Secondhand smoke, a recognized health hazard, still afflicts one in four nonsmokers in America, says a report released by the Centers for Disease Control and Prevention.

Most worrying is its effect on children; the CDC says two in five children between the ages of 3 and 11 are still being exposed to chemicals in secondhand smoke linked to Sudden Infant Death Syndrome, asthma and respiratory and ear infections.

Secondhand smoke is responsible for the death of more than 400 infants annually, as well as around 41,000 adult nonsmokers, the CDC reports.

"Secondhand smoke can kill. Too many Americans, and especially too many American children, are still exposed to it," says CDC Director Dr. Tom Frieden.

There has been progress -- overall exposure to secondhand smoke in the United States has been reduced by half between 1999 and 2012 -- but risks still remain, he says.

"[The fact] that 40 percent of children -- including 7 in 10 black children -- are still exposed shows how much more we have to do to protect everyone from this preventable health hazard," he says.

The CDC assessed the level of secondhand smoke exposure using measurements of blood levels of cotinine -- a chemical compound created in the body from the nicotine found in tobacco -- from data gathered by the National Health and Nutrition Examination Survey.

Secondhand smoke can contain as many as 7,000 different chemicals, of which 70 have been identified by researchers as causing cancer.

"There is no safe level of exposure," the CDC says.

Almost 700 U.S. cities, along with 26 states and the District of Columbia, have passed measures banning smoking in restaurants, bars and in workplaces.

The primary source of secondhand smoke encountered by nonsmokers is in the home where someone in the family is a smoker.

In addition, one in four Americans lives in multi-unit housing and faces unwanted smoke emanating from other units or in common areas where smoking is allowed.

"Although we've made significant progress in reducing smoking rates ... some populations are subjected to the deadly impact of tobacco more than others," says Chris Hansen, president of the American Cancer Society Cancer Action Network.

He notes that secondhand smoke disproportionately impacts Hispanics, African-Americans and Native Americans, who are more likely to be employed in industries -- including service, hospitality and manufacturing industries -- that offer minimal levels of protection from smoking.