Aromatherapy for stress reduction in healthy adults: a systematic review and meta-analysis of randomized clinical trials

• Stress may lead to physical diseases such as heart disease, stomach ulcers, hypertension, etc.
• Aromatherapy is the therapeutic use of essential oils from plants via the skin or the olfactory system.
• One previous overview suggested that aromatherapy may reduce pain and improve psychological health.
• Five randomised clinical trials met our inclusion criteria, and most of them had high risk of bias.
• There is limited evidence suggesting that aroma inhalation may be effective in controlling stress.

The aim of this review was to systematically assess the effectiveness of aromatherapy for stress management. Seven databases were searched from their inception through April 2014. RCTs testing aromatherapy against any type of controls in healthy human person that assessed stress level and cortisol level were considered. Two reviewers independently performed the selection of the studies, data abstraction and validations. The risk of bias was assessed using Cochrane criteria. Five RCTs met our inclusion criteria, and most of them had high risk of bias. Four RCTs tested the effects of aroma inhalation compared with no treatment, no aroma, and no odour oil. The meta-analysis suggested that aroma inhalation has favourable effects on stress management (n = 80; standard mean difference (SMD), −0.96; 95% CI, −1.44 to −0.48; P < 0.0001; I2 = 0%). Three of included RCTs tested aroma inhalation on saliva or serum cortisol level compared with control and meta-analysis failed to show significant difference between two groups (n = 88, SMDs −0.62; 95% CIs −1.26 to 0.02, P = 0.06, I2 = 46%). In conclusion, there is limited evidence suggesting that aroma inhalation may be effective in controlling stress. However, the number, size and quality of the RCTs are too low to draw firm conclusions.