Almost all cases of chronic cough are caused by allergies, asthma or reflux disease. (BIGSTOCK)

You probably don’t need reminding that cold and flu season is upon us. If, like me, you’ve already had your first bout of one of these nasty bugs, you may be wondering: When will my symptoms go away? Even as my sore throat and stuffy nose have cleared up, my cough has lingered into a second week. It has disrupted my sleep and kept me away from social events.

Two-plus weeks of coughing is quite common in most cases of viral respiratory infections such as mine, says Matthew Mintz, an internist with George Washington Medical Faculty Associates. The average duration of cough, according to a recent study, is 18 days.

If you think that seems like a long time, you’re not alone. A telephone survey by the same researchers found most people expected a cough to last seven to nine days.

That dissonance between how long people expect cough to last and how long it really does sends a lot of people to the doctor. Cough is the most common patient complaint to primary-care physicians and accounts for more than 30 million doctor’s visits annually, according to the Centers for Disease Control and Prevention.

Many people come seeking antibiotics. But if your cough began, as mine did, with a cold and is dry and accompanied by fatigue and muscle aches, then it is most likely related to that cold virus, and antibiotics won’t help clear it up, says Christian Merlo, a Johns Hopkins pulmonologist.

What about over-the-counter cough medicine? Mintz describes two kinds of cough that linger after a cold.

One is a postnasal drip or mucus cough, in which your body’s attack on the cold virus collects in your throat, triggering your cough. Over-the-counter cough and cold medicines can help lessen your symptoms by drying up the mucus and suppressing the cough reflex. But they won’t make it go away completely — or kill the virus that led to it.

The second kind of post-cold cough is called post-inflammatory bronchospasm, and it resembles asthma. “It’s a tightening of the airways that restricts air flow and is accompanied by cough and wheezing,” Mintz says. It’s not asthma, which is a chronic condition, but it’s similar enough that a short course (up to four weeks) of asthma medicines — bronchodilators and/or steroids — can help, he says. You might suspect that this is the problem if it’s worse at night, if you’re wheezing and if you experience shortness of breath, especially during exercise.

Home remedies such as hot water with honey and lemon or taking a hot steamy shower can sometimes help alleviate coughing. But there’s little clinical evidence demonstrating the effectiveness of these approaches. Nor is there much risk in trying. “If it makes you feel better, go for it,” Mintz says.

So when should you worry about cough? If it appears out of the blue and takes hold of you for a couple weeks — and you are not a smoker — or if post-cold coughing continues beyond three or four weeks. Officially, chronic cough is defined as cough lasting for at least eight weeks. In addition to the three problems below, cough can occur with much more serious conditions, such as some cancers and tuberculosis.

More than 90 percent of chronic cough cases are caused by one or more of these three things: allergies, true asthma and reflux disease. After taking a full history and perhaps a lung X-ray, doctors will diagnose the problem step by step.

Merlo says that first he’ll recommend antihistamines, to address allergies and resultant postnasal drip. If there’s no improvement after a week or two, the next step is an inhaler for asthma. If the patient still doesn’t improve, the next step is lifestyle changes and reflux medications such as Prilosec or Nexium. That treatment takes the longest to evaluate — up to six months.

While this three-step plan produces a diagnosis for the vast majority of patients, an unfortunate minority is still left coughing. Many of them have a puzzling condition called chronic cough hypersensitivity syndrome, an overresponsive cough reflex. As its name suggests, the condition causes people to cough more readily than most and in response to triggers that others easily breathe through. Peter Dicpinigaitis, a professor of medicine at the Albert Einstein College of Medicine in New York, who sees many people with the condition, says that “most of my patients have been coughing for more than a year. Or 10 or 20 years” and that there’s little effective treatment beyond prescription antitussives such as codeine, which have unpleasant side effects.

For me, time was the cure. By the time I finished this article, my cough was gone.