Wise parents should keep their children out of any environment where smoking is allowed, even if no one is smoking there at the time. The reason? Growing concern about the potential harms caused by exposure to the nicotine and other tobacco toxicants in thirdhand smoke that linger in the environment long after the smoke is gone.

“Our findings indicate that children carry tobacco smoke toxicants on their hands, even when nobody around them is smoking,” Dr. E. Melinda Mahabee-Gittens and colleagues at the University of Cincinnati wrote recently in Tobacco Control, a BMJ journal.

Noting that the residue from secondhand smoke “accumulates in dust, in objects, on home surfaces and on smokers’ skin and clothes,” the researchers said that these environmental tobacco toxicants are easily transferred from children’s hands to their mouths and bodies.

Children, and especially infants, face a greater risk than adults of developing complications from thirdhand smoke because they spend more time indoors surrounded by objects contaminated with tobacco toxicants.

The Cincinnati researchers found evidence of high levels of nicotine on the hands of 25 young children when one or both parents smoked. The children had been taken to the emergency room with an illness potentially related to exposure to the remnants of tobacco smoke. Children exposed to both thirdhand smoke where they live and play and secondhand smoke from people who smoke around them experience a double whammy, they pointed out.

Furthermore, the team said, thirdhand smoke may be even more of a hazard than secondhand smoke because it contains “novel pollutants not found in secondhand smoke, has multiple exposure routes and has a much longer duration of exposure.”

Another new study from the University of Cincinnati of 7,389 nonsmoking adolescents that was published in Pediatrics found that those who lived with a smoker and had thirdhand smoke exposure at home were more likely to be short of breath and have a harder time exercising than their peers. They were also prone to wheezing during or after exercise and to having a dry cough at night.