Allergy season is getting longer and worse

What's happening: Spring allergy season in the U.S. typically starts in late March and lasts through early June. But in recent years, the spring allergy season has expanded on the front and back end in some places: starting early in late February and lasting into late June.

• Fall allergy season, when ragweed pollinates, might now begin in August too, instead of in September.
• Soaring pollen counts are "really changing the landscape of allergies," says Neeta Ogden, a clinician allergist and spokesperson for the Asthma and Allergy Foundation of America.
• From 1990 to 2018, pollen counts increased by 21% nationwide, with the greatest increases in the Midwest and Texas, per a 2021 study.

The big picture: About a quarter of U.S. adults suffer from seasonal allergies, according to data from the Centers for Disease Control and Prevention, but certain parts of the country have historically had worse allergy seasons.

• The Midwest, East Coast and parts of Texas boast many "allergy capital" cities where pollen presence, allergy medication use, and the number of allergy specialists is highest, per a 2023 Allergy and Asthma Foundation report. In 2023, Wichita, Kansas, and Dallas lead the list.
• Seven Florida cities are ranked in the top 20 on the "allergy capital" list. No cities west of Texas were considered "allergy capitals."

Yes, but: That could start to shift with climate change, especially in typically cooler areas where the temperature now dips below freezing fewer days during the winter.

• One analysis that has not yet been peer-reviewed from Climate Central, a climate science research group, found the number of freeze-free days is increasing nationwide. In the western U.S., the freeze-free season has lengthened by 27 days since 1970, the most of any region, the analysis found.
• With fewer freezing days, plants have a longer season to grow and pollinate, lengthening pollen and allergy seasons.
• "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 and Policy at the University of Utah, told Axios. "As seasons get longer, climate change is moving some plants northward."

Zoom out: Human-caused climate change has many impacts on our health, from its effects on drinking water to air quality.

• The combination of extreme heat and air pollution, a potential in the West during wildfire season, increases mortality risk.
• Warmer weather also breeds public health risks from diseases like the West Nile Virus or Lyme disease, carried by mosquitoes and ticks that thrive in warmer conditions.
• The climate-changed fueled health crisis necessitates a change in the health care system, which will be costly, with estimates at more than $800 billion annually.

How it works: Pollen and mold levels both contribute to commonly experienced allergy seasons in the U.S., and increasing heat and carbon dioxide levels create an environment for both to thrive.

• The West Coast received a record-breaking amount of rain and snow this winter, which could lead to a more severe allergy season as people are potentially exposed to more pollen and mold.
• In the same 2021 study that found pollen counts increasing in recent decades, Anderegg and his colleagues found that pollen seasons lasted longer and had more intensity throughout North America revealing that "climate change has already exacerbated pollen seasons in the past three decades with attendant deleterious effects on respiratory health."

The bottom line: "The decisions we make to tackle climate change more aggressively will help us confront pollen seasons," Anderegg said.

Editor's note: This story has been corrected to reflect that goldenrod does not cause seasonal allergies.