Allergic rhinitis, better known as hay fever, is a common allergic condition that affects about 25 million people in the US at a cost of approximately $11.2 billion a year. The main triggers for hay fever include seasonal exposures to allergens such as pollen and mold. In North America, pollen from trees in the spring, grass during the summer months, and weeds during the fall are common culprits that lead to hay fever symptoms. However, the length of the pollen season is largely determine by when these plants flower, and the timing of flowering is sensitive to fluctuations in temperature. This is especially true for plants that flower in the early spring.
But human-induced climate change has created disruptions in weather, and also the seasonal calendar, as to when plants bloom and the spring season begins. Researchers now report that due to these fluctuations and changes, an earlier onset of spring was linked to a increased number seasonal allergies sufferers.
“We found that areas where the onset of spring was earlier than normal had 14 percent higher prevalence of hay fever,” said the paper’s first author, Amir Sapkota, an associate professor in the Maryland Institute for Applied Environmental Health. “Surprisingly, we also found similar risk in areas where the onset of spring was much later than what is typical for that geographic location.”
The study used a large nationally representative sample of community dwelling adults (N = 328,248) to assess the association of climate change and its effect on the timing of spring affected hay fever prevalence from 2002 to 2013.
Dr. Sapoka and his colleagues categorized yearly deviations in start of spring (SOS) for each county in the U.S., and categorized their respective long-term averages as: very early (>3 weeks early), early (1–3 weeks early), average (within 1 week), late (1–3 weeks late) and very late (>3 weeks late).
During the study time period, 8.1 percent or 26,565 of the respondents reported having hay fever. Their results showed that individuals who lived in counties with a very early onset of SOS had a 14 percent higher odds of hay fever compared to those living in counties where the onset of spring was within the normal. In addition, persons who lived in counties with very late onset of SOS had a 18 percent higher odds of having hay fever as compared with those who resided in areas where the SOS was within normal range.
Ethnicity and education level also played a role. Non-Hispanic white adults had a 42 percent higher odds of reporting hay fever during the last year when compared with Hispanic adults, and persons who had a college education were also more likely to report having hay fever in the previous 12 months versus adults with less than a high school education.
The authors note that the reasons for the higher prevalence of hay fever when spring arrives early is probably related an increase in pollen exposure. The earlier that spring arrives means that the trees flower sooner and thus create a longer season for tree pollen. Conversely, in a very late spring onset, a larger number of tree species will simultaneously bloom, causing a very high concentration of pollen for a shorter duration.
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Associations between alteration in plant phenology and hay fever prevalence among US adults: Implication for changing climate.
Last updated on 10/1/19.