Climate Change Effects on Allergy

April 5, 2021
Climate Change Effects on Allergy


I am an allergist in a small community and I have been invited to be part of a panel on a TV current events program to discuss the effects of climate change on allergy in the community. I am aware of some data on the earlier start and prolonged nature of seasonal pollens. Is there good evidence of other changes we can expect?

Climate change is still an ongoing global problem that affects different aspects of human life, including worsening chronic diseases such as allergies or COPD. The comments made above cover almost all the consequences of climate change in allergic patients, especially the one made by Dr. Gennaro D'Amato (his main research field). Therefore, I will include some new data and concepts physicians have about the relationship between climate change and allergies.

It is well known that climate change has many objective indicators such as a change in surface temperature, atmospheric water vapor, severe weather events, the retreat of glaciers, and sea-level rise. Regarding its impact on allergic patients, we can consider the following events that led to increased asthma exacerbations and sensitized people.

First, higher carbon dioxide concentrations (due to air pollution) and warmer temperatures (greenhouse effect) change pollination patterns. For example, there is an increase of Amb a 1 (major allergenic peptide of ragweed) and Bet v 1 (major allergenic peptide of birch). Likewise, an Italian study showed there was a progressive increase in pollen load (25%) over 27 years correlated with increasing temperature (> 30ºC) and increased incidence of pollen sensitivity. Also, pollen seasons have lengthened in North America. A recent study analyzed long-term pollen data from 60 North American states (1990-2018) and found a lengthening of pollen season (+20 days) and an increase in pollen concentrations (+ 21%), all influenced by human activity in climate. The main consequences of this event are severe symptoms and alteration of the seasonality of allergies.

Second, there are more frequent extreme climate events such as thunderstorms, heatwaves, and flooding caused by intensive rain. Thunderstorms can release allergenic particles of respirable size in the atmosphere after their rupture by osmotic shock. During the first 20–30 min, patients with pollen allergies are at risk of inhaling high concentrations of these allergens, which can induce potentially severe asthmatic exacerbations. The most recent event of this phenomenon was in Melbourne, Australia (2016). When more than 9000 patients with asthma exacerbations and thousands of calls to firefighters, police, and general practitioners for asthma symptoms. Heatwaves are more common in urban areas and are explained by the heat island effect (a vast amount of treeless asphalt and large heat-retaining structures that block cooling breezes, increasing surface temperature). They led to fluid loss and rise of pollutants concentrations, causing airway inflammation, bronchoconstriction, and an increase in mortality and morbidity, especially in old patients with COPD. Flooding leading to long-term dampness in residential dwellings promotes fungal growth and, therefore, higher sensitization rates and allergy-independent airway inflammation (glucans, mycotoxins, etc.). For example, after Hurricane Katrina in New Orleans (2005), high indoor and outdoor fungal counts were noted. Increased moisture, higher temperatures, and CO2 levels encourage fungal (mold) growth. The same effect is seen in people living in coastal and wetland areas due to rising sea levels.

Third, air pollution, as one of the main contributing factors of climate change, can also worse pulmonary function, airway inflammation and facilitate IgE sensitization against allergens. Ozone (O3), particulate matter (PM), diesel exhaust particles, NO2, and sulfur dioxide increase the respiratory tract's permeability and facilitate the penetration of allergens into mucous membranes and cause interaction with the cells of the immune system. As a result, air pollution plays an inflammatory role in the airways of predisposed patients. O3 is strongly correlated with summers and hot days (> 32 ºC). It increases the frequency of asthma exacerbations, susceptibility to infection and promotes COPD. Likewise, PM 2.5, PM 10, NO, and NO2 led to the same pulmonary effects as O3. Additionally, air pollutants can adhere to pollen grains and paucimicronic-sized plant particles' surface, changing these agents' morphology and their allergenic potential. These produce airway inflammation by increasing the epithelial permeability and enhance pollinosis by allergens in atopic patients.

Finally, it is also important to highlight that most of the studies carried out are from the northern hemisphere. Although there is limited data about climate change on outdoor and indoor allergens in the southern hemisphere, some characteristics could impact allergies differently, as seen in northern countries. For example, a different increase of maximum surface temperatures influenced by CO2 levels (besides fossil CO2 emissions, CO2 sinks are common, and there is a greater ocean-to-land ratio) may help understand delayed responses to global temperature changes in southern countries, the widespread of northern flora in southern countries such as star weed, and more contribution of grass pollen due to the absence of deciduous trees like birch, ash, poplar or hazel.



  1. Davies JM, Berman D, Beggs PJ, Ramón GD, Peter J, Katelaris CH, et al. Global climate change and pollen aeroallergens: A southern hemisphere perspective. Immunol Allergy Clin North Am. 2021;41(1):1-16.
  2. Anderegg WRL, Abatzoglou JT, Anderegg LDL, Bielory L, Kinney PL, Ziska L. Anthropogenic climate change is worsening North American pollen seasons. Proc Natl Acad Sci U S A. 2021;118(7):e2013284118.
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  4. D'Amato G, Chong-Neto HJ, Monge Ortega OP, Vitale C, Ansotegui I, Rosario N, et al. The effects of climate change on respiratory allergy and asthma induced by pollen and mold allergens. Allergy. 2020;75(9):2219-28.
  5. Cecchi L, D'Amato G, Annesi-Maesano I. Climate change and outdoor aeroallergens related to allergy and asthma: Taking the exposome into account. Allergy. 2020;75(9):2361-63.
  6. Poole JA, Barnes CS, Demain JG, Bernstein JA, Padukudru MA, Sheehan WJ, et al. Impact of weather and climate change with indoor and outdoor air quality in asthma: A Work Group Report of the AAAAI Environmental Exposure and Respiratory Health Committee. J Allergy Clin Immunol. 2019;143(5):1702-10.
  7. Katelaris CH, Beggs PJ. Climate change: allergens and allergic diseases. Intern Med J. 2018;48(2):129-34.
  8. Demain JG. Climate change and the impact on respiratory and allergic disease: 2018. Curr Allergy Asthma Rep. 2018;18(4):22.


Answered by
Crhistian Toribio, MD


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