Essential oils do more than make your skin smell good — they also interfere with your hormonal balance, new research has found.

Pre-puberty male gynecomastia (breast tissue growth) is a relatively rare condition. There are numerous underlying conditions that can lead to gynecomastia, however, and in certain cases, doctors can’t pinpoint any immediately apparent cause.

A new study could shed light on the root of such cases: the team found that eight chemical compounds contained in lavender and tea tree oils interfere with hormone levels by promoting estrogen and inhabiting testosterone secretion.

Essential oils are used in the manufacturing of many products such as soaps, lotions, shampoos, or hair-styling products. They’re sometimes mixed in cleaning products, even seeing some use in medicinal treatments, but despite being widely seen as benign, even health-promoting compounds, lead researcher Tyler Ramsey from the National Institute of Environmental Health Sciences says caution is the better part of valor when using such oils.

“Our society deems essential oils as safe. However, they possess a diverse amount of chemicals and should be used with caution because some of these chemicals are potential endocrine disruptors,” he says.

The research was prompted by a growing number of reported cases of gynecomastia associated with an usage or exposure to essential oils. More damning, the symptoms subsided once the patients stopped using the oils, associated products, or otherwise limited exposure to the oils. It was also spurred on by previous findings of co-author Dr. Kenneth Korach, who reported back in 2007 that lavender and tea tree oil would interfere with the activity of male-specific hormones, which could affect the development of boys hitting puberty.

The new study took an in-depth look at eight key chemicals contained in the oils. Four of these were shared in both lavender and tea tree oil, while the other four were found in either oil. To determine the effect of each compound, the team isolated samples of each, and then applied these to human cancer cells in the lab, recording any changes they observed.

All eight compounds showed varying degrees of estrogen promotion, testosterone inhibition, or both. More worryingly, most of these eight compounds are found in some 65 other types of essential oils, Ramsey explains.

“Lavender oil and tea tree oil pose potential environmental health concerns and should be investigated further,” he said.

This hormonal effect could explain why people using essential containing such chemicals run a higher risk of developing breast tissue. Naturally, some individuals will be more sensitive to the effects than others, and the level of use/exposure is also an important factor — so individual mileage may vary. So far, the results do suggest that better regulation or a higher level of consumer awareness are required to limit the negative health impacts of essential oils and products that contain them.

But before you assault an essential oil stand crying bloody vengeance, keep in mind that this study has some significant limitations. Chief among them stand the use of cancer cells and the dosages used. Cancer cells, which is what the team used as a subject, may or may not accurately represent the response of other tissues — say, of healthy breast tissue. The dosages (concentrations) the team used could also not accurately recreate the dosage a living, in-vivo cell might experience.

Living organisms also maintain a complex set of checks and balances on hormonal levels, which a culture of cancer cells in a lab couldn’t replicate.

All these limitations should be addressed by future studies before a definite link between gynecomastia in children and tea tree or lavender oil can be established. Until then, here is a list of safety guidelines on the use of essential oils from the Aromatherapy Trade Council:

• Precautions should be observed when using essential oils since they are highly concentrated.
• Do not apply undiluted essential oils directly to the skin.
• Never use undiluted oils on children under the age of three.
• If you are pregnant you must seek the advice of your doctor, midwife or aromatherapist before using any essential oils.
• When used appropriately, essential oils and aromatherapy products are safe for all the entire family.

The study results will be presented today, 19 March, at the Endocrine Society’s annual meeting in Chicago.

Enjoyed this article? Join 40,000+ subscribers to the ZME Science newsletter. Subscribe now!