Zunika Crenshaw cringes as a tire swing whips her children around in circles just a little too fast. It's a sunny afternoon in the park, in Pleasanton, Calif. As her children play, she keeps a close watch on their breathing.
She says asthma is in her genes.
"You have a family, a person who has four kids, and all of them have it, including me," she says. "And then my mom has it, and my sister's two kids."
A little girl, 3-year-old Jhase, runs over to her, wheezing. Crenshaw grabs an inhaler, and her daughter breathes deeply from it.