Julie Mennella and Paul Wise, both of the Monell Center in Philadelphia, said 60 percent of U.S. children ages 3-11 years and 18 million youth ages 12-19 years were exposed to tobacco smoke on a regular basis.
"Cough protects our lungs from potentially damaging environmental threats, such as chemicals and dust. Living with a parent who smokes weakens this reflex, one of the most vital of the human body," Mennella and Wise said in a statement.
The study involved 38 healthy children ages 10-17 who inhaled increasing concentrations of capsaicin -- the burning ingredient in chili peppers and a potent chemical stimulus for cough -- from a nebulizer.
Seventeen of the youth were regularly exposed to smoke in the home, while 21 were never exposed to smoke at home.
The study, published in Tobacco and Nicotine Research, found youth regularly exposed to secondhand smoke required twice as much capsaicin to trigger cough as did non-exposed children -- meaning the exposed children were less sensitive to the irritating environmental stimulus. A similar finding was true for the parents, the study said.
The findings help explain why children of smokers are more likely to develop pneumonia, bronchitis and other diseases and more likely to experiment with smoking during adolescence, the researchers said.