A federally funded study conducted by the University of Colorado finds certain oils found in some shampoos can cause young boys to develop enlarged breasts.
The study, conducted by CU and the National Institutes of Health, appears in the New England Journal of Medicine.
Researchers say lavender and tea tree oils found in some shampoos, lotions and soaps can disrupt boys' hormonal balance in some rare cases. The condition clears up when affected boys stop using the natural oils.
Doctor Clifford Bloch, a hormone specialist in Greenwood Village, Colorado, treated three boys for the condition and recommends that parents be cautious with such products, especially with prolonged use.