When a person smokes, those immediately around that person are forced to "smoke" also. If people around the smoker have asthma, the smoke can make their condition worse.
For children especially, being around secondhand smoke has been linked to greater risks of ear infections, pneumonia, asthma and worse lung function.
Yet a recent study found that children with asthma were still exposed to about the same levels of secondhand smoke in 2010 as they were in 1999.
Meanwhile, improvements were seen among children's exposure if they did not have asthma.
This study, led by Kenneth B. Quinto, MD, MPH, of the National Center for Health Statistics at the US Centers for Disease Control and Prevention (CDC), looked at how many kids were exposed to secondhand smoke in the US from 1999 to 2010.
The researchers used data from the National Health and Nutrition Examination Surveys for the years 1999 to 2010.
These surveys gather data from interviews and physical examinations of approximately 5,000 people each year across the US.
The people included represent all ages, socioeconomic groups and races/ethnicities of those across the US. The precise number of children included in each year's survey was not available, but the info is used to estimate percentages for children across the US.
Children's exposure to secondhand smoke was measured based on the amount of a certain chemical in their blood that is a product of tobacco smoke.
Among the children who did not have asthma, the percentage of those exposed to secondhand smoke decreased from 57.3 percent in 1999 to 44.2 percent in 2010.
However, among children with asthma, there was only a tiny decline: 57.9 percent of kids with asthma were exposed to secondhand smoke in 1999-2002, and 54 percent were in 2007-2010.
This decline was so small that, overall, the researchers concluded there was no significant change in the rate of children with asthma exposed to secondhand smoke.
During the years 2007 to 2010, a higher percentage of children with asthma were exposed to secondhand smoke (54 percent) than those without asthma (44.2 percent).
The researchers also identified several characteristics that made it more likely that children with asthma would be exposed to secondhand smoke.
Girls were more likely than boys, and Mexican-American children were more likely than other races/ethnicities, to be exposed to secondhand smoke if they had asthma.
Children aged 6 to 11 who had asthma were at the highest risk for being exposed to secondhand smoke.
In addition, children from the lowest income levels (a family income below 350 percent of the federal poverty guidelines) were more likely than children in other socioeconomic groups to be exposed to secondhand smoke while suffering from asthma.
The authors noted that asthma is common among children: about one in ten children have asthma in the US.
"This is truly disheartening news – while children without asthma have seen a reduction in secondhand smoke exposure, asthmatic children (a group known to have deleterious effects from second hand smoke) have unfortunately not seen a reduction," said Dr. John Oppenheimer, a physician at Pulmonary and Allergy Associates.
"Of further concern is that asthmatic children as a whole are more likely to have second hand smoke exposure," Dr. John Oppenheimer told dailyRx News. "It is obvious that we still have much work before us with regard to the education of parents of asthmatics."
The authors noted that the National Asthma Education and Prevention Program Guidelines for Diagnosis and Management of Asthma recommend that people with asthma avoid tobacco smoke exposure.
This study was published August 8 by the National Center for Health Statistics at the CDC.
The research was funded by the CDC. All authors are employed at the CDC and did not report any disclosures.