Climate Change Fuels Hay Fever: Pollen Seasons Lengthen and Intensify

Climate change is significantly worsening hay fever symptoms, according to a recent study that highlights the impact of rising temperatures and increased carbon dioxide levels on pollen seasons and allergen exposure. This phenomenon is particularly pronounced among vulnerable populations, making it a pressing public health concern.

A new review published in The Laryngoscope underscores the growing consensus among health professionals that climate change is amplifying the global burden of hay fever, also known as allergic rhinitis (AR). The evidence shows that rising temperatures and elevated carbon dioxide levels are not only extending pollen seasons but also intensifying allergic reactions.

Key findings from the study include:

• Hay fever prevalence is increasing by 2% to 3% annually in industrialized nations.
• The spring pollen season in North America now starts up to 20 days earlier than it did in previous decades.
• A scoping review of scientific literature from 2000 to 2023 focused on the relationship between climate change and hay fever severity.
• Researchers identified 30 studies that met strict criteria related to climatological mechanisms affecting allergy symptoms.

Lead author Alisha Pershad, a third-year medical student at George Washington University, stated, “We were very specific in our inclusion and exclusion criteria. By minimizing variability in our included studies, we were able to improve the strength of our conclusions.”

More than half of the studies reviewed reported longer pollen seasons or increased pollen concentrations directly linked to climate change. A U.S.-based projection suggested that pollen emissions could rise by 16% to 40% by 2100, with pollen seasons extending by an additional 19 days beyond the current increase of 20 days.

In Europe, ragweed pollen, known scientifically as Ambrosia, is also expected to rise due to increasing temperatures. Specific studies have reinforced these connections:

• A 2021 study from Australia highlighted that from 2016 to 2020, daily maximum temperatures, atmospheric CO₂ levels, and the grass pollen index were higher compared to the period between 1994 and 1999.
• A 2017 European model projected that between 2041 and 2060, the number of people allergic to ragweed could grow from 33 million to 77 million, as the plant spreads into new areas.
• A 2025 study in China indicated rising pediatric outpatient visits for AR, corresponding with higher peak pollen levels.

Children are particularly vulnerable to these changes due to greater outdoor exposure, higher respiration rates, and more frequent mouth breathing. The studies also explored underlying mechanisms linking climate change to allergy severity:

• Two studies, one field-based and one lab-based, found that higher humidity and carbon dioxide levels enhance allergenic pollen dispersal.
• Increased rainfall can help reduce pollen levels by cleansing the air.
• Another study revealed that the mold allergen Aspergillus thrives under current CO₂ concentrations compared to pre-industrial levels.

Not all populations are affected equally by these changes. Environmental and socioeconomic disparities mean that Black and Hispanic communities, low-income groups, and older adults are more vulnerable to allergy symptoms. Urban residents, despite having fewer trees and plants, face greater risks due to the urban heat island effect caused by concrete and asphalt. Pershad noted, “Communities historically impacted by environmental inequities such as red-lining tend to live in regions that experience warmer daytime temperatures.”

Mold exposure is another pressing concern, especially in low-income areas, where residents may lack the resources to address water damage promptly, leading to mold growth. “Global warming is exacerbating weather extremes such as hurricanes and flooding, which increases the risk of mold growth, a common environmental allergen,” Pershad added.

Health professionals are increasingly aware of the trend. A 2022 study from Italy found that:

• 56% of pulmonologists reported an earlier and longer pollen season.
• 45% observed an increase in AR patients.
• 61% noticed a rise in pediatric cases.

Nearly all—97%%—expressed a desire to learn more about climate change’s role in hay fever. “Physicians are uniquely positioned to witness the impact of allergic rhinitis on patient outcomes and can adapt their practice as climate change intensifies,” said Pershad. “As trusted voices in the community, they should leverage their frontline experience to advocate for meaningful change in addressing the climate crisis.”

In conclusion, the intersection of climate change and public health is becoming increasingly evident, particularly for individuals suffering from hay fever. As pollen seasons lengthen and allergen exposure increases, it is crucial for health professionals and communities to understand and address these changes to mitigate the impact on vulnerable populations.