A study published in the New England Journal of Medicine found that two commonly used aromatherapy essential oils have been linked with temporary breast enlargement in young boys, a condition known medically as prepubertal gynecomastia.
A pediatric endocrinologist at the University of Colorado at Denver diagnosed three boys, aged four, seven, and ten years, with prepubertal gynecomastia.
All had regularly used either soap, skin lotions, shampoos or styling products containing tea tree oil and lavender oil. One boy used a skin balm with lavender oil, another used a hair gel and shampoo with lavender and tea tree oil, and the third used lavender soap and lavender-scented skin lotion. Breast size returned to normal after these products were discontinued.
After researchers at the National Institutes of Health learned about these cases, they conducted experiments using human breast cells to see if these essential oils could influence hormones. They report that tests showed both oils may boost estrogen, the female hormone that stimulates breast growth, and inihibit androgens, the hormones that inhibits breast tissue growth.
The researchers said it is possible that the boys' breast growth may have stemmed from other causes.
It is unknown whether the oils could have similar effects in prepubertal girls, adolescents or adults.
Several hormone experts have advised parents to consider the possible risk, but emphasized that it appears to occur infrequently and return to normal when the oils are discontinued.
Lavender is widely used in natural hair and skin products. The scent is thought to help people relax.
Tea tree oil has been shown to have antimicrobial properties and is commonly found in natural shampoos and soaps.
It is not known whether chemicals found in soap, shampoo and skin lotions may have had an effect.
The National Institute of Environmental Health Sciences (NIEHS). Lavender and Tea Tree Oils May Cause Breast Growth in Boys
Henley D, Lipson N, Korach K, Bloch C. Prepubertal Gynecomastia Linked to Lavender and Tea Tree Oils. "New England Journal of Medicine", Feb. 1, 2007.