Self-reported asthma rates are believed to be at a nine-year low.

About 7.4 percent of the U.S. population reported that they had asthma in 2013, compared with 8.5 percent in 2009, a U.S. Centers for Disease Control and Prevention (CDC) survey found, Reuters reported.

This statistic would indicate a drop of three million children and adults suffering from asthma. Last year 3.8 percent of the U.S. population believed they had suffered an asthma attack, which is a lower number than has been seen in about a decade and a half.

Asthma most commonly causes symptoms such as "wheezing, breathlessness and coughing," Reuters reported.

Black children showed the most prevalent decline in instances of asthma and its symptoms; the asthma rate fell from 16.4 percent in 2012 to 13.1 percent last year.

The researchers are unsure if this means asthma is actually on the decline

"We've all been kind of scratching our heads" CDC statistician Jeannine Schiller told Reuters. "We have no reason not to believe it, but I think it is important to just be cautious about it."

The finding could be a "Statistical blip," Healthday reported. Schiller wants to wait until this year's data comes in before making a final determination about the issue.  

The CDC National Health Interview Survey encompassed 47,000 participants across the United States.

Asthma is one of the most common long-term diseases In children, but many adults struggle with it as well.

Medical researchers are still not sure of exactly what causes the condition, but it is believed to be exacerbated by environmental factors such as "tobacco smoke, cockroaches and mold," Reuters reported.

The CDC recommends finding an asthma treatment that is right for each individual patient.

"The important thing to remember is that you can control your asthma. With your doctor's or other medical professional's help, make your own asthma action plan (management plan) so that you know what to do based on your own symptoms. Decide who should have a copy of your plan and where he or she should keep it," the CDC stated on their website.