The story here is that three young boys in Colorado aged four, seven and 10 were diagnosed with enlarged breast tissue, a rare condition called prepubertal gynecomastia. Their physician, a pediatric endocrinologist at the University of Colorado, looked for common environmental exposures and discovered that all three had used either lavender-scented soap and skin lotions or shampoos or styling products that contained tea tree oil or lavender oil.
To investigate whether the oils were responsible, researchers at the National Institute of Environmental Health Sciences (NIEHS) conducted laboratory tests to see if lavender and tea tree oils mimicked the effects of estrogen or blocked the effects of androgen, the male hormone that inhibits breast tissue growth. They also tested the ability of the oils to influence gene expression.
Tests showed that pure lavender and tea tree oils had dual effects: they acted like estrogen, and also blocked androgen effects. Their combined impact makes them "somewhat unique as endocrine disruptors," the researchers said. Fortunately, the oils didn't upset the boys' natural circulating estrogens and androgens, and a few months after the three stopped using the soaps, lotions and shampoos, their breasts returned to normal. The study was reported in the February 1, 2007 issue of the New England Journal of Medicine.
What does this mean? Maybe nothing. Case reports of just three individuals are suggestive, at best, and the test tube results may have no clinical significance. We do not know what caused the abnormal breast development in these boys. Interestingly, one of the three boys had a fraternal twin who had used the same products as his brother but did not develop enlarged breasts.
Lavender has been used for centuries in topical products without being associated with any toxicity, and tea tree oil also has a long history of safe use. I would not expose young children to high doses of any essential oils, but for now, I see no reason to avoid moderate use of soaps or shampoos containing them.
Andrew Weil, M.D.