Is Global Warming Extending Allergy Season?

Environmental factors may be producing more allergens and making them stronger

More and extra-powerful pollen isn’t the only climate-change link to allergies. Mark Jacobson, a professor of civil and environmental engineering at Stanford University, recently published study findings in Environmental Science & Technology that describe a “carbon dioxide dome” from traffic and industrial pollution that forms around cities, raising not only temperatures, but levels of ozone and particulate matter—a mix of chemicals, acids, metals, soil and dust that finds its way deep into the lungs of people who breathe it in. Consequently, allergies and their relative, asthma, are a particular problem for residents of urban areas, especially kids, who inhale both particulates and the pollen that attaches to them.

“Heat means more ground-level ozone has formed, which primes the lungs for an allergic response,” Epstein said. “The diesel becomes a great delivery system for these allergens, and they are allergenic themselves as well.”

It’s unclear whether allergies have truly become more common over the last few decades. While the most recent data from the National Center for Health Statistics (NCHS) shows that prevalence actually fell between 1997 and 2008, from about 9 percent to 7 percent of U.S. adults, it’s difficult to compare those figures to the 1970s because the information was collected differently then, an NCHS spokeswoman says. In Europe, where environmental triggers are similar, scientists have found an increase in seasonal allergies in several cities. Genetics, of course, also play a role in whether you’re likely to develop an allergy; if both your parents have allergies, you have a 70 percent chance in developing them, too, says Michael Blaiss, M.D., clinical professor of pediatrics and medicine at the University of Tennessee Health Science Center in Memphis.

But environmental conditions help determine whether that hereditary predisposition turns into a true problem. Frequent exposure to any allergen, such as ragweed, pollen, dust or mold, can overwhelm people who may not have previously reacted to it, Epstein said.

“It stands to reason that if there’s more pollen out there, it has more allergic potential, and people who are allergic are going to have worse disease,” Shea says.

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