tea tree deodorant

Tea Tree Oil Side Effects: Unsafe For Kids, Men, Dogs & Cats

[toc]Whole Foods has really stepped up their game when it comes to natural personal care products.

Sure, they’ve always stocked brands like Tom’s of Maine (owned by Colgate). Though now, you will find fluoride free toothpaste from even the obscure independent Ayurvedic brands. Along with mouthwash, deodorant, shampoo, and even chew sticks to quit smoking.

But when it comes to these natural personal hygiene products, it’s hard to ignore how many are using tea tree oil these days.

During a recent stroll through the aisles, we lost count as to the number which proudly touted it as the starring ingredient.

Ironically, many of them were marketed towards men.

Men’s deodorants, body washes, shampoo, conditioner, and more.

Online, you will see many flea and itch relief pet sprays that highlight the oil as the active ingredient.

Even though there’s good science demonstrating tea tree oil benefits for rosacea and other skin conditions, it has a dark side. Especially for males and children. Even for dogs and cats, it’s a risky choice.

Likewise for lavender essential oil, which shares many of the same chemical constituents. Given its scent, lavender is more common in female-oriented products.

Is there estrogen in tea tree oil?

There is not actual estrogen in tea tree oil. However, there are plant-based molecules similar in structure. Known as phytoestrogens, they can bind to human hormone receptors. This can have biological effects similar to real estrogen. There are case reports suggesting the essential oil causes gynecomastia, better known as man boobs, and poses possible reproductive side effects.

The first major alarm bell

One of the first reputable sources to bring up the danger of tea tree oil was a 2007 study published in the prestigious New England Journal of Medicine.

Researchers from the National Institutes of Health (NIH), in collaboration with the University of Colorado at Denver, suspected a link after diagnosing three young boys with gynecomastia.

The three Caucasians were 4, 7, and 10 years old. All were confirmed to have healthy, normal hormonal levels. Their testosterone, estrogen, and others were all in-line.

Yet, one thing they had in common is that all of these kids were being given lavender oil and/or tea tree oil soaps, lotions, shampoo, and other personal hygiene products.

While this could just be circumstantial, after the products were discontinued, the side effect of male breast tissue growth and puffy nipples subsided or went away entirely.

When these scientists put the essential oils to the test in the lab, to see if they may be hormone disruptors, their findings were quite startling:

“The results of our laboratory studies confirm that pure lavender and tea tree oils can mimic the actions of estrogens and inhibit the effects of androgens. This combinatorial activity makes them somewhat unique as endocrine disruptors.”

In other words, not only do they mimic estrogen, but they also suppress testosterone. A double whammy.

Since a picture is worth a thousand words, just take a gander at these graphs from the study…

graphs showing tea tree oil estrogen side effects in lab experiments

These graphs show the estrogenic (estrogen-mimicking) effect of the plant oils on cultured human breast cancer cells (MCF-7 cell line). Shockingly, even a 0.025% concentration of tea tree essential oil has about the same effect as estradiol, which is the real human estrogen hormone.

graphs of testosterone lowering effects of lavender oil as seen in study

Does tea tree and lavender oil lower testosterone?

Yes. The anti-androgenic activity of them was pitted against flutamide, a chemotherapy medication used for lowering testosterone levels during prostate cancer treatment. As evidenced by cultured human cells, the testosterone-lowering effect was similar with tea tree and lavender oils.

You would think that with such a discovery coming from reputable source, personal care product manufacturers would be wary of using these oils.


Consumers – blissfully ignorant – think it’s good for them. As such, they keep buying tea tree oil shampoo, skin care, mouthwash, etc.

Rather than do the right thing and drop the ingredient, manufacturers keep ramping up their usage of these oils. Because hey, that’s what people want and it’s selling products! (1) (2)

The 2018 ENDO study

As presented at the Endocrine Society’s 100th annual meeting in Chicago, a new study further cemented the case that both tea tree and lavender oil are dangerous to kids. Specifically young boys, because of gynecomastia risk.

“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.”

That’s a quote by the lead investigator, J. Tyler Ramsey. He comes from the National Institute of Environmental Health Sciences (NIEHS), which is part of the US government’s NIH.

While there are hundreds of different compounds in these essential oils, they presented data on specific chemicals which are in a high concentration:

  • Eucalyptol
  • 4-terpineol
  • Dipentene/limonene
  • Alpha-terpineol

Those chemicals are found in both lavender and tea tree essential oil.

They also presented data on the following four, which are found in one oil or the other; linalool, linalyl acetate, alpha-terpinene, and gamma-terpinene.

As shown in lab studies using human breast cancer cells, these compounds – even in trivial amounts – influenced the cells in a way which is similar to the hormonal influences that cause breast tissue growth in male teens (prepubertal gynecomastia).

Even though the focus was tea tree and lavender, they noted that these compounds are found in nearly 70 other common essential oils! (3)

The implied side effects

While the research in recent years has been focused on gynecomastia, the potential repercussions of these compounds extend far beyond just that issue.

Side effects of tea tree oil may include increased estrogenic activity and decreased testosterone expression in both males and females. For men, this can result in breast tissue growth, decreased libido, and lower muscle mass. In women, this can cause tenderness and fibrocystic lump formation in breasts, decreased sex drive, irregular periods, bloating, mood swings, and headaches. In teen and prepubescent girls, exposure may lead to menstruation beginning at a younger age than normal.

Nearly 80% of breast cancers are what’s called ER-positive. Meaning, they grow in response to estrogen. Too much estrogen can trigger or accelerate tumor formation. That means lavender, tea tree, and other essential oils may increase breast cancer risk if ingested or absorbed through the skin. (4) (5) (6)

In short, males and females need both of these sex hormones, but it’s about having them in the right ratios. Too much or too little of one, or both, can lead to dangerous health conditions.

Just as with humans, using tea tree oil in dogs’ ears and on their skin for fleas is dangerous. Mammals, which include cats, all have molecularly identical sex hormones. As such, phytoestrogens which influence human hormone receptors will have a similar effect in those of dogs and cats. For that reason, you may want to avoid using them on pets.

Putting the risk into perspective

For once, your products being “watered down” may be a good thing.

The truth is that many hand soaps, body washes, shampoos, lotions, and deodorants add minuscule amounts of hot ingredients, simply so they can promote them on the packaging.

The actual amount of the ingredient that’s used may not be much.

Of course, given how hot tea tree oil has become, even a little bit in a lot of your skin care products can cumulatively add up to a high amount of exposure.

Jason healthy mouthwash tarter control cinnamon clove

The other factor to consider is where they are making contact with your body.

Those making direct contact with a mucous membrane, such as inside your mouth, will likely result in more absorption than something like a shampoo, which makes momentary skin contact and is then largely washed off.

In addition to tea tree oil toothpaste and mouth rinse, your arm pits are known to be more absorbent than some other areas of skin.

Just as many people fixate on BPA while ignoring bigger dangers, the same can happen with this issue.

Sure, uses of tea tree and lavender warrant caution no doubt, but dairy milk and cheese contain actual estrogen. Yes, organic milk included. Remember, milk is meant to spur the growth of the baby calf; it’s naturally chock-full of hormones! (7) (8) (9)

If you’re going to dump your tea tree deodorant and toothpaste, it’s hypocritical to turn a blind eye to your love of cheese. Perhaps you even have a casomorphin addiction.