California has the second-lowest smoking rate in the nation, but nearly 2.5 million children age 12 and under are exposed to secondhand smoke, researchers say. Lead author Sue Holtby, a senior researcher at the Public Health Institute, and the University of California, Los Angeles, Center for Health Policy Research used data from several cycles of the California Health Interview Survey. The researchers said they estimate 561,000 children are directly exposed to secondhand smoke in the home, while another 1.9 million are at risk because they live in a home where another family member is a smoker, even though smoking may not be allowed in the home itself. Exposure to secondhand smoke puts children at increased risk of developing asthma, respiratory infections and other ailments, Holtby said. Nearly 12.6 percent of African-American children live in homes where smoking is permitted -- three times the rate of any other racial or ethnic group, the study said. Both African-American, at 13.4 percent, and white children, at 12.2 percent, are significantly more likely than other groups to live in a household with an adult or teen smoker, Holtby said.