A new study has found that more than 50 percent of non-smokers in New York have elevated levels of cotinine in their blood, which means that they were recently exposed to toxic second-hand smoke in concentrations high enough to leave residues in the body.
The residue is cotinine, a by-product of nicotine breakdown, which is not harmful itself but signals exposure to environmental tobacco smoke.
A Health Department study has shown that 57 percent of adult New Yorkers (2.5 million) have elevated cotinine levels, compared to 45 percent of adults nationwide - a finding that may reflect the city's dense, urban character.
Second-hand smoke contains many harmful chemicals, which can cause cancer and heart disease in adults, as well as serious health problems for children.
The data come from the New York City Health and Nutrition Examination Survey, which was conducted in 2004, one year after New York City's smoke-free air law took effect.
Although the law protects non-smokers from the dangers of second-hand smoke at work and in some public places, this study shows that many non-smokers are not fully protected.
The study, therefore, suggests that creating a smoke-free home is the most important step that New Yorkers can take to protect their families.
"Tobacco smoke is a toxic pollutant," said Dr. Thomas R. Frieden, New York City Health Commissioner.
"Most New York City non-smokers are breathing in dangerous chemicals in second-hand smoke, potentially increasing the risk of cancer and heart disease.
"Households with a smoker should set a 'no smoking' policy at home to protect the family. We encourage all New Yorkers who smoke to quit - this is the best way to protect yourself and others," he added.
This is the first time researchers have used blood tests to gauge second-hand smoke exposure in New York City, so it is not possible to say whether cotinine levels have increased or decreased over time.
The study has been published online this week in the journal Nicotine and Tobacco Research.