Passive smoking damages cough reflex in children which is vital for clearing the lungs
Secondhand smoke makes a child's coughing reflex less sensitive
12:03 GMT, 20 August 2012
Secondhand smoke damages a vital cough reflex in otherwise healthy children and teenagers, say researchers.
The study could help explain why children of smokers are more likely to develop pneumonia, bronchitis and other diseases.
Study leader Dr Julie Mennella, from Monell Chemical Senses Center in Philadelphia, said: '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.'
Exposure: Second hand smoke can dull a child's coughing response to irritants
Children are exposed to passive smoking more often than nonsmoking adults, with 60 per cent of U.S. children aged 3-11 years and 18 million youth aged 12-19 years 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 Monell research team conducted the current study to ask if the cough reflex of children and adolescents who are regularly exposed to secondhand smoke is affected in a similar fashion.
In the study, which appears in Tobacco and Nicotine Research, 38 healthy children aged 10-17 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.
Parents also were tested. The amount of capsaicin in the nebulizer was increased after each inhalation until the subject coughed twice. The capsaicin concentration that induced the two coughs was labeled 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.
A similar finding was true for the parents, confirming earlier findings. The findings highlight a previously unrecognized 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.
Study co-author Dr Paul Wise, said: 'This study suggests that even if an exposed child is not coughing, his or her respiratory health may still be affected by secondhand smoke.'
It is also possible that an insensitive cough reflex could increase the risk of teenagers acquiring a smoking habit by making experimentation with smoking less unpleasant.
Future research will explore the relationships among secondhand smoke exposure, cough reflex and the sensory response to cigarettes to ask if exposure-related decreased sensitivity to irritants makes smoking more pleasurable to teens.
The researchers will also seek funding to determine whether impairment of the cough reflex is reversible and how this may relate to the age when secondhand smoke exposure ceases.