Increased estrogen levels can cause gynecomastia (the development of breasts) in men. Bodybuilders who take anabolic steroids are well aware of this problem because some of the testosterone is converted to estrogen. Researchers from the National Institute of Environmental
Health Science in North Carolina found that oils contained in common products such as shampoo, hair gels and lotions can also stimulate the estrogen receptors and cause breast tissue growth.
The scientists learned about this accidentally after examining several young boys with gynecomastia, but normal estrogen levels. The boys had been using products containing lavender or tea tree oil, both of which have estrogen- like effects. Breast size in the boys decreased when they stopped using the products. Many substances found in the environment can alter estrogen and androgen metabolism, which could affect training gains in bodybuilders. We'11 have a lot to learn about this topic.