Essential oils are pretty much everywhere right now—people are using them to treat acne, cure cold sores, and even lose weight.
But a scary new study, presented Saturday at The Endocrine Society’s 100th annual meeting and expo, shows that lavender and tea tree oils may contain chemicals linked to abnormal breast growth in young boys. Huh?!
This isn't exactly new: A 2007 study published in The New England Journal of Medicine also found that repeated use of lavender and tea tree oil products could cause male gynecomastia (a.k.a breast growth.)
Researchers had also previously determined that lavender and tea tree oil have oestrogen-like properties (the hormone responsible for the development and regulation of the female reproductive system), as well as testosterone-inhibiting properties (the hormone responsible for the equivalent in males).
That's problematic because anything that screws with your hormones—also known as an endocrine disruptor—can cause major problems down the line.
“They can mimic the hormones in our body or interfere with normal processes and cause tumour growth, developmental, reproductive, and immune issues,” says women's health expert Jennifer Wider.
Yeah, not cool.
So, in this new study, the researchers decided to take a hard look at exactly which chemicals in lavender and tea tree oil were to blame. They found that eight components were particularly suspect: eucalyptol, 4-terpineol, dipentene/limonene, alpha-terpineol, linalyl acetate, linalool, alpha-terpinene, and gamma-terpinene.
In lab tests on cancer cells, they found that all of these chemicals impact estrogen and testosterone in the body in one way or another.
Even freakier: Many of the chemicals that the researchers tested also appear in at least 65 other essential oils.
The fact that essential oils contain chemicals that mimic oestrogen should be particularly concerning to women, says Wider. “[Estrogen-like chemicals] can potentially cause early puberty and growth of breast cells,” she says.
This doesn’t mean you’re totally screwed if you use these products — more studies are needed, Wider says. But, she adds, it's worth paying close attention to this issue going forward.
This article originally appeared on Women's Health US