Sept. 22 (HealthDay News) -- Although many parents already know that changes in the weather can cause their children's asthma symptoms to flare up, a new study backs up their intuition.

If the humidity levels in the air rose by more than 10 percent or if the temperature increased by more than 10 degrees Fahrenheit in a single day, more children ended up in the emergency department of a Detroit hospital reporting asthma symptoms, the new research found.

"Parents need to be mindful of days when there are dramatic changes in temperature or humidity. A child's asthma may flare more on those days," said study senior author Dr. Alan Baptist, director of the University of Michigan asthma program, in Ann Arbor.

The findings were published in the September issue of the Annals of Allergy, Asthma & Immunology.

As many as 9 million children in the United States have asthma, according to the background information in the study. There are numerous known triggers that can exacerbate the inflammatory airway disease, including viral infections, air pollution, exposure to tobacco smoke and airborne allergens, such as pollen, the study authors noted.

Baptist said that another asthma trigger reported by many parents is weather changes. While some past studies have looked at this phenomenon, Baptist and his colleagues pointed out that none of the previous studies controlled for air pollution and airborne allergens.

For the current study, the researchers reviewed data from two years of emergency department admissions for asthma at Children's Hospital of Michigan in Detroit. During the study time period -- Jan. 1, 2004 through Dec. 31, 2005 -- more than 25,000 youngsters between the ages of 1 and 18 were admitted for an asthma exacerbation, according to the study. That works out to about 35 children a day, according to Baptist.

The researchers then reviewed weather data for that time period, along with data on airborne allergens and air pollution. And, their statistical model was designed to control for these factors, Baptist added.

"A 10 percent increase in humidity two days before the admission day was associated with one additional visit to the emergency department," said Baptist. "For temperature, an interday change of 10 degrees one day before the admission resulted in two additional visits."

Although previous studies have found an association between barometric pressure and asthma symptoms, the current study found no link.

Asked why weather changes might affect asthma symptoms, Baptist said, "Asthma, at its core, is inflammation of the airways, and maybe these changes could be triggering more inflammation. But, it's really unknown why temperature and humidity changes exacerbate asthma, and it should be looked at further."

"This study brings up good discussion points, but I don't think this is going to be strong enough evidence to change practice," said Dr. Shean Aujla, a pediatric pulmonologist at Children's Hospital of Pittsburgh.

Aujla said that cold air is a known trigger for asthma, and confirmed that many parents say a change in weather triggers their children's asthma symptoms.

Until more research is done, she recommended focusing on each child's individual symptoms. "If your child is going outside to play and having persistent symptoms, they should use their albuterol inhaler whether or not it's humid," said Aujla.

And, she added, very few children need to stay inside because of their asthma and weather changes. "Unless a child has very severe asthma, I wouldn't say stay indoors," she said.

SOURCES: Alan Baptist, M.D., M.P.H., assistant professor, and director, asthma program, University of Michigan, Ann Arbor, Mich.; Shean Aujla, M.D., pediatric pulmonologist, Children's Hospital of Pittsburgh; September 2009 Annals of Allergy, Asthma & Immunology