A cold weather cough that will not clear up could be the first sign of more serious illness, say experts.
Pharmacists have been asked by their professional body to pick out people with persistent problems and urge them to see their GP.
A long-lasting cough could indicate chronic obstructive pulmonary disease, which affects millions in the UK, or even cancer.
Specialists said catching illness early would improve treatment chances.
At this time of year, millions of people develop chest problems, many caused by infections, which will clear up over the following days or weeks.
However, the Royal Pharmaceutical Society of Great Britain said that a few may be early symptoms of lung cancer.
They said that a cough that lasts more than a few weeks, coupled with breathlessness, or fatigue, deserves the attention of a GP rather than just more cough medicine.
Graham Phillips, a member of the society's board, said: "Many people will repeatedly buy cough medicines or maybe iron tablets for tiredness and a lack of energy.
"If you can't seem to shake off symptoms that seem similar to colds and flu, such as a persistent cough or chest infection, or if you keep losing your voice, feel breathless or tired and lacking in energy, then ask your pharmacist for advice instead of buying an over-the-counter medicine or picking something up in the supermarket."
Lung cancer is difficult to treat in many cases because by the time symptoms become obvious it is well advanced.
Only one in 10 of more than 30,000 people who develop it each year is alive after five years.
A survey by the Roy Castle Lung Cancer Foundation found that only a third of people questioned associated a cough with lung cancer, and only 11% said that a persistent cough would be a worry.
Dr Jesme Fox, the charity's medical director, said he hoped that the joint campaign would increase early detection, and save lives.
The British Lung Foundation agreed that a persistent cough deserved a GP appointment, but said there were other, more likely explanations than cancer.
Dame Helena Shovelton, its chief executive, said: "A persistent cough can be an early sign of lung cancer but it can also be an early symptom of other lung diseases such as chronic obstructive pulmonary disease (COPD) which includes chronic bronchitis.
"Our research has shown that nearly 3.5 million people in the UK are at a high risk of having lung conditions such as COPD and 28% of smokers would think their cough was just a 'smoker's cough'.
"We would urge anyone with symptoms such as nasty cough, wheezy chest or breathlessness to ask their GP for a lung function test or to take our online breath test.
"The earlier people are diagnosed with lung cancer or other lung conditions the better their chances of getting treated successfully."