Many personal hygiene products now contain tea tree oil. Is there any evidence that it has curative powers? —B.J.M., Jacksonville, Texas

Only a little, and it’s not impressive. Test-tube studies suggest that tea tree oil kills some bacteria and fungi. A few small human studies have found that various concentrations of it helped reduce mild acne, athlete’s foot, and toenail fungus. But more research is needed to establish those benefits. Even if the oil works, you’d have to apply it daily for a month and a half (for acne) to six months (for toenail fungus). Don’t drink tea tree oil; that may cause confusion, disorientation, and even coma.

Read our Natural Medicine Ratings for tea tree oil (subscribers only).