April 27, 2018 6 min read

If you use essential oils in any capacity, chances are you’ve heard about new research in the New England Journal of Medicine that linked gynecomastia (prepubertal boys growing breasts) with lavender and tea tree essential oils.

bright body essential oils gynecomastia controversy lavender

The day that the research hit the mainstream media, my husband sent me a CNN article. And shortly thereafter, my friend and fellow boss babe Chelsea Martin (of Luna Aesthetics & Spa) texted me asking me what I thought of it all.

First things first, the most important thing I can say is that SCIENCE IS A LOT MORE NUANCED THAN YOU MIGHT REALIZE. Science is not a black-and-white world, it’s often just as grey as the social sciences in terms of the types of conclusions it can make with certainty. For more on this, check out John Oliver’s wonderful segment on the scientific method here. You won’t regret it.

I’ve looked through the study to get a thorough understanding of its methodology, results, and implications to be able to break down what the study says and whether or not the results should leave you concerned. You see, when most mainstream media outlets report the results on scientific studies, they waaaaay oversimplify the results.

Journalists are usually just reading the abstract and aren’t very sensitive to correlation vs. causation, methodology limitations, and more when they write their own articles. Plus, journalists almost always use a scientifically inaccurate conclusion as the title of their piece (e.g. “New Study Reports that Essential Oils Cause Gynecomastia”) to get clicks and views. If you’ve been wanting to really understand what the fuss is all about, keep reading!

bright body essential oils gynecomastia controversy scientific study review evaluation

We will hit the high points of the study (in terms of hypothesis, methodology, results, and conclusions) followed by my take.

The study was inspired after a physician saw three prepubertal male patients present with gynecomastia. Prepubertal gynecomastia, when contrasted with gynecomastia in adolescents and men, is rare and always considered pathological, meaning there is a negative “disease-causing” factor present.

The cause of prepubertal gynecomastia coincides with either a source of estrogen present, whether it is endogenous (innate/internal) or exogenous (not innate/external). Most patients with prepubertal gynecomastia have normal levels of sex steroids like estrogen, leading doctors to consider external estrogen exposures.

  • Patient 1 was 4 years old. He presented with gynecomastia for 2-3 weeks. All of his bloodwork was within normal ranges. His mother reported using a topical product that contained lavender essential oil. After discontinuing the product, his breast buds completely disappeared.
  • Patient 2 was 10 years old. He presented with gynecomastia for 5 months. Some of his bloodwork (testosterone, free testosterone, and DHEA) were above normal ranges.Those results are inconsistent with high estrogen. He reported using a shampoo and gel containing lavender and tea tree oil every morning. 9 months after discontinuing use of these products, his breast tissue decreased in size but some very small breast buds were still present.
    • If the researchers are asserting that lavender and tea tree oil are estrogenic and anti-androgenic, then why were this patient’s androgen hormones at higher than normal levels?
    • Furthermore, why did his breast buds not completely resolve if the gynecomastia was due 100% to the lavender and tea tree oils?
  • Patient 3 was 7 years old. He presented with gynecomastia for 1 month. The only bloodwork outside of normal ranges were high estrone and low 17-alpha-hydroxyprogesterone, which is consistent with high estrogen. He used lavender-scented soap and intermittently used lavender lotions. A few months after discontinuing use of these products, the gynecomastia completely resolved. However, his fraternal twin brother used the same products and did not report any gynecomastia.

bright body essential oils gynecomastia controversy tea tree

First, let’s address that the “inspiration” for this study included only three subjects. THREE. Any statistician or scientist will tell you that is a painfully small sample size. But study “inspiration” aside, what really irks me about this study is its methodology. They added diluted lavender and tea tree essential oilsto human breast cancer cells grown in vitro. They distinguished between breast cancer cells that produce estrogen receptors and ones that produce androgen receptors.

If the study is trying to understand whether essential oils cause prepubertal gynecomastia, using adult human breast cancer cells is not the best methodology. I’m not exactly sure why they didn’t use healthy breast tissue, since we all understand that cancerous cells do not behave the same way that healthy cells do. I won’t get into the assays that they use because it’s just not necessary to understand the results.

Using the cancerous cells with estrogen receptors, researchers found that both lavender and tea tree oil have estrogenic properties and at high concentrations (less diluted samples), they were toxic to the cells. Of course, anyone who knows essential oils will tell you that proper dilution is key, so that secondary result is a big “no duh.” Both oils affected the expression of estrogen-related genes. Using the cancerous cells with androgen receptors, researchers found that both lavender and tea tree oil have antiandrogenic properties through their modulation of gene expression.

bright body essential oils gynecomastia controversy scientific study review evaluation gene expression DNA RNA

But here’s the real kicker: lavender and tea tree oil showed weak estrogenic and antiandrogenic effects. Yes, the researchers use that exact language in their discussion section. And of course, any good scientist using this study methodology can only say that they suspect that products with these essential oils caused gynecomastia in the three initial patients. I’m not even sure how they can assert that when they are comparing human adult breast cancer tissue with prepubertal boy breast tissue – that is quite a jump not only for the type of cells used but also for the sample size.

The researchers smartly add, “susceptibility to gynecomastia or other manifestations of endocrine disruption may require exposure to a threshold dose of these oils. The threshold might depend on several undefined factors, including the concentration of the oil in a product; the duration, frequency, and quantity of use of the product; and the genetic characteristics of persons exposed.” Genetics might be able to explain why Patient 3’s fraternal twin brother used the same products at the same frequency without developing gynecomastia.

So what’s my take on all this:

  1. This study is FAR from being perfect. With the initial 3 patient sample size and the use of adult human breast cancer cells in vitro, I’m befuddled why this got so much attention other than the fact that it’s very clickbaity.

  2. The results showed weak estrogenic and antiandrogenic effects. You know what has weak estrogenic properties? Flaxseeds, sesame seeds, apricots, oranges, strawberries, peaches, tofu, miso soup, edamame, rye bread, lentils, peas, pinto beans, chickpeas, olives, olive oil, turmeric, thyme, and sage. I don’t think I need to further explain this point.

  3. Dilute your freakin’ essential oils, y’all. No one should ever be using pure essential oils directly on the body. And anytime people tell you to ingest essential oils, you need to be wary and ask for guidance from a medical professional.

  4. Every person is unique. Some people have allergies or are sensitive to certain essential oils that others tolerate no problem. The same goes for the potential hormonal effects of essential oils. If you are noticing trouble with your properly diluted essential oil products, then don’t use them! But just because these three (THREE!) boys showed this correlation (NOT CAUSATION) does not mean that we can make reckless blanket statements like “essential oils cause prepubertal gynecomastia.”

  5. Let me preface this next point with the following: I am a fervent supporter of BOTH traditional medicine and complementary modalities. I wouldn’t be alive today if I didn’t go through months of IV antibiotic therapy for my very serious neurological Lyme disease. However, many traditional medical providers are skeptical of complementary therapies (notice how I say complementary NOT alternative), and I think that at least part of this study was motivated by a desire to discredit these types of therapies. I can’t read the minds of these researchers but we all bring our own internal biases into the laboratory, no matter how hard we try to keep them out.

I hope this was helpful and enlightening. If you’ve heard of any other new research that you’d like me to comb through, tell me about it

Until next time, 



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