Hay fever, or seasonal allergic rhinitis, affects 17.6 million adults in the United States and results in $11.2 billion in related medical expenses. A new study by University of Maryland School of Public Health researchers shows that exposure to more frequent “extreme heat events” increases the prevalence of hay fever among U.S. adults.
“It is well established that extreme heat events are on the rise, and this trend is projected to continue in response to changing climate,” explained Dr. Amir Sapkota, associate professor in the UMD SPH’s Maryland Institute for Applied Environmental Health and senior author of the study published in the Journal of Allergy and Clinical Immunology in Practice. “Our study is the first to provide evidence of how such increases in extreme heat events contribute to allergic diseases such as hay fever at a national level.”
The study, “Exposure to extreme heat events is associated with increased hay fever prevalence among nationally representative sample of US adults: 1997-2013,” linked National Health Interview Survey Data (1997-2013) with extreme heat event data. The research team identified extreme heat events during 1997-2013 at the county level by comparing the daily maximum temperature (Tmax) to the county and calendar month specific thresholds (95th percentile of Tmax values) that were calculated based on 30 years of baseline data (1960-1989).
The research team used statistical analysis to investigate the association between increased frequency of extreme heat events and hay fever prevalence, taking into account other factors such as age, race/ethnicity, sex, educational level, poverty status, and urban/rural residence. They found that adults in the highest quartile of exposure to extreme heat events had a seven percent increased odds of hay fever compared to those in the lowest quartile of exposure.
“While the exact mechanisms by which long-term exposures to extreme heat events increase the risk of hay fever remain unclear, one potential explanation is changes in plant phenology,” said Dr. Crystal R. Upperman, lead author of the study. “Higher frequency of extreme heat events, particularly in the winter and spring may lead to a longer pollen season as warmer temperatures contribute to earlier onset of greening and flowering of plants — including trees– which are major sources of pollen.”
Researchers found the timing of extreme heat events also made a difference in hay fever rates. The association between exposure to extreme heat events and hay fever was more pronounced for extreme heat events that occurred during the spring season, with evidence of a clear exposure-response relationship. This was not the case for extreme heat events that occurred during the fall season.
While Dr. Sapkota and Dr. Upperman do acknowledge the seven percent increase in prevalence of hay fever as modest, they argue it could have significant implications for millions of people in the United States who suffer from allergy, including decreased quality of life and additional medical expenses.