Lavender and tea tree oils found in some shampoos, soaps, and lotions can temporarily leave boys with enlarged breasts in rare cases, apparently by disrupting their hormonal balance, a preliminary study suggests.
While advising parents to consider the possible risk, several hormone specialists emphasized that the problem appears to happen infrequently and clears up when the oils are no longer used. None of those interviewed called for a ban on sales.
The study reported on the condition, gynecomastia, in three boys ages 4, 7, and 10. The problem disappeared when they stopped using skin lotions, hair gel, shampoo, or soap with the natural oils.
It's unclear how often this problem might crop up in other young children.
These plant oils, sometimes called essential oils, are added to many healthcare products, usually for their scent. The oils are sometimes found in other household products or sold in purer forms. Tea tree oil is sometimes used in shampoos for head lice.
The suspected effect in this study is attributed to some chemical within the oils that the body processes like estrogen, the female hormone that promotes breast growth.
The findings are being reported today in The New England Journal of Medicine. The federally funded study came out of the University of Colorado and the environmental health branch of the National Institutes of Health. The findings were first released last year at a science meeting.
The three boys were brought to their doctors with overdeveloped breasts that resembled those of girls in early puberty. They were sore in one case. For each boy, doctors could tie the problem only to their use over several months of the natural-oil products.
The researchers suspected that the oils might be upsetting the boys' hormonal balance. So they did a series of laboratory tests to check how these oils work within human cells. The oils appeared to mimic estrogen and block the male hormone androgen.
On product labels, the oils sometimes are listed by their scientific names: Lavandula angustifolia (lavender oil) and Melaleuca alternifolia (tea tree oil). Such products do not require government approval to be sold unless they make specific health claims.
Dr. Clifford Bloch, a hormone specialist in Greenwood Village, Colo., who treated the three boys, recommended that parents be cautious with such products, especially for prolonged use. "I would not give these products to my children," he said in an interview.
Others sounded less worried. "It takes very little estrogen to cause gynecomastia in a young child," said Dr. Richard Auchus, a hormone specialist at University of Texas Southwestern Medical Center who knew of the study findings. "If they're getting it for a brief period of time, that really shouldn't cause long-term problems."