Lavender and other fragrant oils may cause breast growth in boys. Pediatric endocrinologist Clifford Bloch of the University of Colorado at Denver diagnosed three otherwise healthy boys—ages four, seven and 10— with prepubertal gynecomastia, a rare condition that leads to breast growth in prepubescent males. They all had used lavender-scented soap and skin lotions, or shampoos or styling products that contained lavender oil and tea tree oil. The gynecomastia subsided several months after the boys stopped using the products. Bloch's colleagues at the National Institute of Environmental Health Sciences tested the oils in gene expression studies on lab-grown human breast cancer cells and found that they could mimic estrogens, the primary female sex hormones, and inhibit androgens, the primary male sex hormones. Whether the oils have similar effects on prepubescent girls, adolescents or adults is unknown. The researchers report their findings in the February 1 New England Journal of Medicine.