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Is Climate Change Making the Allergy Season Worse?


Each year, millions of Americans brace for the inevitable symptoms: the sneezing, congestion, itchy eyes and fatigue.

For many, the symptoms start 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. In fact, between 1995 and 2011, warmer temperatures in the United States caused the pollen season to increase by 11 to 27 days, according to the Asthma and Allergy Foundation of America. The findings were corroborated by new research, published in the journal Lancet Planetary Health in March, which 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, MD, 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.

Similar to many cities nationwide, Philadelphia is experiencing peak tree pollen season now. Since March 19, the city has had “very high” levels of pollen every week day, according to the Weather Channel, which provides a five-day allergy forecast.

The high levels of pollen may stem, in part, from the increased levels of carbon dioxide in the atmosphere. When exposed to warmer temperatures and higher levels of CO2, plants grow faster and produce more pollen, says Phillips. The pollen is more potent, too. He noted that airborne pollutants also fuel pollen production. For example, a ragweed plant that grows near a source of pollution will produce twice as much pollen as an identical ragweed plant that’s 20 to 30 miles away.    

Strategies to reduce symptoms

While the allergy season is growing longer and more severe, management strategies and avoidance measures can help people reduce their symptoms.

Preventive measures, including allergy medications, are particularly helpful for people with hay fever. Scott Feldman, MD, PhD, an assistant professor of Clinical Medicine, told the Philadelphia Inquirer he advises patients who are allergic to tree pollen to start their allergy medications around Valentine’s Day – before the symptoms start.

Feldman said allergy shots are fairly effective. Nasal sprays and oral antihistamines generally help to lessen the symptoms, too, as long as they are used correctly and regularly. When using nose spray, you want the spray to go into your sinuses and stay in your sinuses. Sniff gently.

“What you don’t want to do is spray your septum, in the middle of your nose, because that’s not where the allergic reaction is happening,” he said. “The other thing is, many people are overachievers and feel the need to snort their medication strongly. That causes a lot of the medication to go down into the back of the throat. If you’re tasting the medication, that means it is ending up in your throat and not in your nose.”

Beyond using medications, it’s important for people to minimize their exposure allergy triggers. For example, Feldman says, pollen counts tend to peak in the morning. Don’t cut the grass early in the morning, or leave a bedroom window open overnight when pollen counts are high.

After spending time outside, you should shower and wash your clothes, Phillips says. Otherwise, the pollen on your skin and clothes can transfer to your pillow, blanket and other items throughout your home. Keep the indoor air clean by using an air conditioner with a high-efficiency filters. Change the filters regularly.

“It’s really important for people to be cognizant of the weather changes, and the impact it has on allergies,” Phillips said. “As the pollen count continues to climb, and allergy seasons grow more severe, we want people to be aware of how they can minimize the impact of allergy triggers.” 

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