What Does the Research Say About Essential Oils?
Although essential oils have been used therapeutically for centuries, there is little published research on many of them. However, this is beginning to change as more scientific studies on essential oils are conducted around the world.
Clinical studies are currently underway in Europe, Australia, Japan, India, the United States, and Canada. Many of these studies describe the remarkable healing properties of various oils.
Who is doing the research?
A significant body of research on essential oils has been conducted by the food, flavoring, cosmetics, and tobacco industries. They are most interested in the flavor, mood alteration, and preservative qualities of essential oils. Some of these companies have also conducted extensive research on the toxicity and safety of essential oils.
Although much of this research is proprietary and not generally available to consumers, some of it has made its way into cosmetic and plant product journals. These journals are important sources of information as we accumulate a growing body of knowledge on essential oils.
Most of the studies that have been published in the English language scientific literature have been conducted in laboratories and they have not been tested on humans, but this is changing.
What are some issues in conducting research on essential oils?
There are some unique issues in conducting research on essential oils.
- Essential Oils Are Not Standardized: The chemistry of essential oils is influenced by the local geography and weather conditions, as well as the season and time of day when the plants are harvested, how they are processed, and how they are packaged and stored. Each plant is unique in its chemistry so essential oils are never exactly the same-this is different from pharmaceutical drugs that are synthetically reproduced to be identical every time.
Essential oils can be altered to achieve standardization (for example, a certain chemical that was found to be at a lower concentration in the whole oil in a particular year can be added to make it the same percentage as last year's batch). The problem with standardized essential oils is that they are no longer natural, genuine, and authentic. This variability in essential oils by time, place and conditions is a big challenge to conducting valid research. Currently the International Standards Organization sets standards for each essential oil that include a range of acceptable concentrations for its major chemical constituents.
- It Is Difficult to Conduct Blinded Studies with Aromatic Substances: Typical research studies involve testing two groups-one group gets an experimental substance and another group gets a placebo substance (this group is referred to as the "control" group). When using aromatic substances, it is very difficult to conduct a blinded study. Some researchers have used masks or other barriers to blind participants. Other researchers have used alternate scents assumed to have no therapeutic properties as controls. These approaches are problematic, however, because people associate smells with past experiences. Thus, it is difficult to account for individual variation in how essential oils affect people.
- It Is Difficult to Get Approval and Funding for Research on Essential Oils: Essential oils have been used on humans for thousands of years. As a result, they don't fit into the conventional clinical science approach of testing a substance in the lab first, then on animals, and then on humans. As a result, if a researcher proposes to test an essential oil with humans first, they may be turned down. This is because research review boards tend to approve research studies that follow the more usual scientific research path.
Many conventional drug studies are funded by the pharmaceutical industry. There is little motivation for these companies to fund research on natural plant substances because they cannot easily be patented, limiting the potential for profit. Thus, finding funding for essential oils studies can be challenging.
- It Is Difficult to Tell What Caused the Outcome: In conventional research studies, it is important to be able to determine exactly what caused the outcome. In essential oil therapy, the oils are sometimes applied with massage, which makes it difficult to tell whether or not the outcome was due to the essential oil alone, or the massage, or the combination. Also, essential oils are composed of hundreds of chemical constituents, and it is hard to determine which ones may have produced the desired effect.
What does the research say?
Research studies on essential oils show positive effects for a variety of health concerns including infections, pain, anxiety, depression, tumors, premenstrual syndrome, nausea, and many others. The resources on this page are meant to highlight a few examples.