-
Now Playing: FDA warns: Don't let your children sink their teeth into benzocaine
-
Now Playing: What is E. Coli?
-
Now Playing: New recommendations for prostate cancer screening
-
Now Playing: Why kids should stay away from sports drinks
-
Now Playing: Weight training can help shape the body and also the mind, studies show
-
Now Playing: Should we be concerned with second-hand pot smoke, especially around children?
-
Now Playing: Could a PG-15 rating be coming to a theater near you?
-
Now Playing: Apple Watch saves teenage girl's life
-
Now Playing: The lowdown on how to keep eggs in your diet while watching your cholesterol levels
-
Now Playing: EpiPen shortage anticipated by FDA
-
Now Playing: Drug could hold cure for baldness
-
Now Playing: What is Ebola?
-
Now Playing: Young American smokers get half of their smoke through hookahs: Study
-
Now Playing: FDA approves preventative treatment for migraines
-
Now Playing: What is cancer?
-
Now Playing: Study shows rear-facing car seats perform well in rear-end crashes
-
Now Playing: Health officials warn of 'nightmare' bacteria
-
Now Playing: What is the definition of twins?
-
Now Playing: Family history of heart disease doesn't mean you shouldn't exercise, study shows
-
Now Playing: Hot off the press: Can peppers cause headaches?