There's a paradox here: As recently as the 1980s, asthma was underdiagnosed and undertreated, and in impoverished urban areas it still is, killing 3,630 people in the United States in 2013. Yet the prevalence of asthma more than doubled from the 1980s to the mid-1990s, and has stayed around a historical high of 8.3 percent of children and 7 percent of adults. Trouble is, the wrong people are being told they have asthma, Drs. Andrew Bush and Louise Fleming of Imperial College, London, write in the Archives of Disease in Childhood, which commissioned their analysis.

So-called cough variant asthma, whose only symptom is a chronic cough, is especially likely to be overdiagnosed. A 2007 study found that children with persistent coughs rarely have the airway inflammation and narrowing that defines asthma and causes wheezing, coughing, or shortness of breath. Even wheezing is not a surefire symptom. Wheezing "means that airways are narrowed," Bush said, "but that can be caused by mucus" from a cold, not necessarily asthma. (In adults, wheezing can signal congestive heart failure or chronic obstructive pulmonary disorder.)

One reason for concern about overdiagnosing asthma is that inhaled corticosteroids — the ubiquitous puffers — can have side effects, including suppressing the activity of immune cells in the airways. The less the airway is inflamed, the more corticosteroid is absorbed; and the more that's absorbed, the greater the chance of such side effects. This means that people who benefit least from inhalers are at greatest risk of side effects, Bush said.

Even worse, children still die from asthma, in part, because they do not use inhalers they need. Bush and Fleming pin part of the blame on the fact that "the diagnosis of asthma has been trivialized, and inhalers [are] dispensed for no good reason … [becoming] almost a fashion accessory."

Bush and Fleming have a wealth of studies on their side: Gold-standard pulmonary tests keep finding that many people diagnosed with asthma don't have it.

The percentage of children falsely labeled asthmatic can be as high as 90 percent, as a 1996 study of kids with chronic coughs found, or a still-troubling one-third, as a 2008 study of adults reported. Last month, a study from the Netherlands closely examined 650 children diagnosed with asthma and found that 53.5 percent did not have it.

Concern about seeing asthma where it doesn't exist didn't come out of the blue. As far back as 1999, physicians recognized that wheezing — which many parents and even doctors consider the hallmark of asthma — "probably has little in common with asthma and its defining chronic airway inflammation." That's more than an academic point: episodic wheezing, usually caused by a persistent cough from a respiratory infection, doesn't respond to inhaled steroids.

The American Academy of Pediatrics raised the overdiagnosis concern at its annual meeting in 2013.

"Asthma is blown out of all rational proportion," Dr. Michael Seear, an expert in respiratory diseases in children at the University of British Columbia, said in an interview. "There is a small central core of children with real disease but this group is surrounded by a penumbra of imaginary cases," largely because physicians rarely perform rigorous pulmonary tests.

Objective measures of asthma include measuring peak lung flow, airflow obstruction, and airway inflammation, and seeing if asthma medications affect either. But physicians seldom use those tests, Bush said: "They seem to think it's ridiculously easy to diagnose asthma and don't want to bother."

There is strong evidence, from several countries and different age groups, that a large fraction of people who are diagnosed with asthma do not have it.

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