Are Lavender and Tea Tree Essential Oils Hormone Disruptors?

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Are Lavender and Tea Tree Essential Oils Hormone Disruptors?


Organic Lavender FlowersOver the years we have received numerous questions regarding the safety of tea tree and lavender oils.

The questions were prompted by information circulating on the internet that originated from a case study published in February 2007 in the New England Journal of Medicine titled "Lavender and Tea Tree Oils May Cause Breast Growth in Boys."

The study suggested that repeated topical use of products containing lavender oil and/or tea tree oil may cause abnormal breast growth in young boys by mimicking the actions of estrogen in the body.

As a parent and a grandparent, I totally understand the fear of doing something to harm your child. But that is why sensational headlines, like “Essential cause male breasts development in young boys" get so much attention.

Sadly, few people read the whole article or even better yet, read the original "evidence." Instead, they simply read the headline and pass it along to friends and family.

Of course, we understand the questions and concerns. It is our unwavering responsibility as parents to protect our children and we take questions like these very seriously.

I have researched this topic quite extensively for personal reasons. I am a breast cancer survivor with estrogen receptor-positive (ER+) cancer. This type of cancer feeds on estrogen, so I am very concerned about any ingredient called an "endocrine disruptor" with effects that mimic estrogen in the body.


Some Science Background

Endocrine System & Essential OilsBefore I get into the discussion of the article mentioned above, a bit of science background is necessary.

  • What is the Endocrine System?
  • What are Estrogens?
  • What are Hormone (Endocrine) Disruptors?

What is the Endocrine System?

The endocrine system plays a role in regulating growth and development, metabolism, tissue function, sexual function, mood, sleep, reproduction and basically influences almost every cell in our bodies.

The endocrine system is a series of different glands in the body that produce and secrete hormones that sent are sent directly into the bloodstream to various tissues in the body where they are needed.

Hormones serve as the body's chemical messengers, transfer information and instructions from one set of cells or tissues to another to tell them what they are supposed to do.

Many different hormones circulate through the bloodstream, but each type of hormone is designed to affect only certain cells.

Each of the glands produces different kinds of hormones that evoke a specific response in cells, tissues, and/or organs located throughout the body. (Picture from Wikipedia)

Any imbalances in the endocrine system could throw off the entire functioning of certain organs and cause disorders, health conditions, and diseases.

For the purpose of this blog, we are looking at a set of hormones called Estrogens.

What is Estrogen?

Estrogens are really a group of hormones that are important for sexual and reproductive development, mainly in women.

Estrogen & Essential OilsThe term "estrogen" refers to all of the chemically similar hormones in this group, which are estrone (E1), estradiol (E2), and estriol (E3).

Estradiol is the most potent and prevalent of the three especially in women of reproductive age. Another form of estrogen called estetrol (E4) is produced only during pregnancy.

In premenopausal women, estrogens are produced mainly in the ovaries, which are part of the endocrine system. Estrogens are also produced by fat cells and the adrenal glands and during pregnancy, estrogens are produced by the placenta.

After menopause, the body still makes small amounts of estrogen. Hormones called androgens are produced by the adrenal gland (located above the kidneys). These androgens are converted to estrogen by an enzyme called aromatase which is produced mainly by fatty tissue.

Although estrogens are often referred to as female sex hormones, they play a major role in many bodily functions.

For example, estradiol circulates throughout the body, including the brain and pituitary gland, and influences reproduction, body weight, and learning and memory.

As a result, many normal functions are compromised when estrogen production decreases if the ovaries are removed or lose their function after menopause.

Also estrogens . . .

  • create female secondary sex characteristics at the onset of puberty
  • help regulate the menstrual cycle
  • during pregnancy, the placenta produces estrogen, specifically the hormone estriol
  • control lactation
  • work with vitamin D, calcium, and other hormones for proper bone formation,
  • play a role in blood clotting
  • help to maintain the strength and thickness of the vaginal wall and vaginal lubrication
  • help control mood

Men produce estrogen as well, but at lower levels than women. Estrogen in males is secreted by the adrenal glands and by the testes.

Estrogen levels change throughout a person's life. For example, estrogen levels increase during puberty and during pregnancy and decrease after menopause. Before menopause, estrogens are produced mainly in the ovaries in women.

As discussed above, after menopause, most estrogens are produced by the adrenal glands and fat tissue.

About 80% of all breast cancers are also sensitive to estrogen, meaning that estrogen actually promotes tumor growth. These cancers are called HR+ (meaning hormone-receptor positive) or (ER+) meaning estrogen receptor-positive breast cancers.

For people with these cancers, treatments to lower estrogen levels or block estrogen production are often used to help prevent cancer recurrence after surgery or to slow cancer growth.


What Are Endocrine (Hormone) Disruptors?

Endocrine disruptors are naturally occurring compounds or synthetic chemicals that may interfere with the production or activity of hormones of the endocrine system. Simply speaking, endocrine disruptors disrupt the normal functioning of the endocrine system.

Any imbalances in the endocrine system could throw off the entire functioning of certain organs and cause disorders, health conditions, and diseases. Many endocrine disruptors are actually synthetic, man-made substances that we encounter every day.

They can be found in:

  • plastic bottles BPA (bisphenol A)
  • metal food cans
  • detergent soaps and shampoos
  • synthetic fragrances (think phthalates)
  • feminine care products
  • cosmetics
  • flame retardants (often found in children's clothing and mattresses)
  • carpeting
  • food (the food chain--animals absorb chemicals around them)
  • heavy metals like lead and mercury (think cookware)
  • toys
  • PVC flooring (think phthalates)
  • pesticides (like DDT and even pesticides in insect repellent)
  • and many, many more

Scientists have also found endocrine disruptors in water and soil samples as well as in our blood, body fat, and even breast milk.

Once released, these hormone disruptors act like chemical messengers. They travel around the body, bind to target receptors on certain cells, and cause cellular changes.

What Are Hormone Disprupters

Endocrine disruptors can have adverse effects on the development, reproductive, neurological, and immune systems in humans and wildlife. Endocrine disruptors cause problems because they can:

  • change or mimic naturally occurring hormones in the body
  • bind to a receptor within a cell and block the natural hormone from binding which then interferes with normal hormone signals
  • block the way natural body hormones or their receptors are made or controlled
  • cause an increase or decrease in hormone production
  • can cause a hormone build-up in fatty tissues
  • source


Are Lavender and Tea Tree Hormone Disruptors?

Natural Organic Tea Tree Oil Skin CareBefore I begin I want to remind everyone that we are all unique.

There are many people with sensitivities or reactions to natural products, ingredients, or plants. I have a friend who could sleep in a bed of poison ivy and come away with no reaction at all. I, on the other hand, need only brush by the "leaves of three" and end up with a full-blown rash everywhere.

The 2007 case study concerning Lavender and Tea Tree oils spread throughout the internet and continues to cause concern today.

I first reviewed this study and researched the information years ago, but recently the study has resurfaced and is now recirculating on the internet.

In this blog, I would like to share my concerns about the study that began the controversy and share what I have learned.

My goal is NOT to convince you that these essential oils are safe. My goal is to encourage you to think for yourself, so you can make your own informed decision.

How the Concern Began

The scare began due to a study published in February 2007 in the New England Journal of Medicine, entitled “Prepubertal Gynecomastia Linked to Lavender and Tea Tree Oils” (by Derek V. Henley, Ph.D. et al: Source)

The article was a case study that documented three cases of gynecomastia in boys aged four to seven who had been using unnamed products which were reported to have contained lavender and/or tea tree essential oils. Once the boys stopped using the products, the breasts went away.

Gynecomastia is swelling of the breast tissue in boys or men, caused by an imbalance of the hormones estrogen and testosterone. Older men, boys going through puberty, and newborns may develop gynecomastia as a result of normal changes in hormone levels.

While working toward my Master's Degree in Biology, I was taught to critically read scientific research. I learned quite early to never accept any discussion about research without taking the time to go back to the original study and ask, "What do I need to know in order to evaluate this piece of research?"

Some of you may remember a rather long 4 part blog that I wrote in 2015 titled "Antiperspirants & Breast Cancer". As part of that series, I also wrote a blog entitled, "Evaluating Scientific Research", discussing how to evaluate research.

Natural Organic Lavender Essential Oil So how do we determine if the experiment was well designed? Here are a few basic questions to ask:

  • Was the study well designed?
  • Were there enough people in the study to really show any statistical significance?
  • Was there a control group?
  • Were all of the variables considered and how were they controlled?
  • Was there enough information provided to repeat the study and was it repeated?

For me, this case study seemed to lack proper scientific research practices. This is only a partial list of my concerns.

  • The study had a sample pool of only 3 boys. This extremely small sample size can in no way represent the entire population of young males.
  • The case study was not controlled research. There were too many variables involved.
  • The boys were said to have used “some kind of product” that contained lavender or tea tree oils. The study did not even identify the products.
  • Since the entire ingredient list was not supplied, the products may have contained other known endocrine-disrupting ingredients such as artificial fragrances, synthetic ingredients, parabens, or even compounds that leached from the BPA-containing plastic containers.
  • Also if the products are not named, the study cannot be repeated or tested by other researchers.
  • There was no information or investigation of the concentration or purity of the essential oils in any of the products. Essential oils from unreputable sources may be ‘cut’ with artificial chemicals and fillers, which may also be endocrine disruptors.
  • There is no information about the suppliers. Were the essential oils used in these products grown organically? If not, there are known hormone disruptors in many pesticides.
  • I could keep going . . .


Numerous scientists and medical doctors sent letters to the editor of The New England Journal of Medicine concerning the limitations of the Henley study.

Dr. Shirin Kalyan, Ph.D. of the University of British Columbia in Canada wrote:

". . . Given that estrogenic compounds have yet to be detected in either oil, it is important that we carefully interpret these important findings. A growing number of endocrine disrupters in our environment have been shown to accumulate in adipose tissue. Although Henley et al. attempt to show that these oils have estrogenic activity, the results of their reported assays indicate a very weak effect. It would be bewildering if such relatively low hormonal activity alone could instigate prepubertal gynecomastia."

Three medical doctors teaching at universities, Kathi J. Kemper (Wake Forest), Aviva J. Romm (Yale), and Paula Gardiner (Harvard) also sent a letter to The New England Journal of Medicine. In it they wrote:

“The study by Henley et al. raises many questions . . . Did the authors contact manufacturers to report concerns or ask about constituents? The variability, adulteration, and contamination of herbal products have been widely reported, as have discrepancies between labels and contents. Plastic containers may contain phthalates, known endocrine disrupters. What was actually in the products cited in this report?

None of the hormonal testing showed abnormal results, except in Patient 2, who had elevated levels of testosterone (not estrogen). Might the patients' gynecomastia have reflected another pathophysiological process that resolved spontaneously?

Traditional use and clinical trials have not suggested estrogenic effects of tea tree or lavender oil. In vitro testing alone is not adequate grounds for indicting traditionally used products and may raise public fear.”

Robert Tisserand, an international speaker, educator, researcher, and consultant on the science and benefits of essential oils and their safe and effective application, has written numerous articles concerning the claim that Lavender and/or Tea Tree essential oils are hormone disruptors.

"Considering that some 200 tonnes per annum are produced of both lavender oil and tea tree oil, that most of this goes into personal care products, and that very little of the evidence presented for these three cases is convincing, the initial press reports of caution were premature, as are the cautions now found on many websites." Source

He further states

Lavender oil does not mimic estrogen nor does it enhance the body’s own estrogens. It is therefore not a ‘hormone disruptor’, cannot cause breast growth in young boys (or girls of any age), and is safe to use by anyone at risk for estrogen-dependent cancer. The lack of estrogenic action is the conclusion of a new report, which used a novel form of "uterotrophic" assay.

The study cited by Tisserand above, published in the March/April 2013 volume of the International Journal of Toxicology entitled "Uterotrophic Assay of Percutaneous Lavender Oil in Immature Female Rats," showed that lavender had no estrogenic effects, even at concentrations up to 30,000 times higher than the typical exposure from personal care products containing lavender essential oil. This study concluded that, even at these high concentrations, lavender essential oil gave no evidence of estrogenic activity. Source


Although TEA TREE OIL has not yet been tested in vivo (in live people), a report on the Tea Tree Oil by the European Scientific Committee on Consumer Safety stated:

“Since the hormonal active ingredients of Tea Tree Oil were shown not to penetrate the skin, the hypothesized correlation of the finding of 3 cases of gynecomastia to the topical use of Tea Tree Oil is considered implausible.”


Follow-Up Study

At the annual meeting of the Endocrine Society in March 2018, J. Tyler Ramsey presented a new study that suggested lavender, tea tree, and other essential oils could contribute to gynecomastia.

Ramsey did not use case studies like the report from Henley et al, he and colleagues conducted an in vitro study using cancer cells.

The term in vitro refers to a medical study or experiment which is done in the laboratory. Human cells are placed in a test tube or petri dish and exposed to different chemicals, nutrients, or environments, and observed to see how they respond. When this study was evaluated by other researchers there were a number of concerns that came to light that must be taken into account when interpreting these results.

  • An in vitro study that tests cells in a test tube is a long way from demonstrating cause and effect in the human body. Are we expected to assume that these in vitro studies will hold up when completed in the body (in vivo)?

  • The tests are conducted using cancer cells. Are these cancer cells a true representation of the cells in normal breast tissue?

  • The study isolated eight chemical isolates from the hundreds that make up the oils. Does the effect of an individual constituent act the same as when that constituent is part of the whole essential oil? There have been many flawed studies based on that assumption

In his comments about the Ramsey study, Dr. Rod Mitchell, a pediatric endocrinologist at the Queens Medical Research Institute in Edinburgh, said the following:

"The concentration (dose) to which the cells are exposed may not be equivalent to exposure in humans. There is a complex relationship between estrogen, testosterone, and other hormones in the body, that cannot be replicated in these experiments."

"At present, there is insufficient evidence to support the concept that exposure to lavender and tea tree oil-containing products cause gynecomastia in children, and further epidemiological and experimental studies are required."


Essential Oils are Difficult to Study

In March 2018 I wrote a blog titled, “Natural Fragrance Oil? . . . Really?”

In that blog, I discussed the fact that pure essential oils have a complex composition. The chemical profile of one single oil may contain hundreds of individual molecules from a variety of chemical families.

It is difficult to study the exact composition of any one essential oil. The molecular composition of an essential oil will vary from species to species of the same type of plant and even the same species will have variations depending on harvest time, climate, weather, location, and the extraction process.

For example, there are a variety of lavender species used for essential oils in aromatherapy. While the chemical constituents are very similar, they are not the same.

  • True lavender (Lavandula angustifolia)
  • Lavender stoechas (Lavandula stoechas)
  • Spike lavender (Lavandula latifolia)
  • Lavandin (Lavandula x intermedia)

The chemical constituents that make up tea tree and lavender essential oils are found in hundreds of other essential oils, they are not unique to lavender and tea tree.



Small case studies can have value in research, depending on how well they are carried out, how well they are written and whether they are followed up with peer review and more research.

Natural Organic Lavender Essential Oil DropHowever, the Henley case study, as well as the Ramsey study, leave us with too many unanswered questions.

We can all agree that we need further well-designed research.

I believe that all relevant information should be presented so consumers can weigh risks vs benefits and make an educated and informed decision on what is right for them and their families.

However, what bothers me most is that this one report (by Henley et al) has become the "authority bible " for linking lavender and tea tree essential oils to hormone disruption.

If you do some research about this topic on the internet you will see what I mean—almost all information cited stems from this one, single report that is poorly constructed, inconclusive, and mostly anecdotal.


As I said above, the goal of this blog is in no way meant to convince you that essential oils are safe. I simply wanted to share my thoughts and my concerns about the study that began the controversy.

Think for yourself. Be careful who you listen to. Go back and critically read the original research. Do not get caught up in sensationalized headlines.

I hope this blog has provided some information to help you make an informed decision of your own.

Please share your thoughts!


Natural Skin Care Blogs

What Are Essential Oils

What is Aromatherapy?

Why We Use Only Real Plant Essential Oils?

Why Are Synthetic Fragrance Oils So Popular?

How To Do A Simple Allergy Patch Test

The information above pertains to healthy adults. We do not provide information on the safety of essential oils during pregnancy or for use in Children because the available information is often contradictory. If you are interested in using essential oils during pregnancy or with young children please do your own research and be sure to consult your doctor, midwife, or health care professional before use.

The statements regarding health-related benefits of essential oils have not been evaluated by the Food and Drug Administration and are in no way intended and should not be construed as medical advice to diagnose, treat, cure, or prevent any disease or health condition.


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