Your Allergy Season Is Getting Longer—Here's Why Climate Change Is to Blame

Climate change is making allergy seasons significantly longer and more intense across the United States. Since 1970, the freeze-free growing season has lengthened in 87% of analyzed cities, giving plants more time to produce the pollen that triggers seasonal allergies in about one in four adults and one in five children.

How Much Longer Are Allergy Seasons Getting?

The numbers are striking: 172 out of 198 U.S. cities analyzed saw their freeze-free seasons extend by an average of 20 days since 1970. In 70 cities, the time between the annual last and first freeze grew by at least three weeks. Some cities experienced dramatic changes, with Reno, Nevada seeing 96 more freeze-free days, while Las Cruces, New Mexico gained 66 additional days.

Regional differences show the Northwest and Southwest leading the charge, with average increases of 24 and 20 days respectively. Cities across the South, Southeast, Ohio Valley, and Northeast now experience the longest freeze-free seasons, averaging between 180 and 231 days per year.

Why Is This Happening?

The culprit is carbon pollution from burning coal, oil, and methane gas, which traps heat in the atmosphere and contributes to spring warming trends. A 2021 study found that human-caused warming was the primary driver of North American pollen seasons lengthening by 20 days on average from 1990 to 2018.

But it's not just about longer seasons—climate change is making allergies worse in multiple ways:

• Extended Growing Periods: Warmer temperatures mean plants start producing pollen earlier in spring and continue later into fall
• Increased Pollen Production: Higher levels of carbon dioxide in the air can boost pollen production, particularly in grasses and ragweed
• Future Projections: With continued high rates of carbon dioxide pollution, the U.S. could face up to a 200% increase in pollen production by the end of this century

What Does This Mean for Your Health?

The health implications are serious, especially for children. Around 19% of children in the U.S. suffer from seasonal allergies, experiencing symptoms like sneezing, coughing, itchy or watery eyes, and runny noses. Pollen also triggers asthma, which affects 6.5% of children, with allergic asthma being the most common type.

These burdens aren't equally shared. Black and Puerto Rican children are between two and three times more likely to have asthma than white children, putting them at higher risk for allergic asthma complications.

Meanwhile, the science behind these reactions involves complex interactions between inflammatory cells and chemical mediators. Histamine, produced primarily by mast cells, plays a central role in allergic responses by regulating immune cell functions and directing their migration to target sites where they cause chronic inflammation.

Parents and caregivers can take protective steps by responding to symptoms rather than expecting traditional seasonal patterns, checking local air quality reports before outdoor activities, using high-efficiency particulate air filters indoors, and supporting efforts to reduce carbon pollution from fossil fuels.