NEW BRUNSWICK, NJ – Ragweed season began in earnest in the northern United States, with readings reported in Maine since August 3. The progression of ragweed pollen release is expected to proceed south and is expected to reach the New York/New Jersey metropolitan area within two weeks, according to Leonard Bielory, M.D., a specialist in allergy and immunology with the Department of Environmental Sciences at the School of Environmental and Biological Sciences and certified by the American Academy of Allergy, Asthma and Immunology National Allergy Bureau as “a pollen counting station.”

“Over 11 percent of sufferers list ragweed as the sole culprit of their late summer-early fall allergies, but over 60 percent of those with allergies are allergic to ragweed, a trend that has been increasing most in the western United States,” says Bielory. 

This appears to correspond to the potential increase in exposure that Bielory has noted, which reflects increasing ragweed seasons in the west and with recent observations he recently reported at the annual meeting of the American College of Allergy, Asthma and Immunology that skin test reactivity has more than doubled over the past 25 years. In general, three out of four Americans who have allergies are allergic to ragweed pollen, which causes hay fever. Allergies associated with ragweed pollen costs about $21 billion a year in the U.S.

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Bielory is principal investigator on a long-term U.S. Environmental Protection Agency grant to study the potential impact of climate change on the human population, especially allergic airway disease, and what to expect over the course of the next 50 years.

A changing climate means allergy-causing ragweed pollen has a longer season that extends further north than it did just 16 years ago. For the New York and New Jersey metropolitan area, ragweed season has not been as intense with respect to the amount of pollen, but there appears to be increased sensitivity to pollen, Bielory notes.

“Allergies that have been minor in the past are going to increase and become more of a clinical problem that may also impact patients with asthma,” he says.

According to the study published in the Proceedings of the National Academy of Sciences, allergy experts found that ragweed pollen season lasted as much as 27 days longer in 2009 than it did in 1995, with increasing range the further north one got. The result is a more dramatic change in the length of the pollen season, explains Bielory.

At one time this was hypothesized and modeled as a possibility, “but it is a reality; this is affecting patients now,” says Bielory. As global average temperatures have warmed, the first frost has been delayed, especially at higher latitudes, which means a longer season for ragweed. “Because warming is greater at these high latitudes, the length of the season has been more pronounced,” he adds.

According to the report, the ragweed season actually shrank by four days between 1995 and 2009 in Texas, while further north it was noted to be 11 days longer in Nebraska; 16 days longer in Minnesota; and 27 days longer in Saskatchewan, Canada.

In New Jersey, the season appears to have grown longer over the past 20 years, but not as prolonged as the differences noted in Canada. The shift is likely to have an impact on the diagnosis of allergies coinciding with the flu season.

“Primary care physicians may under-diagnose and under-treat allergies since they’d be unfamiliar with the change in the allergy season and may require the assistance of an allergist to confirm the diagnosis and prescribe the most effective treatment for their patients,” says Bielory.

Ragweed is not the only pollen season affected by changing climate. The wide-ranging EPA study will also be evaluating the impact on tree and grass pollen seasons in the early and late spring.

Bielory continues to study the impact of pollen on health along with the Centers of Disease Control and Prevention in the development of a National Pollen Surveillance Network.