New Scientist:

Essential oils from plants are touted as having many beneficial properties. But just because they’re natural doesn’t mean they’re harmless – two commonly used plant oils seem to mimic female hormones in the body, occasionally causing boys to grow breasts.

Chemicals from lavender are often used in toiletries for their scent, and are said to aid relaxation. Tea tree oil is a mild antiseptic and a common ingredient of children’s hair products as it is claimed to prevent head lice, although there is little evidence to show it works.

But both of these may have side effects. In 2007, doctors reported three cases of prepubescent boys who had started developing small breasts, despite having the expected hormone levels for their sex and age.

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