Causes of Gynecomastia: Lavender and Tea Tree Oil?

The story has been kicking around the Internet so long it has the feel of an urban legend: lavender and tea tree oil can cause gynecomastia. Our patients and people online ask from time to time – is it true?

The answer to this question from our perspective is, “It’s not yet clear.” There is some evidence that lavender and tea tree oil may contribute to gynecomastia, particularly in young males, but the proof is far from conclusive. Here’s the story.

It all started early in 2007 when the New England Journal of Medicine published a study by a University of Colorado pediatric endocrinologist. The physician found enlarged breasts in three of his male prepubescent patients and discovered that each had used personal products like lotion containing lavender, tea tree oil or a combination. In addition, after the boys discontinued the use of such products, the gynecomastia disappeared.

A researcher at the National Institute of Environmental Health Services, or NIEHS, then tested the essential oils. He found that the substances mimic the action of estrogen, which stimulates breast tissue growth, and/or inhibit androgen, which governs male attributes and limits breast development. The NIEHS researcher said that the combination of effects made the essential oils “somewhat unique as endocrine disruptors” (see https://www.nih.gov/news-events/news-releases/lavender-tea-tree-oils-may-cause-breast-growth-boys).

All this may sound convincing, and if you’re concerned about enlarged male breasts in adolescents it is something to consider – to a point. There are several factors to weigh when deciding how worried to be about lavender and tea tree oils. First is the small size of the study – just three boys. Much larger groups would have to be studied, including control groups, for the findings to be notable.

Also, the boys used different personal care products, most not identified in the study, containing unknown concentrations of these essential oils. In addition, there are many other endocrine disruptors the boys may have also been exposed to, such as ingredients found in pesticides.

Scientists have spoken up since 2007 to point out the shortcomings of the lavender and tea tree oil study. And even while stating that the case histories of the boys and the tests on the oils showed “an association” between the substances and gynecomastia, the NIEHS itself said the strength of the association remained unknown and called for further research.

To our knowledge no further studies have yet been published. So here we stay for the time being: there may be a link between the use tea tree oil and lavender in and gynecomastia in boys. When you think about it, when it comes to shampoos and lotions, there are plenty of choices these days. The best answer we can give now is “better safe than sorry.”