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Lavender and tea tree oils linked to gynaecomastia

Chemicals in the oils boost oestrogen and inhibit production of testosterone

Mark Gould

Monday, 19 March 2018

New research* adds weight to suggestions that lavender and tea tree oils are linked with gynaecomastia in young boys.

A study presented at the Endocrine Society meeting in Chicago today has found eight chemicals contained in the oils interfere with hormones, boost oestrogen and inhibit testosterone.

The plant-derived oils are found in a number of products such as soaps, lotions, shampoos and hair-styling products. They're also popular as alternative cleaning products and medical treatments.

Lead researcher J. Tyler Ramsey from the National Institute of Environmental Health Sciences (NIEHS), in North Carolina, suggested caution when using the 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."

A growing number of reported cases of male gynaecomastia have coincided with topical exposure to the oils. After they stopped using the products, the symptoms subsided.

A previous study by Dr Kenneth Korach - who was also co-investigator for this study - found that lavender and tea tree oil had properties that competed with or hindered the hormones that control male characteristics, which could affect puberty and growth.

The new study looked at eight key chemicals from the hundreds that make up the oils. Four of the tested chemicals appear in both oils and the others were in either oil. They were tested on human cancer cells in the laboratory to measure the changes. The researchers found all eight demonstrated varying degrees of promoting oestrogen and/or inhibiting testosterone properties.

"Lavender oil and tea tree oil pose potential environmental health concerns and should be investigated further," said Mr Ramsey.

Many of the chemicals tested appear in at least 65 other essential oils, which is of concern, he added.

Professor Ieuan Hughes, emeritus professor of paediatrics at the University of Cambridge told the BBC that the findings "have confirmed why an individual using such oils containing these chemicals may develop breast tissue."

"The anti-male hormone effects are rather unexpected and it is not possible to comment further without the data.

"Of course, not everyone exposing themselves to such oils has adverse effects, so it is possible there are particular individuals who may be more sensitive to the effects of the chemicals, or perhaps are using the products in excess.”

He said attention should be given to better regulation of these products.

Professor Hughes added: "Clearly, the longer-term effects of such exposure are unknown."


*Ramsey TJ, et al. Chemicals in lavender and tea tree oil appear to be hormone disruptors. Presented at ENDO 2018, the Endocrine Society’s 100th annual meeting in Chicago, March 2018.

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