You may recall the results of a study stating that lavender and tea tree oils caused the development of breast tissue (prepubertal gynecomastia) in three young boys (aged four, seven and ten). This singular study was first published in the New England Journal of Medicine in 2007.¹ All three boys had used skin care products containing lavender and tea tree oils, and were all diagnosed by the same doctor.

If you take a close look at the study, some issues are raised. The solvent used to dilute the oils was dimethyl sulfoxide, which is an estrogen mimicker.² The full list of ingredients in these products were not mentioned, nor the possible chemicals included in the packaging of the products. Parabens were likely included in the ingredients and phthalates in the packaging. In a recent study, diethyl phthalate was found in 103 out of 252 products, which included fragrances, hair care products, deodorants, nail polishes, lotions, skin cleansers and baby products.³ Both phthalates and parabens have been shown to have an estrogenicity presence.^4&5

A number of researchers and doctors have raised some questions regarding the validity of this study. There were three doctors, who made the following comments:

“The study by Henley et al. (Feb. 1 issue)¹ raises many questions. Product names were not provided. Did the authors contact manufacturers to report concerns or ask about constituents? The variability, adulteration, and contamination of herbal products have been widely reported,^2,3 as have discrepancies between labels and contents.⁴ Plastic containers may contain phthalates, known endocrine disrupters.⁵ 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). There was no report on ultrasound examination or needle biopsy, nor were subsequent weight changes reported. 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, though estrogenic effects have been reported for other essential oils and plants. Are occupational exposures to lavender and tea tree associated with estrogenic symptoms? In vitro testing alone is not adequate grounds for indicting traditionally used products and may raise public fear.”

<sub>Kathi J. Kemper, M.D., M.P.H.
Wake Forest University School of Medicine, Winston-Salem, NC 27157
Aviva J. Romm
Yale University School of Medicine, New Haven, CT 06510
Paula Gardiner, M.D., M.P.H.
Harvard Medical School, Boston, MA 02215
1. Henley DV, Lipson N, Korach KS, Bloch CA. Prepubertal gynecomastia linked to lavender and tea tree oils. N Engl J Med 2007;356:479-485
2. Homer LE, Leach DN, Lea D, Slade Lee L, Henry RJ, Baverstock PR. Natural variation in the essential oil content of Melaleuca alternifolia Cheel (Myrtaceae). Biochem Syst Ecol 2000;28:367-382
3. Keane FM, Munn SE, du Vivier AW, Taylor NF, Higgins EM. Analysis of Chinese herbal creams prescribed for dermatological conditions. BMJ 1999;318:563-564
4. Garrard J, Harms S, Eberly LE, Matiak A. Variations in product choices of frequently purchased herbs: caveat emptor. Arch Intern Med 2003;163:2290-229
5. Schettler T. Human exposure to phthalates via consumer products. Int J Androl 2006;29:134-139</sub>

A Canadian doctor also had made some comments regarding the study:

“Henley et al. do a commendable job of sleuthing out the likely cause of prepubertal gynecomastia in the young boys exposed to either lavender or tea tree oil. However, 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.^1,2 A number of such industrial by-products have also been implicated in early thelarche.³ Since these molecules with hormone-modulating activity are fat soluble, topically applied oils may serve as very efficient delivery agents for environmental endocrine disrupters by concentrating them and delivering them into cells. 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.”

Shirin Kalyan, Ph.D.
<sub>University of British Columbia, Vancouver, BC V5Z 1M9, Canada
1. Paris F, Jeandel C, Servant N, Sultan C. Increased serum estrogenic bioactivity in three male newborns with ambiguous genitalia: a potential consequence of prenatal exposure to environmental endocrine disruptors. Environ Res 2006;100:39-43
2. Brevini TA, Zanetto SB, Cillo F. Effects of endocrine disruptors on developmental and reproductive functions. Curr Drug Targets Immune Endocr Metabol Disord 2005;5:1-10
3. Colon I, Caro D, Bourdony CJ, Rosario O. Identification of phthalate esters in the serum of young Puerto Rican girls with premature breast development. Environ Health Perspect 2000;108:895-900</sub>

A later study, completed in Denmark, showed that none of the bioavailable tea tree oil constituents demonstrated estrogenicity.⁶ Bioavailability is the rate, or degree, at which a drug or other substance is absorbed.

Based on the above commentaries and personal experience, I feel that both tea tree and lavender essential oils are safe to use. Many baby care products contain lavender, for its sedative, calming properties. It’s great that essential oils and natural ingredients are being researched, but we shouldn’t be jumping to conclusions after the results of only one study.

Michelle Reynolds, CAHP
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^{1. Prepubertal gynecomastia linked to lavender and tea tree oils. Henley DV, Lipson N, Korach KS, Bloch CA. N Engl J Med. 2007 Feb 1;356(5):479-85. PMID: 17267908 2. Dimethyl sulfoxide is a potent modulator of estrogen receptor isoforms and xenoestrogen biomarker responses in primary culture of salmon hepatocytes. Mortensen AS, Arukwe A. Aquat Toxicol. 2006 Aug 12;79(1):99-103. Epub 2006 Jun 3. PMID: 16828892 3. Phthalates in cosmetic and personal care products: concentrations and possible dermal exposure. Koniecki D, Wang R, Moody RP, Zhu J. Environ Res. 2011 Apr;111(3):329-36. PMID: 21315328 4. Toxic effects of the easily avoidable phthalates and parabens. Crinnion WJ. Altern Med Rev. 2010 Sep;15(3):190-6. PMID: 21155623 5.  Exposure to phthalates: reproductive outcome and children health. A review of epidemiological studies. Jurewicz J, Hanke W. Int J Occup Med Environ Health. 2011 Jun;24(2):115-41. PMID: 21594692 6.  What you see may not always be what you get–bioavailability and extrapolation from in vitro tests. Nielsen JB. Toxicol In Vitro. 2008 Jun;22(4):1038-42. PMID: 18255254}