According to longitudinal data from the National Health and Nutrition Examination Surveys (NHANES), there have been substantial increases in rates of asthma and allergen sensitivities in the United States in recent decades.1 The prevalence of both conditions roughly doubled during the 20-year period between the second and third surveys (NHANES II and NHANES III).1
Climate change has been cited as a significant factor influencing in these trends. In particular, impact of climate change on pollen season has become a topic of increasing interest. As described in a 2019 report by the American Academy of Allergy, Asthma & Immunology (AAAAI) Environmental Exposure and Respiratory Health Committee, “Changes in patterns of outdoor aeroallergens caused by increasing temperatures and amounts of carbon dioxide in the atmosphere are major factors linked to increased duration of pollen seasons, increased pollen production, and possibly increased allergenicity of pollen.”2
Results of a more recent study support these associations and shed new light on the anthropogenic contribution to these shifting patterns. Investigators used data derived from 60 North American pollen stations from 1990 to 2018, along with earth system model simulations, to estimate the impact of climate change — including the proportion caused by human-driven temperature increases — on the length of pollen season as well as pollen concentrations.3
The results demonstrated temporal increases in annual (20.9%) and spring (21.5%) pollen integrals. The largest increases were noted in Texas and the midwestern region of the United States, and tree pollen was the taxa with the largest increases in both integrals. Additionally, pollen season start dates have advanced by approximately 20 days (P =.01), and length of pollen season has increased by approximately 8 days (P =.0003).
The analyses further revealed that “human forcing of the climate system contributed ∼50% (interquartile range: 19-84%) of the trend in pollen seasons and ∼8% (4-14%) of the trend in pollen concentrations,” the authors reported. These results indicate that “anthropogenic climate change has already exacerbated pollen seasons in the past three decades with attendant deleterious effects on respiratory health.”3
The researchers also note the link between pollen concentrations and medication purchases, emergency hospital visits, and increased susceptibility to viral infections among patients with allergies and asthma. “Thus, while not analyzed directly here, we hypothesize that climate-driven changes in spring and/or annual pollen integrals would have important implications for spatial and temporal patterns of allergy and asthma prevalence and associated medical costs,” they wrote.3
For additional discussion regarding the implications of these findings, we interviewed Kevin P. McGrath, MD, FACAAI, FAAAAI, an allergist-immunologist in private practice in Wethersfield, Connecticut, and National Spokesperson for American College of Allergy, Asthma, and Immunology (ACAAI).
Editor’s Note: This interview has been edited for length and clarity.
Regarding the findings that pollen season length and concentrations appear to have increased in North America as a result of climate change, what are the anticipated effects on asthma and allergy trends, and what are the potential effects on individuals who already suffer from allergies and asthma?
Dr McGrath: As we are seeing longer and more severe pollen seasons and higher pollen counts, we are seeing more patients with increased symptoms of asthma and allergy exacerbations. With asthma we see more wheezing, coughing, shortness of breath, and waking up at night with difficulty getting good sleep. With increased allergic rhinitis symptoms, we see increased fatigue, as fatigue is the most common problem from allergic rhinitis. The inflammation of allergic rhinitis kicks people out of a deep restful sleep, so they never really get restful sleep despite sleeping for 9 or 10 hours. This is the reason why many patients opt for allergy immunotherapy; those who do not often see increased days lost from work or school compared to those on allergy injections.
What are key recommendations for clinicians about how to address these issues in practice?
Dr McGrath: For clinicians treating patients with allergy symptoms, we usually recommend a combination of topical nasal steroid sprays and antihistamines. The most effective nonsedating or low-sedating antihistamines are fexofenadine (Allegra®) 180 mg and levocetirizine (Xyzal®). Cetirizine (Zyrtec®) is not as effective generally as levocetirizine or fexofenadine 180 mg and may cause more drowsiness. Loratadine (Claritin®) is a very weak antihistamine and not often helpful.
Regarding to topical nasal steroid sprays, any of them other than the Flonase that squeezes from the top are effective, namely fluticasone furoate (Flonase Sensimist), triamcinolone acetonide nasal spray (Nasacort AQ), or budesonide (Rhinocort® AQ). The key is proper technique: Patients should spray away from the nasal septum to get the best effect and less irritation when using the nasal steroid sprays properly.
We also recommend exercising early in the morning or late in the day when the pollen counts are at the lowest. We recommend washing hair after being outdoors, as it will attract pollen and then release it into bedding at night when it loses its electrostatic charge. This will often cause increased symptoms upon waking up in the morning.
Using fans in the window or riding with all the windows open in the car will increase exposure to pollen and molds outdoors. Using air conditioning or closing up the rooms and using portable HEPA [high-efficiency particulate air] filters can often be useful. Simply using air conditioning in a car can be quite helpful. At the beginning of the season, it’s helpful to run the air conditioning for about 5 or 10 minutes with the car running and all the doors and windows open to blow out any potential molds or dust that may have accumulated in the central system. If there is a replaceable air filter for intake into the air conditioning system, this should be cleaned or changed as well.
These are short-term solutions. Referral to a board-certified allergist is often useful for evaluation. Do not order blood work for environmental allergens such as pollen, molds, etc, nor foods. An allergy consult will be less costly and far more efficient.
What are other important considerations in treating these patients?
Dr McGrath: Since the natural history of allergies is to get progressively worse over time, year after year and season after season, it’s important for clinicians to know that this year’s allergies will come back next year and will be worse each year after that. It is worth getting an allergy consultation to know what the patient’s various seasons are, as well as potential allergy triggers, both indoors and outdoors.
Although there are many allergy medications available over the counter, proper guidance by a board-certified allergist can often be worth the time and effort to get the best results at the lowest cost in controlling their symptoms. Certainly for many patients, allergy injections are the only thing that reverses the long-term progression of nasal allergies. Allergy injections have also been shown to decrease the rate of patients that go on to develop asthma from uncontrolled nasal allergies for many years.4 I often work closely with many pulmonary physicians in addressing their patients’ allergies, as these will make asthma much more difficult to control.
1. Meng Q, Nagarajan S, Son Y, Koutsoupias P, Bielory L. Asthma, oculonasal symptoms, and skin test sensitivity across National Health and Nutrition Examination Surveys. Ann Allergy Asthma Immunol. 2016;116(2):118-125.e5. doi:10.1016/j.anai.2015.11.006
2. Poole JA, Barnes CS, Demain JG, 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):1702-1710. doi:10.1016/j.jaci.2019.02.018
3. Anderegg WRL, Abatzoglou JT, Anderegg LDL, Bielory L, Kinney PL, Ziska L. Anthropogenic climate change is worsening North American pollen seasons. PNAS. 2021;118(7):e2013284118; doi:10.1073/pnas.2013284118
4. Zhang W, Lin C, Sampath V, Nadeau K. Impact of allergen immunotherapy in allergic asthma. Immunotherapy. 2018;10(7):579-593. doi:10.2217/imt-2017-0138