A suspected link between abnormal breast growth in young boys and the use of essential oils has been found by American researchers.
A study group from the National Institute of Environmental Health Science (NIEHS) found that eight chemicals contained in the lavender and tea tree oils interfere with human hormones.
Those key chemicals in the oils boost oestrogen and inhibit testosterone, which can finally lead to the gynecomastia.
The plant-derived oils are found in a number of products such as soaps, lotions, shampoos and hair-styling products. They are also popular as alternative cleaning products and medical treatments.
The leading researcher in the NIEHS, J. Tyler Ramsey, suggested caution when using these oil-contained products.
"Our society deems essential oils are 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 said.
A growing number of reported cases of gynecomastia have coincided with topical exposure to the oils.
In these reports, the symptoms subsided after people stopped using the products.