Lavender and tea tree essential oils 'make male breasts develop'

A suspected link between abnormal breast growth in young boys and the use of lavender and tea tree oils has been given new weight, after a study found eight chemicals contained in the oils interfere with hormones.

As BBC reports, gynaecomastia is rare, and there is often no obvious cause.

But there have been a number of cases linked to use of these essential oils.

The American study found that key chemicals in the oils boost oestrogen and inhibit testosterone.

Not everyone will have the same reaction to an essential oil.

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.

The study results will be presented on 19 March at the Endocrine Society's annual meeting in Chicago.

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