A new showed that both lavender and tea tree oils may result in abnormal breast growth, or gynecomastia, in boys by causing an imbalance in estrogen and androgen pathway signaling.

Prepubertal gynecomastia is uncommon and idiopathic in over 90% of cases. It's often found in children as part of a routine physical exam.

In the February 1st issue of the New England Journal of Medicine, Henley and colleagues from the University of Colorado report on 3 children whose gynecomastia resolved after stopping the use of lavender and tea tree oils.

Both oils were tested on breast cancer cell lines to determine their interaction with the estrogen and androgen signaling pathways.

The first boy (age 4) presenting with worsening gynecomastia was found to have a normal testicular examination and hormonal profile. His gynecomastia resolved after his mother stopped applying a "healing balm" to the skin containing lavender oil.

Another 10 year old boy presented with a 5 month history of gynecomastia and a normal evaluation. The areolar mounds disappeared 9 months after discontinuing the use of a hair styling gel containing Lavandula angustifolia (lavender) oil and Melaleuca alternifolia (tea tree) oil.

The third boy age 7 years was evaluated for a 1 month history of gynecomastia and was found to be using lavender scented soap. His gynecomastia resolved several months after stopping the use of the soap.

The authors exposed 2 human breast cancer cell lines (MCF-7 and MDA-kb2) to both lavender and tea tree oils and measured estrogen-receptor dependent estrogenic activity.

Both oils were found to modulate the expression of estrogen-regulated genes c-myc, ctsd, and IFGBP3 in a manner similar to 17beta-estradiol administration. By adding dihydrotestosterone to the cell media, the authors also showed that both oils possessed in vitro antiandrogenic activity in the same magnitude as adding flutamide to the medium.

Although little is known about the effect of these oils in adults, an inquiry regarding their use is warranted in all patients presenting with gynecomastia or decreased libido. 

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