New research suggests that the chemicals contained in essential oils such as lavender oil and tea tree oil may disrupt the normal functioning of hormones, leading to a condition called male gynecomastia in prepubescent boys.

Male gynecomastia is a condition in which boys develop noticeable breasts as a result of having abnormally high levels of estrogen, the female sex hormone.

Research has previously linked the condition to essential oils, such as lavender and tea tree oil.

Such oils are regularly used in personal hygiene and cosmetic products, as well as in laundry detergents and aromatherapy candles and devices.

An older study from 2007 found that gynecomastia coincided with the use of essential oil-based products, and that the symptoms of the condition disappeared when these products were no longer used.

Not only that, but the same study then investigated human cell lines and also found that lavender and tea tree oils had estrogen-boosting and anti-androgenic effects.

A new study—which was presented at ENDO 2018, the annual meeting of the Endocrine Society, held in Chicago, IL—now strengthens the link between these essential oils and gynecomastia.

Researchers led by J. Tyler Ramsey—of the National Institute of Environmental Health Sciences—tested the impact of eight components that are commonly found in tea tree and lavender oil on human cancer cells to study their effect on hormonal activity.

The results suggest that the chemicals are endocrine disruptors—that is, substances that disturb the normal activity of hormones in the body.

In the past, researchers have exposed a wide range of endocrine-disrupting chemicals in common products, such as toothpaste, sunscreen, and lip balm, which prompted campaigners to urge an official ban on these products.

Lavender, tea tree oil as endocrine disruptors

Essential oils contain hundreds of chemicals. For the new study, however, Ramsey and team picked out and analyzed:

• eucalyptol
• 4-terpineol
• dipentene/limonene
• alpha-terpineol
• linalyl acetate
• linalool
• alpha-terpinene
• gamma-terpinene

The first four components are common to both tea tree oil and lavender oil. The research revealed that all of the chemicals tested had an endocrine-disrupting activity to a certain extent.

While some of the compounds had little to no estrogenic or testosterone-inhibiting activity, the changes that were caused by the essential oils appeared to coincide with those present in gynecomastia.

"Lavender oil and tea tree oil," explains Ramsey, "pose potential environmental health concerns and should be investigated further," especially since many of the chemicals they tested can be found in 65 other essential oils that are currently marketed as safe.

The public should now be made aware of the potential risks of using essential oils, urge the study authors, suggesting that the Food and Drug Administration may wish to regulate these products in the future.

"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."

J. Tyler Ramsey