I posted a summary of this on the You Grow Girl forums. The July 1 issue of Science News carried an article about the newly-discovered feminizing effects of lavender and tea tree oil in young boys, and appear to be responsible for a rise in breast development in pre-pubescent boys. The article is on the Science News website, but is available only to subscribers of the print magazine, so I'll summarize the findings here.
The story: Ever since 1990, Dr. Clifford Bloch, an endocrinologist in the Denver area, had been seeing a number of cases of gynecomastia in pre-pubescent boys. Gynecomastia, or breast development in boys, is unusual, and when it occurs it's usually the result of some hormonal problem. However, testing the boys for sex hormones showed a normal ratio of the various sex hormones, so it wasn't a hormone production problem. After a great deal of laborious detective work, trying to find out what these boys all had in common, the doctor traced down two possible culprits: lavender essence and tea tree oil. All the boys had been using soaps, hair gel, shampoo, and similar topical products with these two herbal ingredients. In some cases, boys had been putting pure lavender oil on their skin. When Bloch suggested they stop using these products, the condition disappeared within a few months.
But a simple correlation doesn't prove a cause, so the doctor contacted a health sciences research lab in North Carolina, and asked them to investigate. The researchers carried out an in-vitro experiment, treating human breast tissue cultures with lavender or tea tree oil. In both cases, the oils caused the cells to turn on estrogen-regulated genes and turn off androgen-regulated genes. In other words, both act as estrogen mimics, turning on genes normally controlled by estrogen, such as genes that stimulate breast tissue growth. It also turns off genes controlled by male hormones.
While Bloch's observations were on young boys, the same effect may also happen in young girls. In fact some health researchers have noted a recent rise in pre-pubescent breast development in girls. With the increased popularity of lavender as a calming aroma in aromatherapy, more people are using lavender-scented products, and users include children in the household.
The article had no report as to whether spammers will soon be pushing breast enlargement products featuring lavender and tea tree oil. It probably wouldn't work, either. Kids have such low levels of sex hormones that the small amounts of estrogen mimics in these oils may be upsetting the balance, but adults may not even notice the difference. However, women with or recovering from estrogen-related breast cancer will also want to take note of this article, and discuss it with their doctor.
Moral of the story: enjoy lavender and tea tree oil now and then, but don't overdo it. And for pity's sake, don't let your kids slather lavender oil all over themselves. Even without the hormonal problem, it's a bit much.