The study, published in the American Journal of Public Health, conducted in 31 countries, found 82 percent of smokers smoke around children.

Concentrations of nicotine in the air were 17 times higher in households with a smoker compared to those without. Air concentrations were 12.9 times higher in households that permitted smoking indoors, compared to those that voluntarily restricted indoor smoking.

Median air nicotine levels in households with smokers were highest in Europe, followed by Latin America and Asia. Nicotine was detected in hair samples in 78 percent of children living with a smoker and 59 percent of those who did not live with a smoker.

"Our research clearly shows that parents are failing to protect their children from secondhand smoke exposure, perhaps because they are unaware of the risks." lead study author Heather Wipfli of The Johns Hopkins Bloomberg School's Institute for Global Tobacco Control said in a statement. "The results highlight the need to improve public awareness of the importance of going outside to smoke to limit the exposure to children living in the home."