It shouldn’t be surprise that not all ingredients have been studied equally. While researchers are working to better understand the effects of both natural and synthetic chemicals on humans and animals, some things currently have more research behind them than others.
Lavender oil is one of those ingredients that has limited research about certain crucial questions. After a case study suggested that it might have estrogenic effects that caused gynecomastia (breast growth) in three pre-pubescent boys, many articles referenced it as estrogenic. Critics of the study, as well as the study itself, called for further research.
Another, more recent study has cast doubt on the idea that lavender is estrogenic, and is an excellent reminder of why it’s important to industriously study the ingredients we use every day. While these studies are not enough to make a definitive conclusion, this recent study should give rise to the idea that lavender oil might not be estrogenic, and we need to conduct further studies to better understand the issue.
What Does it Mean to Be “Estrogenic”?
“Estrogenic” usually means that a substance — which can be synthetic or natural — is structurally or functionally similar to estrogen, effectively acting like or influencing the body’s natural estrogen. The broad term for these estrogen-affecting substances are “xenoestrogens,” and those specifically found in plants are “phytoestrogens” (Polish Journal of Veterinary Science, 2008; Cancer, Epidemiology, Biomarkers, & Prevention, 2001).
Xenoestrogens are a subset of what are called “endocrine disrupting chemicals” (EDCs) or “endocrine disruptors” (NIH). These interfere with the endocrine system, responsible for hormones, changing how it works, typically in a negative and/or unintended way. Endocrine disruptors work in or affect the endocrine system in different ways, such as mimicking, blocking, or interfering.
These can be found both in nature (in the form of plants) and synthetically (in certain medications, pesticides, personal care products, plastics, etc.). Some of these are used to intentionally affect the endocrine system, such as hormone therapy.
The Source of Initial Alarm about Lavender Oil
One of the oft-cited pieces of research looking at the estrogenic effects of lavender is a 2007 case study of three pre-pubescent boys with gynecomastia (breast growth). In these cases, three boys between the ages of 4- and 10-years-old experienced breast growth and all used personal care products containing lavender oil or lavender and tea tree oil (The New England Journal of Medicine, 2007). After ceasing lavender- or lavender and tea tree oil-containing products, all three boys’ breast growth issues resolved.
In cellular in vitro tests, the researchers found that lavender and tea tree oil had weak estrogenic and antiandrogenic activity, and suggested that these might be one of the factors in the boys’ gynecomastia. Previous studies have also found that some essential oils have compounds that interact with estrogen receptors (The Journal of Pharmacy and Pharmacology, 2002).
This case study isn’t the definitive word on lavender. The researchers recommended larger studies looking at lavender and tea tree oil. In the meantime, they recommend that doctors inform patients to be cautious about lavender and tea tree oil usage.
A New Study’s Findings on Lavender Oil
Recently, another study contradicted the 2007 study’s findings that lavender was estrogenic. In the study, researchers used uterotrophic bioassays to determine the effects of topical lavender oil on immature female rats. Over a 3-day period, researchers treated four groups (each with 10 rats): a control group treated with corn oil, a positive control group gavaged with 17α-ethinyl estradiol, a group treated with 20 mg/kg of lavender oil, and a final test group treated with 100 mg/kg of lavender oil. Upon measuring body and uterine weights, the researchers concluded that lavender oil had no estrogenic effects (International Journal of Toxicology, 2009).
Because of rats’ short estrous cycle (4-5 days), they typically respond to estrogenic substances in about two days (Uterotrophic Assay Standard Evaluation Procedure, 2011).
The lavender issue is an excellent illustration of why it’s important to test something numerous times. Preliminary results like those in the case study should be a catalyst for future research, such as the rat study.
The initial study suggested a link between lavender oil and gynecomastia in pre-pubescent boys, but there are numerous criticisms, including the limited information about the other ingredients in the boys’ personal care products, and the concentration of oils in these products. The recent study on rats throws considerable doubt on the idea that lavender is estrogenic.
However, one study isn’t a final answer, and it’s important to do more research on the potential estrogenic effects of lavender to further illuminate us on the issue. We’ll be sure to keep you posted!