The U.S. Centers for Disease Control and Prevention (CDC) released a report on Tuesday showing that secondhand smoke exposure in the United States has significantly improved by 50 percent between 1999 to 2000 and 2011 to 2012. However, 58 million people are still exposed to it, with the majority demographic being African-American children from low-income communities.

Secondhand smoke exposure was assessed through testing for cotinine, a biomarker of exposure to tobacco smoke which stays in the body for seven to 40 hours upon exposure.

The report highlights that black nonsmokers are more at risk of secondhand smoke compared to whites. Almost half of blacks were exposed to secondhand smoke in 2011 while the rate is only 20 percent for the whites. Income is also a risk, as 43 percent of those in the poverty level have more exposure than 21 percent who aren't.

"Secondhand smoke can kill. Too many Americans, and especially too many American children, are still exposed to it," said CDC Director Tom Frieden, M.D., M.P.H, in a news release. "That 40 percent of children -- including seven in 10 black children -- are still exposed shows how much more we have to do to protect everyone from this preventable health hazard."

The researchers credited the improvement on policies that banned smoking in bars, restaurants and offices.

Further analysis showed that four of 10 children from ages three to 11 are exposed to secondhand smoke, most of whom were exposed at home. That contradicts a 2011 New York Times report that said 83 percent of American households prohibited smoking.

"We've seen a marked decline in secondhand smoke exposure, however, the prevalence still remains alarmingly high and there's also marked disparities," CDC epidemiologist Dr. Brian King told the Wall Street Journal.

Health experts warned that secondhand smoke exposure increases one's risk of dying from heart disease or lung cancer. It can also cause respiratory infections and asthma among children.