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Climate Change, Allergies, and Asthma


Journal of Occupational and Environmental Medicine: December 2011 - Volume 53 - Issue 12 - p 1353–1354
doi: 10.1097/JOM.0b013e318237a00d

Assistant Professor of Medicine and Surgery, Stony Brook University School of Medicine, Stony Brook Allergy & Asthma, Stony Brook, New York

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To the Editor:

Climate change, if present, is associated with atmospheric warming—so-called “global warming”—as well as volatility in weather patterns, leading to more severe winters at a given latitude (since cold air typically further north in latitude is pushed south) and hotter summer months, when the earth is closer to the sun.1 Hot weather generates more pollen from plants.2 Cold weather is associated with asthma emergency department visits in New York City.3 More pollen causes more disease, not only allergically induced, but also nonallergic, since ragweed, for example, produced more reactive oxygen species (ROS), so it may produce inflammation, leading to upper and lower respiratory tract symptoms, even in those persons without allergic asthma, rhinitis, or conjunctivitis.4 Clean Air Act enforcement may reduce sources of anthropogenic heat.5

Does climate change have 2 potentially deleterious effects on human health: (1) prolonged and more severe pollen seasons, leading to (2) worsened asthma and allergies? If true, these downstream consequences may pose significant risks in terms of patient care costs, lost time from work, morbidity, and possible mortality.

  1. For the first question, supporting the possible concept of prolonged and more severe pollen seasons from hot weather, the duration of ragweed pollen season has been increasing as a function of latitude in North America—associated with delay in first frost by 27 days and lengthening of the frost-free period at latitudes above 44°N since 1995.2 In Turkey, daily mean temperature and levels of sunshine are associated with more severe pollen counts.6
  2. Our research group determined that for the latter question—cold weather and asthma—atmospheric temperature indeed impacts New York City asthma emergency department visits. Temperature data were recorded in Central Park from 2000 to 2007. Particulate matter (PM2.5) air pollution data, the concentration of 2.5 micron-sized particles per cubic meter of air were collected from the Bronx, Queens, and Manhattan from 2006 to 2009. Pollen counts were measured in Brooklyn in 2008. We obtained New York City asthma emergency department visit data from NYC. GOV from 2000 to 2007. Relations among these data were determined on the basis of correlation coefficients. There was a reverse relationship between asthma indicators and temperature, that is, extremely low temperature was associated with higher asthma discharge rates in the Bronx.3
  3. Does more pollen cause more disease? Ragweed, known as Artemisia species, pollen represents a major cause of allergy in Central Europe. Variations in the pollen season, the influence of climate variables and the prevalence of pollinosis to it, were analyzed in Poznan, in western Poland between 1995 and 2004. The Artemisia species pollen season grew longer because of a clear advance in the starting day and only a slightly earlier end point; the peak day also came slightly earlier. Temperature was directly correlated with daily Artemisia species pollen levels; relative humidity was inversely correlated. Twelve percent of patients had a positive skin-prick test reaction to Artemisia species. Their symptoms were rhinitis and conjunctivitis (15%), atopic dermatitis (15%), chronic urticaria (14.3%), bronchial asthma (2.4%), and facial and disseminated dermatitis (1.3%). Elevated specific IgE concentrations were detected in the sera of 10.1% of patients. Pollen season intensity was also found to be highly influenced by rainfall in the previous weeks. Trends toward earlier season starts and longer duration, possibly caused by climate change, may have had an impact on this allergic Polish population.4

Another study relates geo-climate effects on asthma and allergic diseases in adults in Turkey (PARFAIT study). Evaluation of 25,843 questionnaires from parents of 25,843 primary schoolchildren in 14 cities indicated that mean annual temperature was significantly associated with the prevalence of asthma and wheezing in both genders. Eczema and temperature were associated in female subjects. Asthma in women was associated with mean annual humidity in the air. Annual number of days with snow was associated with wheezing.7

4. Is there an additional effect of nonallergenic air pollution acting in concert with aeroallergens?

Ragweed has physicochemical properties to release ROS to cause disease, so that a 2 hit hypothesis may come into play. For those not sensitized, ROS may play a role; for those with allergies, ROS plus IgE-mediated disease would enhance the inflammation.8

Changes in production, dispersion, and allergen content of pollen and spores, both region- and species-specific may have been influenced by urban air pollutants interacting directly with pollen.9

While the incidence of allergy and asthma appears to be increasing worldwide, residents of urban areas more frequently experience these conditions than rural dwellers. Outdoor air pollution concentrations result from intense energy consumption and exhaust emissions from automobiles. Urban air pollution is a serious public health hazard. Laboratory studies have confirmed epidemiologic evidence that air pollution adversely affects lung function in patients with asthma. Damage to airway mucous membranes and impaired mucociliary clearance caused by air pollution may facilitate access of inhaled allergens to the immune cells in the airway, thus promoting sensitization of the airway. Consequently, a more severe allergic antibody (immunoglobulin IgE-mediated) response to aeroallergens and airway inflammation could account for increasing prevalence of allergic respiratory diseases in polluted urban areas. The most abundant components of urban air pollution entail high levels of vehicle traffic with airborne particulate matter called PM10 and PM2.5, nitrogen dioxide, and ozone.5 Diesel exhaust is particularly troublesome, since it increases the production of allergic IgE antibodies.10

If the earth's temperature is increasing—from fossil fuel combustion, greenhouse gas emissions from energy supply, transport, industry, and agriculture—then climate change altering the concentration and distribution of air pollutants, and interfering with the seasonal presence of allergenic pollens in the atmosphere, will significantly prolong these periods.11

5. The Clean Air Act gives Americans the opportunity to attenuate anthropogenic climate change like industrial air pollution, thereby alleviating a man-made scourge of heat-induced increased aeroallergen concentrations. I testified before Congress about the need to fund the EPA and the Clean Air Act, and in this letter, I reaffirm my position.5

Anthony M. Szema, MD, FCCP,


Assistant Professor of

Medicine and Surgery

Stony Brook University

School of Medicine

Stony Brook Allergy & Asthma

Stony Brook, New York

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2. Ziska L, et al. Recent warming by latitude associated with increased length of ragweed pollen season in Central North America. Proc Natl Acad Sci USA. 2011;108(10):4248–4251.
3. Chen Y, Forsyth E, Pan K, Szema A, Szema K, Chenrachasit P. Atmospheric temperature and pollen counts impact New York City asthma ER visits. J Allergy Clin Immunol. 2010;125(2,suppl 1):Ab208.
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5. Statement by American Thoracic Society by Anthony Szema before U.S. House of Representatives Committee on Appropriations, Subcommittee on Interior, Environment, and Related Agencies. Fiscal Year 2012, U.S. Environmental Protection Agency, April 5, 2011. Available at: Accessed October 6, 2011.
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10. Diaz-Sanchez D, Dotson AR, Takenaka H, Saxon A. Diesel exhaust particles induce local IgE production in vivo and alter the pattern of IgE messenger RNA isoforms. J Clin Invest. 1994;94(4):1417–1425.
11. D'Amato G, Cecchi L, D'Amato M, Liccardi G. Urban air pollution and climate change as environmental risk factors of respiratory allergy: an update. J Investig Allergol Clin Immunol. 2010;20(2):95–102; quiz following 102.
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