Lavender and tea tree oils can cause gynecomastia.
Preliminary evidence suggests that lavender and tea tree oils might cause gynecomastia in young boys.
These enlarged breasts are very rare before puberty, so an endocrinologist became alarmed when three preteen boys got them.
It turns out they were all using a shampoo, hair gel, or soap that contained lavender...or lavender plus tea tree oil. The gynecomastia got better when the boys stopped using the products.