Neither traditional use1 nor controlled clinical trials of oral lavender oil2,3 have suggested estrogenic effects.
In one brief report, Henley and colleagues described three cases of otherwise healthy boys with prepubertal gynecomastia, all of whom had normal serum concentrations of endogenous steroids and none of whom were confirmed to have been exposed to exogenous endocrine disruptors .4 The repeated topical application of one or more over-the-counter personal care products that contained lavender oil or lavender and tea tree oils was documented for all three patients. The authors performed in vitro tests that suggested hormonal activities of the oils, which they theorized may have contributed to an imbalance in estrogen and androgen pathway signaling. We are aware of no other reports in the medical literature of gynecomastia or other “estrogenic” symptoms in which lavender oil was assumed to be a factor.
The responses to this case report highlight several limitations. Product names were not provided, and no information was given about constituents of the products.5 Herbal products, and particularly cosmetic products, are widely reported as having a high degree of variability, adulteration, and contamination 6,7 and many supplements fail to meet their own label claims for identity, purity, and potency of ingredients.8 Plastic containers may contain phthalates, which are known endocrine disrupters.9-11 Since these molecules with hormone-modulating activity are fat soluble, topically applied oils may facilitate absorption of environmental endocrine disrupters by concentrating them and delivering them into cells.12 This and other possible causes of gynecomastia in these boys were not examined by the authors of the report.
It should also be noted that none of their hormonal testing showed abnormal results, except in Patient 2, who had elevated levels of testosterone, not estrogen. There was no reporting of ultrasound examination or biopsy results.5 Most critically, the in vitro experiments conducted by Henley and colleagues used concentrations of lavender oil which could not have been obtained from the products as used by the three boys. It is therefore not valid to conclude that lavender oil or tea tree oil caused the estrogenic signs observed in these three cases.
In a clinical trial, topical application of lavender lotion and tea tree oil was specifically investigated for estrogenic effects in women with postmenopausal hot flashes. The products produced no estrogenic effects, and did not affect either FSH levels or hot flashes.13
Estrogenic effects have been reported for other essential oils and plants; some lavender oil constituents could possibly exert such activity at high concentrations. However, the best available evidence suggests that any estrogenic effect of lavender oil, if it exists at all, would be weak. It should go without saying that in vitro testing alone is not adequate grounds for indicting traditionally used products and raising public fear, particularly when superior evidence from clinical trials contradicts those findings.
Lavender oil products for oral use should comply with the most stringent quality standards, such as those set forth in the European Pharmacopoeia.14 When in compliance with or exceeding these standards, and used at the recommended dose, we see no reason to expect any estrogenic effects. The reason the product is not recommended for children is not because of any estrogenic activity, but simply because there are insufficient data available pertaining to this product’s use in children. It is purely precautionary advice. The same can be said for avoiding use in pregnancy and lactation.
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