“The results of our laboratory studies confirm that pure lavender and tea tree oils can mimic the actions of estrogens and inhibit the effects of androgens,” said Korach. “This combinatorial activity makes them somewhat unique as endocrine disruptors.”
The referenced study: http://www.nejm.org/doi/full/10.1056/nejmoa064725
Abstract:
"Most cases of male prepubertal gynecomastia are classified as idiopathic. We investigated possible causes of gynecomastia in three prepubertal boys who were otherwise healthy and had normal serum concentrations of endogenous steroids. In all three boys, gynecomastia coincided with the topical application of products that contained lavender and tea tree oils. Gynecomastia resolved in each patient shortly after the use of products containing these oils was discontinued. Furthermore, studies in human cell lines indicated that the two oils had estrogenic and antiandrogenic activities. We conclude that repeated topical exposure to lavender and tea tree oils probably caused prepubertal gynecomastia in these boys."
Note: I ask as I use Colgate Total myself and if harm >> benefits at the concentration levels found in toothpaste, then I have a vested interest in discontinuing its use. A doctor might advise a patient who has a genetic risk of heart disease to take small quantities of aspirin, just as a dentist might advise someone with a gingivitis risk to use triclosan-containing toothpaste -- in both cases, a determination of benefit:harm must be evaluated.