Allergy Season Lengthens Across U.S. by 21 Days on Average

Climate data shows plants have more time to grow and release pollen due to longer freeze-free periods.

Published on Mar. 6, 2026

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A new report from Climate Central reveals that allergy season has grown longer across the United States by an average of 21 extra 'freeze-free' days since the 1970s. This extended growing period gives plants more time to produce and release the pollen that triggers seasonal allergies for many people.

Why it matters

Longer allergy seasons can significantly impact public health, leading to more severe and prolonged suffering for those with seasonal allergies. This trend is likely driven by climate change, which is causing temperatures to rise and frost-free periods to last longer in many regions.

The details

The Climate Central analysis looked at data from 242 locations across the U.S. and found that the length of the freeze-free season has increased by an average of 21 days since the 1970s. This extra time allows plants to grow and release more pollen, exacerbating allergy symptoms for millions of Americans.

  • The analysis examined data from the 1970s to the present day.

The players

Climate Central

A non-profit science and news organization that analyzes and reports on climate change and its impacts.

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The takeaway

This research highlights how climate change is extending allergy season across the country, leading to more prolonged suffering for those with seasonal allergies. Addressing the root causes of climate change could help mitigate this growing public health issue in the long run.