(The Conversation) – When was the last time you walked into a public space and didn’t hear someone coughing? After three years of flinching at the sound, it can be disarming to hear so many people coughing – and embarrassing if it’s you.
But take heart in knowing that you’re not alone. A long-lasting cough following illness from an upper respiratory infection is surprisingly common. And unfortunately, with the rise in seasonal flu, COVID-19 and respiratory syncytial virus, or RVS cases in the fall of 2022 and winter of 2023, there’s been a lot of coughing lately.
A cough is a common symptom of these sorts of respiratory infections, and coughing is a complaint that leads to an estimated 30 million office visits every year. Some 40% of those end up in a pulmonologist’s office like mine.
Given how ubiquitous persistent coughing is, you might presume that the medical profession has a long list of treatments that we know work. That, unfortunately, depends on why you are coughing. But a cough following an upper respiratory infection does usually go away, in time.
How a cough works
Doctors have long wondered why the duration of cough varies so much following an upper respiratory viral or bacterial infection. The answer likely lies in differences in people, such as the presence of a condition like asthma or chronic bronchitis. I see this same variability in my office: Some patients develop a long-term cough, while others seem to kick the cough much sooner, with no clear explanation.
Coughing occurs due to a complex process that begins with an electrical impulse between the nerves within the airways, including the nose and throat. There are two types of nerves that can trigger a cough in response to external stimuli: chemical receptors and mechanical ones called mechanoreceptors. Chemical receptors respond to smells and fumes; they’re the reason people sometimes cough after breathing in spicy peppers sizzling on a hot skillet. Mechanoreceptors respond to sensations from irritants such as dust.
When these nerves are activated, the throat closes and pressure in the chest increases. This buildup of pressure leads to a burst of air and mucous into the lungs at around 500 mph – a speed nearly twice as fast as the world’s fastest cars.
Studies show that a viral infection alters how sensitive these same nerves are. When you have a viral infection, the resulting inflammatory process produces a molecule called bradykinin that drives the urge to cough. And it’s known that the virus itself can activate genetic changes that increase the sensitivity of these nerve pathways, which leads to more coughing.
But when the acute stage of infection is over and you start to feel better, the body repairs the damages caused by inflammation in your airways and lungs. Through this process, the cough reflex also abates. And the molecular processes that were making you cough and sneeze more frequently settle down and return to a normal state – at least in most cases. Unfortunately, in some people, this process takes longer than in others.
Knowing how long is too long to cough
Doctors find it useful to break respiratory symptoms like cough into specific categories.
There are three main types of coughs: acute, sub-acute and chronic. An acute cough is what most people experience when they’re sick with an active viral infection. A sub-acute cough lingers for three or more weeks following an upper respiratory illness. And a chronic cough is one that persists longer than 12 weeks. Chronic cough is most commonly caused by asthma, postnasal drip and, perhaps surprisingly to some, reflux.
Postinfectious cough is one variety of sub-acute cough and is the lingering cough that many people have after they get over their respiratory infection. It can last for weeks or months and can progress into chronic cough.
Because postinfectious cough is so common, doctors have long worked to determine how many people have a cough that persists after their other symptoms go away. Those estimates vary among studies. One small study in Japan found that of people who have a sub-acute and chronic cough, 12% resulted from a respiratory tract infection.
When it comes to COVID-19, the best evidence to date shows that only 2.5% of the people who have gotten it have also developed a chronic cough after infection. That number may seem small, but it translates to a lot of people coughing, given that the U.S. has more than 280,000 new cases of COVID-19 per week, as of early February 2023. The actual number, though, is unclear because the studies that look at postinfectious cough are often small and only account for the people who got COVID-19 and showed up in their doctor’s office or in a telehealth visit for evaluation.
No simple fix
The American College of Chest Physicians and the European Respiratory Society have published guidelines to help clinicians navigate these uncertainties and the dearth of data available on the diagnosis and treatment of coughing. Although the U.S. guidelines were published in 2006, they still represent the best evidence available for clinicians and their patients.
About half of patients recover from their cough without any treatment. For those who don’t, the limited data available suggests that inhalers, steroids, narcotics and certain over-the-counter medications may provide relief for some people.
In adults, the evidence for the efficacy of various treatments is mixed and limited. In my practice, I often prescribe a non-narcotic cough suppressant called benzonatate, sold under the brand name Tessalon Perles. It works by numbing the nerves in the lungs and airways, calming the cough reflex. Data for treatments in children is equally lacking, and studies have shown that over-the-counter cough suppressants and antihistamines were no more effective than the placebo.
Home remedies can also play an important role for some patients. Many people swear by honey, and there is some limited supporting evidence behind its benefits. One trial showed that honey was more effective at soothing a cough than the placebo over a three-day period.
When in doubt, ask a doctor
Being worried about a persistent cough is understandable – a quick Google search can present plenty of reasons to worry. Though not a very satisfying answer, most coughs really will eventually resolve on their own. However, if you lose weight rapidly, cough up blood, have night sweats or produce lots of sputum, you should talk to your primary care provider. In rare cases, sub-acute and chronic cough can be a sign of lung cancer or various forms of chronic pulmonary disease.
If you are simply nervous about it and want more information and advice, that is reason enough to check in with your doctor. After all, a cough is the reason behind millions of office visits every year.