According to national data from 2003 to 2010, half of all children ages 6 to 19, even those with asthma, have been exposed to secondhand smoke.
For kids ages 6 to 11, even low levels of second hand smoke were linked to more missed school days, trouble sleeping, less physical activity and more wheezing, the authors write in Academic Pediatrics.
The fact that kids with asthma are still inhaling others' smoke is a real problem, said Dr. Karen M. Wilson, who studies children's' exposure to secondhand smoke at Children's Hospital Colorado in Aurora.
"Secondhand smoke consists of particulate matter, and chemicals, both of which induce an inflammatory response in the airways, which can cause an asthma attack," said Wilson, who was not involved in the study.
Limiting physical activity is also dangerous because it increases the chances a child will become obese, which worsens asthma, she told Reuters Health.
For older children, secondhand smoke was not linked to those negative symptoms.
Image: Asthmatic child with a smoker, via Shutterstock