The practice of administering plant-derived essential oils on the skin, via inhalation of vapors, or internally via ingestion for supposed healing power is commonly called aromatherapy. The oils for aromatherapy are described as “essential” to refer to the volatile, aromatic components that some people describe as the “essence” of the plant source, which represents the plant’s “life force,” “spirit,” or soul. Aromatherapy is thus rooted in vitalism, which is described in The Skeptic’s Dictionary as:
… the metaphysical doctrine that living organisms possess a non-physical inner force or energy that gives them the property of life.
Vitalists believe that the laws of physics and chemistry alone cannot explain life functions and processes.”
Perhaps the most famous notion of vitalism is “The Force” in Star Wars, but different names for the hypothesized vital force, such as chi, prana, and innate intelligence, are used as part of the medical folklore in various real-world cultures. Vitalism is a significant component of religious belief systems.
Some people have strong religious beliefs in the healing power of essential oils, as suggested in the Amazon description for David Stewart’s book Chemistry of Essential Oils Made Simple: God’s Love Manifest in Molecules (2005):
This solidly scientific book is anchored in scripture and easy to understand, [sic] It will give you an appreciation of both the scientific and spiritual bases of healing by prayer and anointing with oils.
Anchoring in scripture is not what I expect of a solidly scientific book, but perhaps Stewart’s book can be cited as evidence against the notion of non-overlapping magisteria.
Regulation of Essential Oils in the United States
The marketing of essential oil products in the United States is subject to regulation by the Consumer Product Safety Commission (CPSC), the Food and Drug Administration (FDA), and the Federal Trade Commission (FTC).
CPSC regulates a wide range of consumer products to ensure that consumers are not exposed to unreasonable risks of injury or death. Essential oils are somewhat similar to products like air fresheners and scented candles, which are regulated by the CPSC.
Essential oils are also somewhat similar to cosmetics and/or drugs, which are two categories of products regulated by the FDA. Intended use is key to FDA product regulation. When products (other than soap) have as their intended use cleansing the body or making a person more attractive, they are regulated as cosmetics. When products are labeled for therapeutic purposes involving changing the structure or function of the body, they are then subject to FDA’s authority to regulate drugs. In the United States, drugs require FDA approval prior to marketing. Investigational New Drugs (INDs) must be shown to perform well in three phases of increasingly rigorous study to receive FDA approval. It is illegal to market unapproved drugs.
The FTC regulates advertising of consumer products. The FTC can take regulatory action when essential oils are advertised with false or misleading claims.
The Aromatherapy Market
According to a market research report published in 2018:
- The largest regional market for aromatherapy is North America.
- Aromatherapy companies include: doTERRA International, Edens Garden, Frontier Natural Products Co-op., G Baldwin & Co., Mountain Rose Herbs, Ouwave Aroma Tech(shenzhen)Co., Ltd., Plant Therapy Inc., Ryohin Keikaku Co., Ltd. (Muji), Thann-Oryza Co., Ltd., Young Living Essential Oils and Zija International.
- “… the global aromatherapy market was valued at US$ 1,413.4 Mn in 2016, and is expected to reach US$ 3,226.2 … .”
- Application to the skin is the most common mode of delivery of essential oils, but aerial diffusion methods are growing in popularity.
- Applications are used for skin and hair care, relaxation, pain management, scar management, sleep management, and overall health and well-being.
- Essential oils are touted as natural healers and are used by aromatherapists and spas for healing pain, injuries, sleep enhancement, skin care, and allergies.
- Historic uses for aromatherapy include treating skin rashes, eczema, burn treatment, and acne.
The National Association for Holistic Aromatherapy (NAHA) a “non-profit association devoted to the holistic integration and education of aromatherapy into a wide range of complementary healthcare practices including self-care and home pharmacy.” It states that internal use of essential oils is common throughout the world, but it acknowledges that it is often done without sufficient knowledge of safety concerns.
NAHA warns: “If essential oils are used internally, we recommend doing so under the guidance of a knowledgeable health professional.” I’m not sure how consumers can make consistent, valid determinations of which health professionals who promote internal use of essential oils is sufficiently knowledgeable.
… aromatherapy is an unlicensed profession in the United States. Many aromatherapy practitioners hold a license in another occupation, e.g. nursing, massage therapy, esthetics, naturopathy, acupuncture, etc.
Aromatherapy has also been administered in conjunction with acupressure. Acupressure is a variant of acupuncture that uses manual pressure instead of needle insertion at specific points of the body to supposedly enable various types of healing throughout the body. Although some acupuncture enthusiasts claim that acupuncture has real therapeutic effects and suggest various biological mechanisms of action, acupuncture, like aromatherapy, is rooted in vitalism.
In 2015, BMC Complementary and Alternative Medicinepublished a paper on a study that randomly assigned six institutions that specialize in the care of dementia patients in Taiwan to have their patients receive one of three interventions intended to prevent agitation among patients: (1) aroma-acupressure with 2.5 percent lavender oil at five specified acupuncture points (56 patients), (2) aromatherapy with 2.5 percent lavender oil at five unspecified points (73 patients), or (3) a control intervention of usual care(57 patients). Two institutions were assigned to each intervention. Outcome measurements were taken using an inventory for evaluating agitation and a heart rate variability (HRV) analyzer. The researchers reported that both aromatherapy groups had lower agitation scores than the control group and at some follow-up periods the aroma-acupressure group had the most favorable autonomic nervous system activity related to stress response at some, but not most, follow-up times.
You might be confused about how the aroma-acupressure intervention differed from the aromatherapy intervention. So am I.
Focus on Alternative and Complementary Therapies published my critique of the study. I noted that: (1) the study was a quasi-experiment rather than a true experiment since institutions rather than individuals within each institution were randomly assigned to the intervention conditions; (2) there were notable differences among the groups in terms of age, gender, and diagnostic categories among the groups, and agitation scores at the start of the study; (3) patients were not blinded to what intervention they were receiving (which meant that they could have been responsive simply to extra attention they were getting in the two aromatherapy groups); (4) the researchers didn’t establish that HRV is valid for measuring autonomic nervous system function; and (5) the researchers didn’t establish why it is clinically meaningful to consider HRV when attempting to control agitation of dementia patients.
Improvement should have been expected for the patients since they were selected to be in study because of their high agitation scores. Whenever research participants are selected based on having extreme scores on an imperfectly reliable measure, upon retesting, more of the research participants are likely to have less extreme than more extreme scores. This phenomenon is known as regression toward the mean.
It is not clear that apparent positive findings reflect differential effects of interventions rather than differences in patient populations of different facilities, the overall care given at different facilities at various times, extra attention received in intervention groups compared control groups, measurement bias, excess statistical power, and/or the result of considering a large number of endpoints instead of focusing on testing a few clearly specified hypotheses.
Systematic Reviews of Aromatherapy
Many therapeutic claims have been made for aromatherapy. It’s a huge task to scrutinize them carefully. While I have not systematically reviewed the individual studies or systematic reviews of individual studies assessing the safety and benefits of aromatherapy, I can summarize at least some systematic reviews.
Several systematic reviews have found significant shortcomings of available evidence or have indicated causes for concern:
- An overview published in 2012 of systematic reviews of aromatherapy concluded: “… the evidence is not sufficiently convincing that aromatherapy is an effective therapy for any condition.” (p. 257)
- A 2012 systematic review of case reports and case series reporting adverse effects (AEs) of aromatherapy identified seventy-one patients that experienced adverse effects and concluded: “… aromatherapy has the potential to cause AEs which can occasionally be serious. Their frequency remains unknown.” (p. 147) Dermatitis was the most commonly reported adverse effect. The oils that were most commonly implicated were lavender, peppermint, tea tree, and ylang-ylang.
- A systematic review published in 2012 of eleven clinical trials of aromatherapy for behavioral problems of dementia reported several positive effects but noted flawed research designs in most of the studies so that “… available evidence in the literature is not sufficient to make a conclusive claim.” (p. 380)
- In 2012, authors of a systematic review of aromatherapy treatment of hypertension concluded: “The existing trial evidence does not show convincingly that aromatherapy is effective for hypertension.” (p. 37)
- A systematic review published in 2011 based on sixteen randomized controlled trials of aromatherapy used for treating symptoms of anxiety found that most of the studies indicated positive effects and no adverse events were reported, but the researchers noted: “The quality of the studies’ design prevented drawing firm valid conclusions as to the clinical efficacy of aromatherapy.” (p. 106)
More recent systematic reviews emphasizing (but, unfortunately, not always limited to) rigorously controlled randomized clinical trials have been inconclusive due to limitations in designs of studies of reviewed. Examples are reviews that addressed studies of effects of aromatherapy on dysmenorrhea, depressive symptoms, symptoms associated with burns, stress, agitation in dementia, and sleep. The least rigorous of these reviews provided optimistic spins on the findings despite limitations noted in the studies they scrutinized.
A 2016 systematic review and meta-analysis of clinical trials of aromatherapy on pain had favorable results, but it relied on studies that combined aromatherapy as an add-on in combination with usual treatments while control groups had no special intervention. Studies with such designs are biased in favor of intervention groups for generating favorable subjective outcomes because they send the message to research participants receiving the add-on that they are getting something special while control groups get no such message. A 2017 systematic review of aromatherapy for postoperative pain found insufficient evidence to support its use.
A systematic review paper published in 2018 that scrutinized fifteen randomized controlled trials, two uncontrolled trials, and five quasi-experiments (comparison group studies that aren’t tightly controlled) of inhalation or (in six of the studies in the review) massage aromatherapy treatment of hemodialysis complications reported that aromatherapy had favorable effects of anxiety, fatigue, itching, pain at the hemodialysis puncture site, sleep quality, depression, stress, and headache. The authors did not discuss effect size, so it is unclear from their review how much impact the aromatherapy interventions had on hemodialysis complications. Statistical significance does not mean that false discoveries are unlikely and does not imply that positive effects are strong enough to make a practical difference for patients. Quality scores for the studies reviewed ranged from only 2.2 to 3.5 on a five-point scale.
From what I can tell, none of the studies had a control group that received the attention, care, comfort, and bodily contact of massage, but without the particular aromas of the recommended oils. Massage might be more responsible than any particular oils for symptomatic relief.
Nonetheless, the authors offered this favorable, though tentative, conclusion:
Considering the complications and heavy cost of managing complications in patients undergoing hemodialysis, it appears that aromatherapy can be used as an inexpensive, fast acting and effective treatment to reduce the complication in hemodialysis patients subject to further study to assure the safety and effectiveness of the procedures.
The Bottom Line
In Trick or Treatment: The Undeniable Facts About Alternative Medicine (2008, W. W. Norton & Company), authors Simon Singh and Edzard Ernst offered this conclusion about aromatherapy:
Aromatherapy has short-term ‘de-stressing’ effects which can contribute to enhanced wellbeing after treatment. There is no evidence that aromatherapy can treat specific diseases. (p. 299)
They also wrote that since the relaxing effects of aromatherapy massage are usually short lived, they are “therefore of debatable therapeutic value.”
I think their assessment holds up well ten years later.
I acknowledge that some people enjoy the aromas of essential oils. As long as aromatherapy is offered inexpensively to consumers, I’m not sure that rigorous studies are needed to verify modest, nonmedical claims such as: people experience transient mood improvement when they are exposed to aromas they like. Perhaps there is a role for some approaches to aromatherapy in providing care and comfort to people with specific health challenges. But I see no reason to expect any type of aromatherapy to alter the course of any disease or have vitalistic actions such as “balancing body energies,” as promoted by some enthusiasts.
Aromatherapy isn’t necessarily inexpensive. Essential oils have been promoted through multilevel marketing, which inflates product prices so that distributors at each level can receive a portion of payments. Consumers should be wary when distributors of multilevel marketing companies hype essential oils and other products using testimonials.
I acknowledge that many aromatherapists strive to be responsible and professional, and they succeed, at least in some ways. For example, NAHA notes safety considerations regarding skin, eyes, and during pregnancy when administering essential oils.
Some aromatherapy advocacy groups have taken strong, commendable stands against practitioners who have promoted unsafe uses of essential oils and have made unfounded claims for aromatherapy in enhancing bodily processes or relieving specific health problems. My next column will focus on one notorious essential oil huckster and his record as a diploma mill naturopath in promoting bogus healing methods to people with serious diseases.