Are Allergy Seasons Getting Worse Every Year?

It seems that every year, the news keep stating that this allergy season will be worse than ever before. Is this typical media hyperbole, or is it actually true?

Unfortunately, allergy seasons ARE actually getting worse every year due to a variety of factors, but the root reason is because the pollen count IS truly getting higher every year. With higher pollen counts, allergies become more severe. Not only that, but the pollen itself has become more allergenic over time as well.

Why has the pollen count been increasing every year and how are they becoming more allergenic?

#1: Climate Change

First and foremost is climate change. As temperatures overall get warmer, the warm weather lasts longer which results in a longer growing season for plants. From 1990 to 2018, the pollen season in North America has been estimated to have started 20 days earlier and are 10 days longer now than before [link]. With longer growing seasons, the seasons themselves start to overlap causing a phenomenon known as "season creep." Tree pollen which occurs mainly in the spring begins to overlap with the grass pollen which mainly occurs in the summer. The grass pollen itself can then overlap with the ragweed pollen which mainly occurs during the fall. With overlap, you have more than one pollen types present which can make allergy sufferers feel even worse.

Higher temperatures in and of itself can also lead to earlier and greater pollen production by plants not solely attributable to increased plant biomass, though that can also concurrently occur.

#2: Milder Winters

Related to climate change, a mild winter can trigger pollen release earlier than normal. Researchers have shown that pollen release is delayed with negative soil temperatures as well as snow coverage. Furthermore, any pollen already released can be destroyed by frost and snow resulting in a noticeable decrease in pollen counts. As such, a mild winter can result in a larger than normal increase in pollen.

#3: Increasing CO2 Levels

We know that sunlight combined with carbon dioxide fuels plant growth. With more plant growth, we get more pollen production. Furthermore, carbon dioxide in the atmosphere has increased more than 25% over the past 50 years mainly due to carbon emissions caused by humans. Researchers have also estimated that there is now 21% more pollen compared to 1990. By 2050, airborne ragweed concentrations could be about four times higher than they are right now. This tsunami of pollen into our future does not bode well for allergy sufferers.

#4: Air Pollution

Increased air pollution is also to blame for worsening allergies. You might think that living in a big city without many trees is better for allergies, but that’s simply not true. Common pollutants like ozone and sulfur dioxide, which are produced by vehicles and industrial plants, can irritate the airways and make it easier for pollen to penetrate the mucosal linings of the nose and lungs.

Interestingly, air pollution can also increase the amount of allergenic proteins expressed by the pollen itself. So now, not only is there more pollen, but the pollen itself is becoming a more potent allergen.

#5: Decreasing Bee Populations

A typical-size honey bee colony (approximately 20,000 bees) collects about 57 kg of pollen per year. A colony's annual requirement for pollen has been estimated to range from 15 to 55 kg as pollen is a bee's main source of protein and key for young bee development.

However, there has been a serious collapse of bee populations which can adversely contribute to not only increasing pollen counts, but also create pressures on the type of vegetation that ultimately thrives.

Things you can do to minimize allergy symptoms in the meantime include environmental controls, allergy medications, and allergy shots.

Much thanks to Jamie Allen, PhD Candidate in Environmental Social Sciences, Ohio State University, in her assistance in writing this blog article.

References:

Anthropogenic climate change is worsening North American pollen seasons. PNAS February 16, 2021 118 (7) e2013284118; https://doi.org/10.1073/pnas.2013284118

Warming due to carbon dioxide jumped by half in 25 years. NOAA. 5/18/16

Effects of climate change and seed dispersal on airborne ragweed pollen loads in Europe. Nature Climate Change, 2015; DOI: 10.1038/nclimate2652

Effects of environmental factors on pollen production in anemophilous woody species. Trees 25:253–264

Parietaria judaica flowering phenology, pollen production, viability and atmospheric circulation, and expansive ability in the urban environment: impacts of environmental factors. Int J Biometeorol 55:35–50

Common ragweed (Ambrosia artemisiifolia L.): allergenicity and molecular characterization of pollen after plant exposure to elevated NO2. Plant Cell Environ 39:147–164