Is climate change making the allergy season worse?

For millions of people, sneezing, congestion, itchy eyes and fatigue starts to intensify in the spring, when trees begin to pollinate, and extend through mid-to-late fall, when ragweed season reaches its peak.

However, the timeline for seasonal allergic rhinitis, commonly known as hay fever, has expanded in recent years. Experts cite climate change as a contributing factor, saying the warmer temperatures, changes in weather and increased carbon dioxide levels all lead to longer and more severe allergy seasons.

Warmer temperatures extend the growth cycle of plants. The weather causes trees, grasses and weeds to pollinate earlier, and delays the onset of the first frost date—prolonging the duration of the growing season. New research, published in the journal Lancet Planetary Health in March, found that pollen loads and durations have been increasing on three continents over the past two decades as average temperatures have increased.

With the warmer temperatures, and a longer frost-free season, we may be exposed to more allergenic plants, says Michael Phillips, director of allergy programs at Penn Medicine.

“Some plants don’t grow very well in cold climates,” Phillips said. “But now that it’s getting warmer, we are seeing plants in Philadelphia that never used to grow this far north. And since we haven’t been exposed to these plants before, they can be potent allergens.”

The increased exposure may not only exacerbate symptoms for some allergy sufferers, but can cause people who have never had allergies before to experience symptoms, Phillips said. Nearly 20 million adults have been diagnosed with hay fever in the last 12 months, according to the Centers for Disease Control and Prevention, a slight uptick from the 17.6 million who were diagnosed with the condition in 2012.

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