Now Playing: Young American smokers get half of their smoke through hookahs: Study

Now Playing: Ohio teacher to donate kidney to 10-year-old girl

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: Guys' guide to getting in shape for a wedding

Now Playing: First lady Melania Trump undergoes kidney surgery at Walter Reed

Now Playing: What is Ebola?

Now Playing: Women may not be getting enough information about heart disease, AHA warns

Now Playing: Inside the #GainingWeightIsCool fitness trend

Now Playing: Consumer Reports ranks the best sunscreens ahead of summer

Now Playing: 29 states now affected by E.coli romaine lettuce outbreak: CDC

Now Playing: Weight training can help shape the body and also the mind, studies show

Now Playing: New recommendations for prostate cancer screening

Now Playing: Try this mother-daughter workout for Mother's Day

Now Playing: Firm with ties to Russian oligarch allegedly made payments to Trump's attorney, says adult film star's lawyer

Now Playing: Why kids should stay away from sports drinks

Now Playing: Mom and 2 daughters lose more than 150 pounds

Now Playing: This son saved his mom's life with an organ donation

Now Playing: Teen wakes up after being declared brain dead

Now Playing: Miraculous recovery for 13-year-old declared brain dead