"A lot of young people think they're invincible, but the truth is young people are knuckleheads," she laughed, pointing out that they often cut themselves while cooking or injure themselves by dancing on bar stools.
Obama added that thanks to Obamacare, coverage for young people was much cheaper.
"Now young people can get insurance for as little as $50 a month, less than the cost of gym shoes," she explained.
Fallon pointed out that the website healthcare.gov was actually "up and running."
The First Lady joined a skit with comedian Will Ferrell and Jimmy Fallon, who played two awkward girls hosting a talk show called "Ew!"
Obama explained to the two "girls" that it was important to keep moving, and the program quickly evolved into a dance party.
She also explained that potato chips were "ew" and encouraged them to eat kale chips instead, because they were high in Omega-3 fatty acids.