Millions who've experienced asthma symptoms in the past carry around inhalers in case breathing problems arise, but a new study shows that a lot of them might not actually need to.

In a new study, one-third of adults who had been diagnosed with asthma in the last five years were found to show none of the signs of the disease, which suggests the asthma was either originally misdiagnosed, or has since cleared up.

The researchers hope the findings can teach doctors more about how to identify and treat asthma, which is well-known for being difficult to diagnose correctly.

It also shows that not all those who have experienced the symptoms of asthma necessarily have to take medication for their entire lives.

But the team, led by respirologist Shawn Aaron from the University of Ottawa in Canada, warns against throwing away your inhaler right off the bat - any changes in your asthma treatment should be made in the consultation of your doctor.

"It's impossible to say how many of these patients were originally misdiagnosed with asthma, and how many have asthma that is no longer active," explains Aaron.

"What we do know is that they were all able to stop taking medication that they didn't need - medication that is expensive and can have side effects."

The researchers examined 613 randomly selected asthma patients in Canada, all of whom were of adult age, and had been given an asthma diagnosis sometime in the past five years.

Of this group, 410 people (67 percent) had their asthma diagnosis confirmed, whereas 203 (33 percent) were no longer showing any signs of the condition.

Only a third of those 203 were taking asthma medication daily, so in some cases, they might have already noticed an improvement in their symptoms. Meanwhile, half of the 410 with confirmed asthma were using medication on a daily basis.

Among the 33 percent who no longer showed any signs of asthma, treatments were reduced during the study, and then stopped altogther if possible, with follow-up tests monitoring the event of a recurrence.

When this asthma-free group was assessed for the study, some were diagnosed with minor conditions like allergies and heartburn, but 27 percent of the patients were found to have nothing wrong with them at all.

Researchers also dug into the medical records for their volunteers, and found that in 49 percent of cases, the official airflow test required by medical guidelines - called a spirometry test - had not been run.

In a spirometry test, patients are asked to breathe out, and they are measured for the amount of air exhaled in 1 second, and the total volume of air you can exhale in one forced breath, then repeat the process after a puff on an asthma inhaler.

If there's an improvement the second time around, it's a sign that there's an airflow obstruction that can be helped by medication.

Skipping the spirometry test seems to have played a part in the cases of misdiagnosis, as patients who weren't given the test had a higher likelihood of having their asthma ruled out later on.

Only 43.8 percent of people whose diagnosis was ruled out had undergone spirometry at diagnosis, compared to 55.8 percent of people whose diagnosis was confirmed at reassessment.

There are limitations to the study to bear in mind: it only involved Canadian asthma patients, and that can't necessarily be taken as representative of how prevalent the disease is in other countries.

That said, the sample size is large enough to be significant, and the researchers have advice for both those with asthma, and those diagnosing it.

"Doctors should always order spirometry and appropriate lung function tests in anyone they suspect to have asthma," Aaron told Michelle Kuepper at ResearchGate.

"Doctors should also try to follow asthma treatment guidelines and reassess and taper asthma medications in patients who have been controlled for three months."

And if you have been diagnosed with asthma in the past, the team advises going to the doctor and reassessing if your symptoms - such as shortness of breath - have been improving, especially if you didn't get a spirometry test the first time around.

But remember that asthma can be deadly, so you should never adjust your medication without consulting your doctor.

"We need to educate physicians and the public to get the diagnosis right in the first place," says Aaron.

The research has been published in the Journal of the American Medical Association.