Lavender oils found in soaps, shampoo and laundry detergent may cause abnormal breast development in boys and girls as young as three, a new study has suggested.
Previous research has linked abnormal breast growth in young boys to these essential oils, but the latest study is the first to look at the connection in girls.
It found that those with premature thelarche - when breasts develop prematurely in girls before the age of eight with no other signs of puberty - saw their symptoms disappear after they stopped using lavender oil products.
Lavender oil, the most popular essential oil for men and women in the US, is known for its calming qualities.
The girls studied were exposed to lavender perfume, bath soap and a teacher’s lavender oil-scented sticks.
One boy with pubertal gynaecomastia, abnormal breast growth in boys, was also studied. He was exposed daily to a lavender oil cologne and noticed his breast enlargement aged four.
The US study said the children noticed their breast tissue return to a normal level when they stayed away from lavender products.
Lead investigator Jeffrey Ramsey, a research fellow at the US government’s National Institute of Environmental Health Sciences (NIEHS) said: “It appears that essential oil products have the potential to cause premature breast growth in young girls and boys, so it may be best to discontinue using them on children.”
Until now, research has exclusively looked at how essential oils could affect breast tissue growth in boys by affecting their hormones levels.
A study published in The New England Journal of Medicine in 2007 found that three healthy pre-pubertal boys had larger breasts after using products containing lavender or tea tree oils. Symptoms went away when they stopped using the products.
A NIEHS research team, including Mr Ramsey, suggested in 2018 that essential oils can affect oestrogen and testosterone levels in the body.
As well as looking at case studies, the latest research tested whether components in these essential oils can interfere with hormones.
It found that lavender oil and tea tree oil can mimic oestrogen and block testosterone.
According to the study, the essential oils have “greater potency as anti-androgens than as oestrogens” which is “more relevant to blocking the natural action in boys than girls, where androgens inhibit breast development”.
It is still possible that symptoms disappeared naturally and it was a coincidence the children stopped using such oils at the same time.
The researchers do not recommend “avoidance of these products”, but rather that they “should be considered in the evaluation of premature breast development in girls and gynaecomastia in boys and adult men”.