The findings by the Monell Centre in Philadelphia, United States, may help to explain why children of smokers are more likely to develop pneumonia, bronchitis and other diseases and also are more likely to experiment with smoking during adolescence.
“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,” said Julie Mennella from Monell who co-directed the study with sensory scientist Paul Wise.
Children are exposed to more secondhand smoke than non-smoking adults, with 60 percent of US children aged three to 11 years and 18-million youth aged between 12 and 19 exposed to tobacco smoke on a regular basis.
Adult smokers are known to have a less sensitive cough reflex relative to non-smokers, meaning that it takes more irritation to elicit a cough in the smokers. The researchers wanted to find out if the cough reflex of children and adolescents who are regularly exposed to secondhand smoke is affected similarly.
In the study, published in the journal Tobacco and Nicotine Research, 38 healthy children aged 10 to 17 years old inhaled increasing concentrations of capsaicin from a nebulizer. Capsaicin is the burning ingredient in chili peppers and a potent chemical stimulus for cough. Seventeen of the youth were regularly exposed to smoke in the home, while 21 were never exposed to smoke at home.
The capsaicin concentration that induced two coughs was labelled as the individual’s cough threshold.
Youth regularly exposed to secondhand smoke required twice as much capsaicin to trigger cough as did non-exposed children, meaning that the exposed children were less sensitive to the irritating environmental stimulus.
The findings highlight a previously unrecognised public health risk from exposure to secondhand smoke. An insensitive cough reflex could make exposed children less able to cope with environmental threats, which could in turn play a role in their increased risk for developing respiratory illness.
“This study suggests that even if an exposed child is not coughing, his or her respiratory health may still be affected by secondhand smoke,” said Wise.
It is also possible that an insensitive cough reflex could increase the risk of adolescents acquiring a smoking habit by making experimentation with smoking less unpleasant.