Unanswered Questions About Essential Oils

Short answer. Quite a lot is still open. This page lists the questions where the sources we read say the answer is unknown, and says plainly where we found no answer.

Does aromatherapy help for common uses?

Unsettled. NCCIH says it is unclear whether aromatherapy with lavender oil has benefits for anxiety, stress, depression symptoms, some types of pain, sleep or insomnia. [1] A review of reviews found the evidence was not convincing for any condition it examined. [2] Label: insufficient evidence for most uses. See limits of the research.

How much of the effect is expectation?

Open. In one study, suggestion about an odor changed heart rate and skin conductance, and the authors concluded that expectations play a significant role in odor-evoked mood change. [3] A scientific analysis found credible evidence that odors can affect mood, physiology and behavior. [4] Separating smell itself from belief is hard to do. See How scent works.

Do lavender and tea tree oils affect hormones in children?

Not settled. Case reports link breast growth in prepubertal children with products containing lavender, and in four children breast growth dissipated when the products were stopped. [5] The authors say whether lavender oil's estrogenic potency is enough to cause these effects is unknown. [5] NCCIH notes it is unclear whether the lavender was responsible, since the condition can have many causes. [1] A 2016 report of three boys advises considering exposure to estrogenic substances such as lavender in such cases. [6] A 2024 lab and computer study found some oil components bind steroid-making enzymes, but this was not a study in people. [7] The same authors say limited knowledge exists about potential detrimental side effects. [7] See Lavender oil: skin reactions and hormone questions.

What are the long-term effects of daily use?

Proper evidence not found. We searched PubMed for long-term safety reviews of essential oil exposure and read the adverse-effect reviews below. The case-report review says the frequency of adverse effects remains unknown. [8] The most common reported effect was dermatitis, and the reported cases included one death. [8]

What happens in the air of a home when oils are diffused?

Only early data. A pilot study simulated tea tree oil in a household using two diffuser types. [9] In one of the two surveys, terpene levels were generally an order of magnitude higher than in the other. [9] This is one oil and one setup; it does not tell us about health effects. See Diffusers, indoor air and exposure.

How common is contamination?

Not known from the sources we read. A New England Journal of Medicine report describes four non-travel-associated melioidosis cases linked to an imported aromatherapy spray. [10] The outbreak resulted in 2 deaths. [11] This is one documented event. We did not find a source measuring how often contaminated products reach buyers. See Purity and adulteration.

Do oils interact with medicines?

For lavender, NCCIH says there are theoretical reasons to suspect interaction with some sedative drugs, which matters before surgery. [1] Ask a pharmacist, and see Essential oils and medicines and how interactions work.

Do lab findings translate to people?

Often untested. See Human vs lab research.