It is well known that pollen is the cause of allergic disease, including respiratory allergies, and is responsible for causing symptoms in 10-30% of the population. That’s why it’s important to understand pollen, why it is important for allergies, how it is counted and how climate change is impacting pollen counts.
Medical historians credit John Bostock as the first person to describe hay fever. He reported his own case and published his report in 1829 describing 28 patients with symptoms of ‘catarrhus aestivus.’ In the mid-1800s, Charles Blakely, also a hay fever sufferer, did experiments using a microscope and was able to show that the dust particles causing symptoms contained pollen. He also applied the pollen to his nostrils and conjunctiva, replicating symptoms. He was the first to describe a positive allergy skin test applying pollen to abraded skin in 1869.
In 1930, August Thommen outlined five postulates characterizing clinically important pollen types. He proposed that the pollen should cause hay fever symptoms, it should be wind-blown and be able to ‘travel considerable distances,’ there must be a sufficient quantity, and the plants producing the pollen should be widely distributed.1 We still recognize these postulates as being relevant today, and allergists continue to monitor pollen counts to help determine what is triggering symptoms in our patients.
How is Pollen Monitored?
It is important for allergists to know what triggers their patients’ allergy symptoms, therefore it is critical to understand the floristic zones and what plants may be allergenic. In metro Atlanta we are in the Piedmont Forest, so the medically relevant pollens include hardwood trees in the spring, grasses in late spring and summer and weeds, especially ragweed, in the fall.
Our pollen station uses glass rods in a Roto-Rod device, which collects pollen over the prior 24 hours. Then the rods are examined under a microscope to count the different types of pollen. (See Figure 1.)
Interestingly, in 2009 our pollen station found an unusual increase in tree pollen in the fall. After careful investigation, we confirmed that Chinese Elm tree pollen is relevant in the fall here in Atlanta.2 This type of tree is considered an ornamental and has been increasingly used by landscapers in recent years, explaining the changing aeroallergen impact. This finding underscores the importance of understanding potential allergen triggers for allergic symptoms.
Can Pollen Load be Changed?
In December 1956, the New York City Department of Health conducted a borough-wide program of ragweed eradication to reduce atmospheric pollen concentrations. The goal was to ultimately lower allergy symptoms in the area’s residents.
Ninety-seven percent of the ragweed acreage in the Bronx was treated chemically for a total cost of $92,000 (approximately $800,000 in today’s dollars). When pollen counts were analyzed, it was determined that despite these efforts, atmospheric pollen concentrations in the Bronx were at the same levels as prior to the ‘treatment’ and no different than nearby boroughs of Brooklyn and Queens, where there were only “token” programs of ragweed eradication. Clearly, one can’t fool mother nature!
Climate Change and Pollen Counts
There have been several reports confirming that changes in temperature, carbon dioxide levels, rainfall and humidity have profound impacts on the duration of pollen seasons and consequently, the overall pollen load. Reports from Europe suggest that over the last 10-45 years, there has been a 4–6-day advance in plant blooming.3 Italian scientists documented an 18+ day prolongation of tree pollen season over a 27-year period.4 A comprehensive study in the United States examining pollen counts over 16 years found a 3 day earlier start of pollen season with average peak counts increasing over 40% during that time.5
Other factors such as pollen allergenicity and plant microbiome are also impacted by climate changes. Pollen allergenicity/potency is enhanced by elevations in air pollutants and carbon dioxide, which also impacts plant biomass.6
Earlier this year, data from climate and pollen researchers showed that anthropogenic climate change is worsening North American pollen seasons over a 28-year period. Applying data from 60 pollen-counting stations, including ours at Atlanta Allergy & Asthma, the study utilized modeling simulations and found that there was lengthening of pollen seasons by 20 days and increases in pollen concentrations by 21%, which was strongly linked with climate warming.7
Allergy patients have IgE immunologic sensitivity to a variety of allergens, including inhalant pollens that cause their symptoms. Understanding the regional floristic zones and the patient’s exposure is critical in determining potential treatment, including disease-modifying allergen immunotherapy.
At Atlanta Allergy & Asthma, we publish pollen counts daily on our website at atlantaallergy.com to help all patients and providers recognize what may be impacting their allergy symptoms. Recent data demonstrates the impact of warming climate trends contributing to earlier pollen seasons with increased pollen counts. This is disturbing and suggests the need to be vigilant in recognizing these climate changes and how they impact our patients.
1. Thommen AA. The etiology of hay fever: studies in hay fever. NY State J Med 1930;30:437-442.
2. Shams M, Fineman S. High Chinese elm pollen counts in the Fall in Atlanta, Georgia, 2009-2015. Ann Allergy Asthma Immunol 2016;117:553-554.
3. Emberlin J, Detandt M, Gehrig, et al. Response in the start of Betula (birch) pollen seasons to recent changes in spring temperatures across Europe. Int J Biiometeorol. 2002;46:159-170.
4. Ariano R, Canonica GW, Passalacqua G. Possible role of climate changes in variatins in pollen seasons and allergic sensitizations during 27 years. Ann Allergy Asthma Immunol. 2021;104:215-222.
5. Zhang Y, Bielory L, Mi Z, et al. Allergenic pollen season variations in the past two decades under changing climate in the United States. Glob Chang Biol 2015;21:1581-1589.
6. Ziska LH, Gebhard DE, Frenz DA, et al. Cities as harbingers of climate change: common ragweed, urbanization, and public health. J Allergy Clin Immunol 2003;111:290-295.
7. Anderegg WRL, Abatzoglou JT, Anderegg LDL, et al. Anthropogenic climate change is worsening North American pollen seasons. PNAS 2021;118: e2013284118.