It hurts, makes a loud rattling noise, and travels at up to 60 miles an hour. Over the next few months, it will be responsible for more than two million visits to GPs, and more than £500m will be spent on medicines this year trying to stop it. The cough is one of Britain's biggest health problems. In a full year, the costs to the economy are now estimated to have reached £1bn.
While in some cases it can be a symptom of more serious underlying diseases or problems from asthma to cancer, or a side effect of a drug, a consequence of smoking, or a tic, in most cases it is the result of the common cold or flu.
And cough medicines are the main remedies. The problem for sufferers is that there is a bewildering choice, including suppressants, expectorants, decongestants, antihistamines and codeine, as well as alternative remedies.
But do they work? Is the money well spent? "Experts say much of it is wasted money," says a report from Harvard University. "According to American College of Chest Physicians guidelines, many of the active ingredients in over-the-counter cough remedies are ineffective. You'd be better off taking an early generation antihistamine and a nasal decongestant.''
"There is some debate as to whether cough medicines work,'' says NHS Direct. "They usually contain only small amounts of the active ingredients. But they do appear to work for some people.
''Much of any impact they do have may also be down to the placebo effect: "In clinical trials on cough medicines, up to 85 per cent of the reduction in coughs is associated with the placebo treatment and the active pharmacological component of the medicine only contributes 15 per cent of the reduction,'' says a report from Professor Ron Eccles of the Common Cold Centre at Cardiff University.
Sweet cough syrups
According to research at Cardiff University, 58 out of the 60 over-the-counter sweet cough syrups contain a sweetener such as sucrose, glucose, honey, or treacle, and may woork through their sweet taste and the plaacebo effect.
"The review proposes that the major bene-fit of cough medicines for treatment of coughs associated with common cold is rellated to the placebo effect rather than the pharmacological effect of an active ingredient,'' says Professor Eccles. The report says the sweet or in some cases bitter taste of a medicine may trigger salivation and the secretion of mucus. "Placebo-controlled clinical trials have discredited most tra-ditional cough medicines as they have ussually concluded that the cough medicine is little more effective than a matched placebo medicine.''
These medicines work by affecting the production and clearance of mucus, and help bring up phlegm so that coughing is easier.
Some studies show they are effective, whhile othershave found no or little effect: "If you want a free, reliable way of loosening mucus, just try drinking plenty of water the next time you have a cold,'' says the Harvard Unniversity report.
They act on the brain to hold back the cough refflex, and are usually used for dry coughs.
According to new American College of Chest Physicians guidelines, they may have limited effect incoughs caused by colds. "There is no clinical evi-encede that over-the-counter cough expectorants or suppressants relieve coughs," says Dr Richard Irwin of the University of Massachusetts Medical School, who led the team that drew up the guidelines.
Designed to work by constricting blood vessels, which shrinks swollen membranes and allows more air to pass through the nose.
"Decongestants can be wonderfully effective in the short run but they also present problems. You can become dependent on nose drops which contain oxymetazoline,'' says the Harvard report.
These drugs work in hay fever by blocking histamine, but in coughs and colds the older types of antihistamines like brompheniramine and chlorpheni-ramine have another effect - making you sleepy and inhibiting coughs.
The American College of Chest Physicians guidelines advise adults with acute coughs to use an older variety of antihistamine combined with a decongestant. "There is considerable evidence that older type antihistamines help to reduce coughs."
It's a traditional remedy for cold and coughs, and includes onions, sweet potato, carrots, celery and parsley as well as poultry.
Folklore says it works, and so too do researchers at the University of Nebraska. They found that it acts as an anti-inflammatory, and it speeds up the discharge of mucus to ease the symptoms of coughs and colds. Just what does it is not clear, but it may be the combination of ingredients.
Essential oils containing menthol and eucalyptus have been used for centuries for treating coughs and colds. Menthol works as a mild anaesthetic and is used to relieve sore throats. It also makes the mouth and throat feel cooler.
"Menthol provides relief from nasal congestion by causing a cool sensation in the nose and also relieves the symptoms of sore throats andcoughs by a local anaesthetic action. It may also help to inhibit infection of the airway,'' according to the Cardiff Common Cold Centre.
Oscillococcinum, a medicine made from the heart and liver of the duck, is said to be effective in treating flu symptoms.
"A clinical trial on the treatment of influenza-like symptoms demonstrated superiority of the homeopathic medicine oscillococcinum over placebo,'' the Cardiff Common Cold Centre reports.
A daisy-like purple flower, it is a traditional native American treatment for coughs, colds and sore throats. It is now one of the bestselling herbal remedies in the UK, with sales of £30m predicted for this year.
Some research suggests it is little better than placebo, while other work shows beneficial effects. According to the Cardiff Common Cold Centre: "There is some scientific evidence which indicates that echinacea does affect our immune system by stimulating the activity of white blood cells. Lozenges containing echinacea may help prevent infection by boosting the immune system and could in theory abort a common cold infection and prevent the development of symptoms.''
A standard ingredient in cough remedies, it works as a mild narcotic. A University of Manchester study suggests it may be no more effective than placebo at treating coughs. Researchers who studied patients with chronic lung disease found that after the placebo treatment the patients' coughing fell from an average of 8.27 seconds an hour to 7.22 seconds, and after codeine to 6.41 seconds. "Although there was a significant reduction after codeine, from a statistical standpoint there was really no difference between codeine and placebo - despite the fact that the dose of codeine used far exceeds that in over-the-counter cough remedies."
An ingredient in chocolate could help stop persistent coughs. Researchers have discovered that theobromine suppresses vagus nerve activity involved in causing coughing.
According to research at Imperial College, theobromine is nearly a third more effective in stopping persistent coughs compared to codeine: "Not only did theobromine prove more effective than codeine, at the doses used it was found to have none of the side effects. Normally the effectiveness of any treatment is limited by the dosage you can give someone. With theobromine having no demonstrated side effects in this study it may be possible to give far bigger doses, further increasing its effectiveness,'' says Professor Maria Belvisi.
Widely used as a traditional remedy, it is a thicker syrup said to ease the symptoms of coughs, especially in children. Research at the University of Beirut shows that the oil reduces cough symptoms more than a placebo, but the difference was not statistically significant: "Sesame oil did not result in marked improvement in cough symptoms.''
Works by making secretions looser and easier to cough up. Can be done with the head-over-a-bowl-approach, or by adding moisture to air with a steam vaporiser or cool-mist humidifier.
According to Dundee University: "Inhalations with steam help. Boil some water, pour it into a basin, drape a towel over your head, inhale the steam for four or five minutes, several times a day (be careful not to scald your nose). Frequent hot drinks also help."
So what should you take?
The Harvard University report concludes: "For your everyday cough from a common cold, the new guidelines advise taking one of the allergy medicines that combine an older antihistamine and a decongestant. The only older antihistamine that is specifically recommended is brompheniramine, but it's not unreasonable to try products that contain other older antihistamines, like diphenhydramine or chlorpheniramine. The guidelines also say that naproxen might be helpful. But these are just guidelines. If you think a product is working fine, it probably won't hurt you, although you may be paying for a placebo effect rather than a proven remedy."
Professor Eccles adds: "I think the analgesics aspirin, paracetamol and ibuprofen are the first line in treating colds and flu."
Coughing: the facts
More than £500m is spent in the UK every year on over-the-counter medicines for coughs and colds.
The cost of acute cough to the UK economy is estimated to be at least £979m.
A cough can travel at up to 60mph.
A cough can be a symptom of many ill-nesses including asthma, bronchitis, colds, flu, smoking, some medicines including ACE-inhibitors used for heart failure, and whooping cough. It can also be a symptom of serious conditions, including lung cancer.
Different types of cough
A dry cough occurs when the throat is inflamed, but no phlegm is produced.
A chesty cough is usually when phlegm is produced, often as a result of an infection.
Acute coughs last less than three weeks and account for more GP visits than any other complaint.
Chronic coughs last eight weeks plus, are more common in females and the obese, and account for one in 10 hospital referrals.
25 per cent of chronic cough cases cannot be attributed to a specific cause.
What happens when we cough?
Our bodies sense there is something in the airway, and without thinking, we breathe in and inflate the lungs.
The glottis, the top of the windpipe, is briefly closed.
Contraction of muscles generates high pressure of air from the lungs against the closed glottis.
When the pressure has built up, the glottis automatically opens, and pressurised air explodes out, forcing out any debris along with it.