Boise and San Diego Top List of Worst Cities for Allergies

Experts say climate change is driving longer, more intense allergy seasons across the U.S.

Apr. 9, 2026 at 1:10am

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An extreme close-up X-ray photograph showing the delicate internal structures of allergy-causing plants, with ghostly glowing lines and organic textures against a dark background, conceptually illustrating the scientific and clinical nature of the allergy crisis.As climate change drives longer and more intense allergy seasons, X-ray imagery reveals the complex inner workings of the plants responsible.San Diego Today

According to the Asthma and Allergy Foundation of America, Boise, Idaho and San Diego, California are now the top two worst cities in the U.S. for allergy sufferers. Experts say warming temperatures, increased rainfall, and a longer growing season are causing pollen counts to rise dramatically, leading to more intense allergy seasons nationwide.

Why it matters

Allergies impact about one in three Americans, and the worsening allergy seasons driven by climate change are making life more miserable for millions of people. This trend raises public health concerns and highlights the need for better allergy management strategies and policies to address the root environmental causes.

The details

The Asthma and Allergy Foundation of America determines the worst allergy cities based on pollen counts, over-the-counter medication usage, and availability of allergy specialists. This year, Boise and San Diego topped the list, a surprise compared to previous years when southeastern cities typically dominated. Experts say the change is due to tree pollen seasons starting earlier and peaking higher in the western U.S. due to warming temperatures and increased rainfall.

  • In 2025, Boise was ranked 95th and San Diego was ranked 97th on the list of worst allergy cities.
  • This year, Boise and San Diego have risen to the top two spots on the list.

The players

Hannah Jaffee

Research director for the Asthma and Allergy Foundation of America.

Pollen.com

A data source used by the Get the Facts Data Team to analyze pollen levels across the country.

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What they’re saying

“Unfortunately, it's kind of this triple threat of pollen seasons getting longer, more intense, and then also affecting people more.”

— Hannah Jaffee, Research director, Asthma and Allergy Foundation of America

“We saw about half of the cities in the top 20 this year were in the western half of the U.S. That is not something we typically see.”

— Hannah Jaffee, Research director, Asthma and Allergy Foundation of America

What’s next

Experts recommend that people monitor pollen counts and take steps to limit exposure, such as wearing hats and sunglasses, removing shoes before going indoors, and showering at night. However, they caution that allergy impacts can vary greatly from year to year due to weather and climate changes.

The takeaway

This case highlights the growing public health concerns around the worsening allergy seasons driven by climate change, and the need for better allergy management strategies and policies to address the root environmental causes.