I saw this today from the BBC:
Gynaecomastia is rare, and there is often no obvious cause.
But there have been a number of cases linked to use of these essential oils.
The American study found that key chemicals in the oils boost oestrogen and inhibit testosterone.
Not everyone will have the same reaction to an essential oil.
The plant-derived oils are found in a number of products such as soaps, lotions, shampoos and hair-styling products. They're also popular as alternative cleaning products and medical treatments.More:
A previous study by Dr Kenneth Korach - who was also co-investigator for this study - found that lavender and tea tree oil had properties that competed with or hindered the hormones that control male characteristics....Dr Rod Mitchell, honorary consultant paediatric endocrinologist at the Queens Medical Research Institute in Edinburgh said the study "is important in establishing a possible mechanism for the suggested link between gynaecomastia and exposure to lavender and tea tree oils.This was in the BBC story about the older study, which looked at the potential relationship between oils and breasts after several young boys starting developing breast tissue: "The team at the NIEHS carried out tests on human cells and found pure lavender and tea tree oils could mimic the actions of female hormones and inhibit the effects of male hormones, and therefore disrupt the endocrine system in the body."
Child hormone specialist Dr. Clifford Bloch of University of Colorado Denver is quoted in the piece;
"Together, the case histories and NIEHS studies provide support for our hypothesis that topical exposure to lavender and tea tree oils likely caused gynaecomastia in the three patients."
It is not known whether the oils could have similar effects on the endocrine systems of young girls, teenagers or adults.
Note: there are skeptics.