSD severity was inconsistent due to the high heterogeneity in the delivery approaches, outcome assessment methods, small sample sizes, and lack of adherence monitoring in the included studies. Some of these studies reported significant improvements in the QoL of PWD and the distress and burden of caregivers, positive experiences from the caregivers who delivered aromatherapy, and low adverse effects (with aromatherapy inhalation having no adverse effect at all) of the treatment.

Therefore, aromatherapy, especially in the inhalation approach, is a safe and effective strategy for BPSD management. However, structuralized and comparable studies with sufficient sample size, adherence monitoring, and a sound theoretical basis could be conducted to obtain conclusive findings regarding the effectiveness of aromatherapy in BPSD management.

Acknowledgments

The authors would like to acknowledge the Chinese University of Hong Kong for supporting the postgraduate study undertaken by the first, third, and fifth authors; Dr. Kai Chow Choi for providing statistical consultation; and university librarians’ suggestions in database searching and assistance in retrieving articles for this review.

Statement of Ethics

As this is a systematic review, ethical approval and consent to participate were not applicable. This review has been submitted for registration on PROSPERO (registration no. CRD42021239188).

Conflict of Interest Statement

The authors have no conflicts of interest to declare.

Funding Sources

This review has received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors.

Author Contributions

Under the supervision of C.W.H.C and I.K.Y.W., B.S.Y.L. designed the study, analyzed the data, and wrote the initial draft of the manuscript, and B.S.Y.L. and Y.H.U.Y. conducted literature searching, methodological quality appraisal, and data extraction. All the authors participated in revising and final approval of the manuscript.

Data Availability Statement

All data generated or analyzed during this study are included in this article. Further enquiries can be directed to the corresponding author.

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