There’s a bit of a monster pesticide-resistant lice epidemic going around New York City, it seems like every school near us is infested. Last week, a third of my younger daughter’s class had lice. We didn’t.
Besides regular comb outs and wearing their hair up or in braids, we’ve been applying aromatic oils to our daughters’ heads before school. The mix of oils was recommended by a friend:
- Tea tree, lemongrass & lavender in apricot kernel oil (25% dilution)
- Put a couple of drops on your hands, rub palms together & then pat it on the hair.
- Avoid contact with skin
- Definitely avoid contact with eyes!
I mentioned the oils to some other parents and emailed it to the class. This morning the classroom smelled like tea tree oil.
But one parent mentioned some concern about estrogenic qualities of lavender and tea tree oils. This was troubling me so I did some research.
From what I found, the concern about tea tree and lavender originated with this 2007 observational study published in The New England Journal of Medicine (NEJM):
Prepubertal Gynecomastia Linked to Lavender and Tea Tree Oils
NEJM received several critical letters about the study which should be read too.
This was foremost an observational study, and the author’s conclusions seem loosely drawn from the results of three cases. (Gynecomastia is enlarged breasts in males) From their abstract:
We investigated possible causes of gynecomastia in three prepubertal boys who were otherwise healthy and had normal serum concentrations of endogenous steroids. In all three boys, gynecomastia coincided with the topical application of products that contained lavender and tea tree oils. Gynecomastia resolved in each patient shortly after the use of products containing these oils was discontinued.
First issue with the study is that not all three cases were exposed to tea tree and lavender, here’s what they mention in the text:
- patient 1: “healing balm” containing lavender oil
- patient 2: regular use of styling gel and shampoo containing tea tree and lavender oils
- patient 3: lavender scented soap and occasional lavender lotions
Only one of the three of their observed subjects even recorded contact with tea tree oil.
As pointed out in the letters, there’s virtually no mention of dietary factors. Soy is known to have estrogenic effects and processed soy products are in everything these days.
Experiments using breast cancer cells to measure estrogenic effects seem to only vaguely apply to gene-expression in boys.
Both oils stimulate ERE-dependent luciferase activity in a dose-dependent manner, with the maximum activity observed at 0.025% volume per volume (vol/vol) for each oil, corresponding to approximately 50% of the activity elicited by 1 nM 17β-estradiol. Treatment with higher doses of the oils was cytotoxic.
The most extreme numbers were collected at the maximum possible oil dose before the cells they were treating were poisoned so much they died. I have no idea what that dosing would be to a human, but I suspect there’d be significant physical reaction before getting to that point.
Presenting their findings as “Average fold increase above control” without the actual numbers can be suspect. An increase from 0.02 to 0.06 is a three-fold increase, but still relatively insignificant.
Also, the delivery vehicle used in testing, dimethylsulfoxide, is suspected of having estrogenic effects:
Our data show that DMSO-induced significant increase in ERα, ERβ, Vtg and Zr-protein genes in a time-dependent manner. Indirect ELISA analysis showed a time-specific effect of DMSO. The use of DMSO as carrier solvent in fish endocrine disruption studies should be re-evaluated.
Most tea tree oil studies in PubMed seem to be related to its anti-fungal qualities or efficacy as a delivery vehicle for topical medications. I did find one study which looked at transdermal absorption of tea tree oil and found that very little passes through the skin:
…only a small quantity of TTO components, 1.1–1.9% and 2–4% of the applied amount following application of a 20% TTO solution and pure TTO, respectively, penetrated into or through human epidermis.
I believe this study looking at the effects of dietary soy proteins on tumor growth demonstrates greater estrogenic effects of dietary soy protein isolate than the tea tree oil study showed with direct in vitro exposure.