About 25 percent of nonsmokers in the US—or 58 million people—are still inhaling secondhand cigarette smoke, according to a February 2015 CDC report. Exposure was determined by blood tests for cotinine, a biomarker for nicotine.The number is an improvement from previous figures, which stood at 53 percent as recently as 2000. Smoking has been banned in many public places since then, and the smoking rate has declined. Blacks, children, and people with low income are most likely to be exposed to secondhand smoke.
According to the CDC, secondhand smoke also causes about 34,000 premature deaths from coronary heart disease in American nonsmokers each year, along with 7,300 deaths from lung cancer.
Another reason to avoid secondhand smoke: It increases the risk of stroke in nonsmokers, suggested a national study in the American Journal of Preventive Medicine in December 2015. Nearly one-quarter of the 22,000 participants reported being exposed to tobacco smoke at least one hour a week. They were found to be about 30 percent more likely to have a stroke over a six-year period than people not exposed to smoke, after adjustment for other stroke risk factors.
Originally published April 2015. Updated December 2015.
See also: Thirdhand Smoke: A Lingering Threat.