Researchers say lavender oil and tea tree oil may contain endocrine-disrupting chemicals that cause abnormal breast growth in young boys.

Lavender oil may be soothing on the senses, but exposure to it as well as tea tree oil has again been prospectively linked to abnormal breast growth in young boys.

The condition, known as prepubertal gynecomastia, involves the enlargement of breast tissue.

Researchers have found that chemicals in the oils, which are derived from plants, can cause disruptions to the endocrine system.

The research was presented at the recent Endocrine Society’s ENDO 2018 conference in Chicago. It hasn’t yet been published in a peer review journal.

“Specific chemicals in lavender and tea tree oil possess estrogenic and anti-androgenic properties,” J. Tyler Ramsey, the lead researcher and post-baccalaureate research fellow at the National Institute of Environmental Health Sciences (NIEHS), told Healthline.

His team looked at eight chemicals in both oils to measure their activity.

Ramsey explained that not all of the chemicals studied showed estrogenic and anti-androgenic properties. But some showed “much stronger effects” than others while some chemicals did not affect the body at all.

“This shows that there are specific chemicals in lavender and tea tree oil that contain endocrine-disrupting chemicals [EDCs] and are hormonally active,” he said.

Ramsey said his research differs from a 2007 study that only looked at the oils and not the components in them. Those researchers suspected that topically using over-the-counter products containing the oils on a repeated basis was the cause of gynecomastia in three patients studied.

Ramsey said they did not look at the results of oil use compared to application methods, such as applying the oils topically versus diffusing them in water.

“We only measured the potential activities of the eight selected components,” he noted.

Multiple clinical cases of gynecomastia have been linked to topical exposure in boys before they reach the age of puberty, Ramsey added.

Ramsey said parents should be concerned about the findings, although more research is needed to fully understand the oils’ role as EDCs.

“Parents should be aware of these findings and potential risks when deciding to use lavender and tea tree oil, as they do contain EDCs,” he said.

Dani Stringer, MSN, CPNP, PMHS, a pediatric nurse practitioner from Arizona, agreed that parents should know about the possible harms of essential oil. She generally discourages parents from using essential oils on children.

“Too often I encounter patients that wrongly consider essential oils to be natural and therefore automatically believe that they are safe. This is not the case,” Stringer told Healthline. “The high concentration found in essential oils can definitely impact the body and this is seen even more in children. Now we are discovering the hormonal impact they can have as well.”

Stringer sees children with allergies and asthma that are triggered by diffusing oils.

“This can have very serious implications on children,” she added.

Because essential oils are not FDA-regulated, it’s difficult to know the concentrations of chemicals in them.

“Concentration can vary greatly from brand to brand,” Stringer said.

In addition to topical uses, inhaling the oils by diffusion are commonly used. Those effects were not studied in Ramsey’s research. Essential oils should never be ingested.

Stringer said that diffusing essential oils — many parents choose lavender to help with sleep — in a young child’s room could “certainly be harmful.”

Robert Tisserand, an essential oil educator, said that diffusing is not harmful.

He said there is “no concern” for using essential oils, as in vitro studies are “notoriously problematic in terms of extrapolating to real-world use by humans.”

Tisserand contends that the plastic trays used in the 2007 study contained estrogenic and anti-androgenic phthalates and bisphenol-A.

“We know from other research that essential oils leach these substances out of plastic,” he told Healthline.

That explains why Ramsey’s research found hormonal effects in the oils, Tisserand added.

Ramsey said that both essential oils “pose potential environmental health concerns and should be investigated further.”