Respiratory allergic diseases, such as seasonal rhinitis and asthma, have almost doubled in the last 20 years in industrialized countries. Raphaëlle Aubert discusses why allergies are getting worse in an article on the Le Monde website.
How climate change is making our allergies worse
Between April and May, the birch pollen season is in full swing. Eyes water, throats sting, noses run: doctors call these immune reactions “allergic rhinitis.” In France, nearly one adult in three is said to suffer from a pollen allergy, according to the French National Agency for Food, Environmental and Occupational Health Safety (ANSES).
Is this a higher rate than before? As early as 2008, an epidemiological study confirmed that pollen rhinitis had tripled in France in 25 years. A few years later, ANSES wrote in a 2014 report that “the prevalence of respiratory allergic pathologies such as seasonal rhinitis and asthma has almost doubled over the last 20 years in industrialized countries.”
Climate change is one of the possible explanations for the explosion in allergies. In spring, so-called “anemophilous” plants release large quantities of pollen in order to reproduce, relying only on the wind to transport them to female catkins, the flowers of these trees.
For allergy sufferers, the risks extend over almost the whole year, varying according to the climate of each region. “The most problematic pollens in France are those of cupressaceae [cypress family] in the southeast, grasses throughout the country, betulaceae [birch family] in the northeast, and mugwort in the Rhone valley,” wrote ANSES.
The overall rise in temperatures is influencing the length of pollen seasons. While scientists point out that the effects of climate disruption “are impossible to reduce to a single pattern” for all plant species, they agree that trees like hazelnut, alder, cypress, and to a lesser extent birch and ash that bloom fairly early in the year, have tended to start their pollen season earlier and earlier.
This year, the surveyors of the National Network of Aerobiological Surveillance (RNSA) have “detected grains of hazel pollen as early as the end of December, while normally they were observed more in February,” Samuel Monnier, the organization’s head of communication explained to Le Monde. However, with winters becoming increasingly mild, in the long run, the opposite could occur: if plants don’t meet their cold weather needs quickly enough, their revival in spring could be delayed.
More pollens and allergens
Even more glaringly, the increased presence of carbon dioxide (CO₂) in the atmosphere is boosting pollen production. The greenhouse gas is necessary for photosynthesis. As early as the 2000s, a team of researchers measured ragweed pollen production based on the plant’s exposure to different levels of CO₂. According to their results, current CO₂ concentrations have increased pollen production by 131% compared to the pre-industrial period. If the rate in the atmosphere reaches the levels projected for the 21st century, production would increase by as much as 320%.
Pollen grains are not only become more numerous, but also more allergenic. “It has been observed that the amount of allergens in birch and ragweed pollen grains has increased with temperature,” wrote ANSES.
The increased presence of chemical pollutants in the atmosphere, especially in cities, also aggravates the situation, by deforming or damaging the wall of some pollen grains. These “pollen grain fragments and cytoplasmic granules are small enough to penetrate the respiratory system much deeper than the pollen grains,” said the same report. Air pollution also acts as an irritant on the respiratory tract, weakening it and exacerbating symptoms.
New plant geography
Finally, the changing climate allows some species to migrate to new regions previously spared from high amounts of pollen. Scientists are particularly concerned about ragweed, a highly invasive species introduced to Europe in the late 19th century.
According to Dr. Iain Lake’s team at the University of East Anglia which modeled the spread of the species in the future, “the largest proportional increases are going to occur in countries where sensitization [to ragweed pollens] is uncommon,” such as France and Germany. In 2020, ANSES estimated that between 1.15 and 3.5 million people are likely to be allergic to ragweed pollen in mainland France.
Difficult to contain, these phenomena raise public health and cost issues. Allergist Jean-Marie Nguyen, of the Asthme et Allergies (Asthma and Allergies) organization, says he is increasingly prescribing desensitization treatments to his patients with pollen allergies. “I offer them more than before since there are strong chances that the seasons will remain very intense,” he explained. The doctor also warned about the risks of cross-food allergies: “prolonged exposure to the PR 10 protein, which is present in pollens, can create food reactions to all fruits after a while. It is on the rise among children.”
According to Samuel Monnier of the RNSA, risk reduction will also involve controlling the spread of ragweed and reducing the presence of allergenic species, planted in great numbers in cities. At the height of the pollen season, Monnier recommended that allergy sufferers brush their hair regularly, avoid drying laundry outdoors, air out rooms very early in the morning or late at night, and consult the allergy-pollen bulletins.