Are Essential Oils Endocrine Disruptors?

An ENDO 2018 presentation that linked essential oils to gynecomastia in prepubertal boys caused a bit of an uproar in the spring. The study authors detail what their research means, why certain populations should be mindful of essential oil use, and the importance of future studies.

A study presented this past March at ENDO 2018 in Chicago raised yet another concern in the growing problem of endocrine-disrupting chemicals (EDCs), providing further evidence of a suspected link between prepubertal gynecomastia and regular exposure to lavender or tea tree oil. According to researchers, key chemicals in these common plant-derived oils act as EDCs, which may cause prepubescent boys to develop enlarged breast tissue.

Lavender (LO) and tea tree oil (TTO) are among the so-called “essential oils” that have become popular in the United States as alternatives for medical treatment, personal hygiene and cleaning products, and aromatherapy. Various consumer products contain lavender and tea tree oil, including some soaps, lotions, shampoos, hair-styling products, cologne, and laundry detergents.

“Our society deems essential oils as safe,” says study researcher J. Tyler Ramsey, a postbaccalaureate research fellow at the National Institute of Environmental Health Sciences (NIEHS), part of the National Institutes of Health. “However, they possess a diverse amount of chemicals and should be used with caution because some of these chemicals are potential endocrine disruptors.”

Male gynecomastia occurring before puberty is relatively rare, but a growing amount of cases have been reported to coincide with topical exposure to lavender and tea tree oil. Kenneth Korach, PhD, the senior scientist for the new NIEHS EDC study, previously found laboratory evidence that lavender and tea tree oil showed endocrine-disrupting activities.

In that study, published in the New England Journal of Medicine in 2007, Korach and his team concluded that once the boys stopped using the products, the gynecomastia resolved. “Furthermore,” they wrote, “studies in human cell lines indicated that the two oils had estrogenic and antiandrogenic activities. We conclude that repeated topical exposure to lavender and tea tree oils probably caused prepubertal gynecomastia in these boys.”

“The current study is based on our original observations published in the NEJM linking lavender and tea tree oils to the incidence of male prepubertal gynecomastia,” Ramsey and Korach write in an email to Endocrine News.  “At the time, we tested whether lavender or tea tree oil had any hormonal activities and found that they were estrogenic and also antiandrogenic.”

“Our society deems essential oils as safe. However, they possess a diverse amount of chemicals and should be used with caution because some of these chemicals are potential endocrine disruptors.” — Tyler Ramsey, a postbaccalaureate research fellow at the National Institute of Environmental Health Sciences (NIEHS), part of the National Institutes of Health, Research Triangle Park, N.C.

Surprising Outcomes

Under Korach’s direction, Ramsey and his NIEHS colleagues went a step further. From the hundreds of chemicals that comprise lavender and tea tree oil, they selected for analysis eight components that are common and mandated by the International Standard Organization for inclusion in the oils. “We wanted to study the essential oils to determine what specific components in lavender and tea tree oil could potentially possess hormonal activity,” Ramsey and Korach write. “We also wanted to know which of the components would have either or both of the estrogenic or antiandrogenic activities, as well as the mechanisms by which these components activate estrogen receptor alpha and the androgen receptor. In our previous studies, only lavender and tea tree oil were examined and the precise mechanisms by which they act were not determined.”

Four of the tested chemicals appear in both lavender and tea tree oils: eucalyptol, 4-terpineol, dipentene/limonene, and alpha-terpineol. The others were in either oil: linalyl acetate, linalool, alpha-terpinene and gamma-terpinene. Using in vitro experiments, the researchers applied these chemicals to human cancer cells to measure changes of estrogen receptor- and androgen receptor-target genes and transcriptional activity. All eight chemicals demonstrated varying estrogenic and/or anti-androgenic properties, with some showing high or little to no activity, the investigators reported. Ramsey says these changes were consistent with endogenous, or bodily, hormonal conditions that stimulate gynecomastia in prepubescent boys.

“There were a few surprising outcomes that we did not expect when we first started these experiments,” Ramsey and Korach write. “Many of the components differentially elicited hormonal activity and some had no activity at all. These are interesting results because it shows that some components, not all, are potential endocrine disruptors.”

Providing Clarity

Of course, whenever a study like this is made public, it will make some waves. When Endocrine News first broke the news on social media, the account received a few strong responses, demanding to know what this means for people who use essential oils or expressing concerns about the study itself. A press release from the Australian Tea Tree Industry Association pointed out what it perceived as flaws in the study and expressed its disappointment by saying, “this sensationalization of data from Ramsey et al. at ENDO 2018 has caused undue concern for consumers of [tea tree oil] around the world.”

The group goes on to write in its opinion, “Since the 2007 NEJM paper…multiple investigators have demonstrated the flaws in linking TTO (as well as LO and other essential oils) to endocrine disruptor activity.”

Indeed, the Research Institute of Fragrance Materials in 2013 published a paper in the International Journal of Toxicology that disputed Korach and his team’s 2007 findings. However, other studies have confirmed that the oils had hormonal activity.

Still, Ramsey and Korach are confident in their data. And they’re not looking to ruin the essential oils industry; they’re looking to raise awareness about what chemicals are found in “essential” products people use every day. When asked about any pushback to their current work, they only offer that they have addressed many of these concerns in the full manuscript. “When the manuscript is published, we hope it will provide clarity to those with questions.”

Lingering Questions

Ramsey and Korach acknowledge that what was presented at ENDO and the subsequent publication isn’t the final word on the health effects of essential oils. Their work warrants further investigation, and there are more questions to answer.

Many of the chemicals Ramsey, Korach, and their team tested appear in at least 62 other essential oils. Another cause for concern is that essential oils are available without a prescription and are not regulated by the U.S. Food and Drug Administration. The public should be aware of these findings and consider all evidence before deciding to use essential oils.

And no matter the pushback from interested parties, the current evidence shows that oils possess components that are potential endocrine disruptors. The current study provides more evidence between the established link of essential oil use and the potential for development of prepubertal gynecomastia. “Based on clinical case studies,” Ramsey and Korach write, “susceptible individuals that use lavender and tea tree oil products develop prepubertal gynecomastia, but when they stop using the products, the condition subsides.”

  • Bagley is the senior editor of Endocrine News. He wrote about how telehealth improved diabetes outcomes in VA patients in the May issue.



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