What experts want you to know about essential oils and breast growth in boys

In an effort to avoid man-made chemicals, many families are now incorporating essential oils, and products that are scented with these oils, into their routines. But new research is confirming that components of these plant-based oils can lead to a surprising, though rare, side effect: Breasts in young boys.

This link was first made in 2007, in a paper published in the New England Journal of Medicine that focused on three boys between the ages of four and 10 who had prepubertal gynecomastia, a rare hormonal condition that causes breast glands to grow in boys. All three of the boys regularly used personal care products containing lavender essential oil and/or tea tree oil, and when they stopped using the products, their bodies returned to normal. Since then, several other similar cases have been reported.

Earlier this month, these stories made headlines again when the National Institute of Environmental Health Sciences (NIEHS) shared the results of a study due to be published later this year that confirmed lavender and tea tree oil can disrupt the body’s endocrine (hormone) system. The study’s lead investigator, J. Tyler Ramsey, a post-baccalaureate research fellow at the NIEHS, explains that the study involved a series of test tube experiments with eight chemicals found not only in lavender and tea tree essential oils but in at least 65 other essential oils. The experiments showed that these chemicals can, in fact, set the stage for the development of prepubertal gynecomastia. But they didn’t investigate if the selected compounds could lead to other hormone-related issues in boys and girls.

Though the findings might sound frightening, the researchers say there’s no need to purge your home of lavender or tea tree oil products. “All we’ve done in this study is identify that there are components in lavender and tea tree oil that have hormonal activity,” says Kenneth Korach, senior principal investigator with the NIEHS’s Receptor Biology Group and a co-investigator on the NIEHS study. “If your child is being bathed in lavender or tea tree oil and they aren’t showing any abnormalities, then there’s no reason to be concerned,” he says.

“Millions of people use lavender and tea tree oil but it’s only this small sub-group of patients that have been identified [as],” says Korach. Exactly why only a very small number of boys who frequently use either or both of those substances develop gynecomastia is unknown. Korach says that further research is needed to identify what makes some boys’ hormonal systems sensitive to lavender and tea tree oil.

One thing the NIEHS study does is highlight just how little we know about these substances. Essential oils are concentrated, plant-derived liquids obtained through mechanical methods such as distillation or cold pressing. While they have been used for thousands of years, surprisingly little research has been done on their impact on the human body. “A lot of society thinks that because the oils are natural, they’re safe,” says Ramsey.

But as his research shows, essential oils do have the potential to impact the body’s endocrine system and lead to physical changes. Whether they could be related to other hormone-related conditions is unknown. “It’s a field that should be more investigated because there are so many people that use them,” says Ramsey.

So what are parents to do while we await the research? Dan Metzger, a paediatric endocrinologist at the BC Children’s Hospital, recommends practicing moderation. “Most of these things are probably not harmful in small doses.”

He notes that, since the 2007 research first linked prepubertal gynecomastia to lavender and tea tree oil, paediatric endocrinologists have asked parents of boys with the condition if their sons use products that contain the oils. Metzger does not believe rates of prepubertal gynecomastia have increased, and he’s not overly concerned about the impact either substance could have on a child’s endocrine system—in part because, when essential oils are used as ingredients in personal care products, they’re generally used sparingly. “It’s a tiny, tiny drop of lavender that’s need to make a product smelly,” he says, explaining that most kids aren’t likely to be exposed to high doses.

To minimize potential harm from essential oils, Metzger warns parents to never feed them to their children or apply them directly to their skin. “Be mindful that just because something’s natural doesn’t mean that it’s completely safe,” he says.

If you suspect your son might be developing gynecomastia, “the possibility that lavender or tea tree might be the source of the problem should at least be considered,” says Korach. Check the ingredient lists on any personal care products and tell your healthcare practitioner if he’s exposed to lavender or tea tree oil.

Read more: 6 things to know about melatonin for kids Top 10 natural cure-alls for families