A cure for coughing could be in the offing

Often a cough in response to breathing in smoke, carries out a useful purpose in swiftly clearing the airways with a sudden expulsion of air from the lungs. But if the coughing is persistent, and without obvious cause, it can be very stressful. Repeated coughing is said to be the most common cause of visits to the doctor - but until now has largely remained a mystery to science.

According to a study, involving guinea pigs and human volunteers, the problem lies with receptors on nerve endings in the lungs which react to irritants. For victims of persistent coughing in which no useful purpose is being served, the receptors on these nerve endings are repeatedly prompting the cough reflex. The study was launched because of claims that over-the-counter remedies are ineffective, and may be inadvisable for children.

In the research, published in the American Journal of Respiratory and Critical Care Medicine, the scientists show that irritants in the air - including cigarette smoke and air pollution - switch on receptor proteins in lung nerve endings called TRPA1. This in turn causes the cough reflex. When the TRPA1 receptors were blocked in guinea pigs, using drugs, their coughing response to stimulants including a key compound in cigarette smoke was reduced.

Nerves taken from mice, pigs and humans were also used to back up the research, as were reactions by human volunteers. While it would be unwise to permanently prevent coughing - because that would inhibit the ability to clear airways - it seems it may now be possible to work towards preventing unnecessary coughs. For some people, chronic coughing can be annoying and uncomfortable, but for others it can be distressing and can have a severe impact on their quality of life.

Many people say that certain things in the air can make them cough and we are very excited that we have shown, for the first time, exactly what is probably happening inside the lungs. Now that we think we have cracked the mechanism, we can start investigating whether we can stop people from coughing excessively by blocking the receptor protein that triggers it. Most coughs clear up within days, but some have been known to last for months or years. Some have specific causes such as asthma, the common cold, pneumonia or a respiratory infection but experts say around 15 per cent are unexplained.