Jan. 31, 2007 -- Repeated use of products containing lavender oil or tea tree oil may spur breast growth in prepubertal boys, experts report in The New England Journal of Medicine.

The effects fade when boys stop using the products, note the researchers.

"This report raises an issue of concern, since lavender and tea tree oil are sold over the counter in their 'pure' form and are present in an increasing number of commercial products, including shampoos, hair gels, soaps, and body lotions," write researchers Derek Henley, PhD, and others.

Henley works at the National Institute of Environmental Health Sciences (NIEHS), which is part of the National Institutes of Health (NIH).

"We want to encourage doctors who may be seeing patients with gynecomastia to ask their patients about the products they are using," says Henley's colleague, Kenneth Korach, PhD, in a NIEHS news release.

"Patients with prepubertal gynecomastia may want to consider reducing the use of products that contain these oils," says Korach.