Allergy season has gotten longer in D.C.

Allergy season increased in D.C. on average by 20 days between 1970 and 2021, per an analysis from Climate Central, a nonprofit climate news organization.

• That's based on the number of days between the last freeze each spring and the first freeze each fall — essentially, the annual window during which seasonal allergy sufferers are most likely to rely on their antihistamine of choice to get by each day.

The big picture: Allergy season increased on average by 15 days between 1970 and 2021 across about 200 U.S. cities.

Why it matters: The lengthening allergy season is tied to climate change, per Climate Central, with big health ramifications for the roughly one-quarter of Americans who suffer from seasonal allergies — and for respiratory health more broadly.

• "Earlier spring and longer periods of freeze-free days mean that plants have more time to flower and release allergy-inducing pollen," says Climate Central.
• From 1990 to 2018, pollen counts increased by 21% nationwide, with the greatest increases in the Midwest and Texas, according to a 2021 study, Axios' Arielle Dreher reports.

What's next: Ongoing climate change means further deviation from what was once considered the norm.

• "We do expect that areas that haven't previously had substantial pollen seasons will potentially start to experience pollen seasons," William Anderegg, director of the Wilkes Center for Climate Science & Policy at the University of Utah, told Arielle.