Climate change is contributing to warming trends that lead to earlier, longer, and worse allergy seasons in cities like Philadelphia, where the allergy season is five weeks longer than it was in the early 1970s.
Your watery eyes, runny nose, and scratchy throat aren’t playing tricks on you: in some parts of the state, allergy season is longer than it used to be.
According to a new report from the climate research group Climate Central, the freeze-free growing season for plants—the time between the last and first freeze, which represents the length of allergy season—has extended by an average of 21 days in 87% (173) of the 198 US cities analyzed from 1970 to 2025.
In Philadelphia, the allergy season has extended by five weeks in that time frame. However in Allentown, the allergy season has shortened by 8 days.
Climate change is contributing to these warming trends that lead to earlier, longer, and worse allergy seasons for millions in the US who suffer from seasonal allergies to pollen, according to Climate Central. More freeze-free days each year give plants more time to grow and release allergy-inducing pollen.
All US climate regions have seen their allergy seasons lengthen—led by the northwest, with an average of 31 more days compared to the early 1970s.
“A longer allergy season is a clear signal of a warming world, driven by carbon pollution,” Climate Central vice president for science, Kristy Dahl, Ph.D, said in a statement. “For millions of Americans, that means earlier, longer, and often more intense allergy seasons that can take a real toll on health and daily life.”
Here’s a look at how allergy season has lengthened in other parts of Pennsylvania:
Central Pa. – +8 days
Erie – +24 days
Harrisburg – +17 days
Pittsburgh – +23 days
State College – +21 days
Wilkes-Barre – +4 days
