Essential Oil Research Limitations and Funding

Short answer. Aromatherapy research does exist, but reviewers keep finding the same weaknesses. That is why we label most findings as limited and rarely say an oil "works".

What the reviews say

A review of reviews of aromatherapy found most systematic reviews were of poor methodological quality, and for none of the conditions was the evidence convincing. [1] NCCIH reaches a similar place for specific uses: for insomnia, little rigorous research has been done, so it is not known whether aromatherapy helps. [2] These are summaries by their authors, not the last word, and newer trials continue to appear.

The usual limits

Which oil, which part of the plant, which batch

Oils are mixtures, and trials do not always say exactly what was used. The tea tree review notes that commercial oil is variable, though no obvious differences in bioactivity had been noted so far. [6] For other oils we did not find a source in this search that measured how often trials report oil composition. Proper evidence not found (we searched PubMed for essential oil trials and reporting of chemical composition). This is why one result should not be carried across oils, batches or ways of use: inhaling, massage and skin application are different things.

Who pays for the research

NCCIH lists a lack of independent funding and testing among the limits of the lavender research. [3] That points to a real concern, but it does not tell us how large the problem is across oils.

For the wider question, a Cochrane review of 75 studies on drugs and devices found industry-sponsored studies more often had favorable efficacy results than other studies. [7] That review did not look at essential oils. We searched PubMed for aromatherapy or essential oil trials and their funders, sponsors or conflicts of interest. Proper evidence not found for an analysis of essential oil trial funding. So we cannot say how common company-funded trials are in this field, and we do not claim a funding bias in aromatherapy.

What you can do is check the paper's funding and conflict-of-interest statements, and prefer studies that were tested by independent groups.

What this means for you

• Treat claims such as "clinically proven" with caution and look for the study.
• Do not use oils in place of care from a clinician. Ask a pharmacist or clinician about any health problem.
• Read Human clinical studies and Human vs lab research for how to read the studies, and Claims checked for common marketing claims. Open questions are listed in Unanswered questions.