2. Methods
2.1. Criteria for including studies in this review
2.1.1. Types of studies
Randomized controlled trials (RCTs) and quasi-RCTs were included. Trials that did not provide detailed results will also be excluded. Dissertations and abstracts will be included if these contain sufficient details for critical evaluation. No language restriction will be imposed.
2.1.2. Types of participants
The studies evaluated healthy participants were included. The studies conducted with subjects with chronic or psychological diseases; pregnant subjects, children, or animals were excluded.
2.1.3. Types of interventions
We included those trials using the aroma inhalation, aromatherapy massage with any types of essential oil alone or as a combined therapy of the aroma inhalation, aromatherapy massage with a conventional therapy versus the same conventional therapy. Aromatherapy is defined as the therapeutic use of essential oils from plants. There were no limitations on the number of essential oils used, the dosage, the forms of aromatherapy or the duration of the treatment.
2.1.4. Types of outcome measures
The following outcome measures will be assessed based on analyses of the data obtained in the included trials:
2.1.4.1. Primary outcome
Subjective stress level with visual analogue scale, numerical rating scale or verified questionnaire for measuring stress level was determined.
2.1.4.2. Secondary outcomes
(1)
Cortisol level (saliva or plasma or serum);
(2)
Adverse effects likely to be related to treatment.
2.2. Search methods for identifying the studies
2.2.1. Electronic searches
The electronic searches were performed using Pubmed, the Cumulative Index to Nursing and Allied Health Literature (CINAHL), EMBASE, and the Cochrane Central Register of Controlled Trials (CENTRAL). We also searched three Korean databases (the Research Information Service System (RISS), DBPIA, and the Korean Studies Information Service System (KISS)). Languages were limited to English and Korean. In addition to electronic databases, grey journals such as dissertations, news articles, presentation materials, etc. were searched manually.
2.2.2. Search strategy
The searching term was (aromatherapy OR aroma* OR (essential oil)) AND (stress).