Itchy eyes and irritated skin. Sneeze after sneeze, each one more watery than the last. Allergy season is well underway. In Paris, birch trees get the ball rolling in March, and are soon joined by plane trees and lindens. According to the Paris mayor’s office, around 40 percent of the 200,000-odd trees in the city’s parks and lining its world-renowned boulevards have a “high allergenic potential”. Outside the French capital, Melbourne, Canberra, Tokyo and London are among the most hay fever-prone cities in the world. And unfortunately, allergic reactions to pollen is a problem that seems only likely to worsen. According to a 2016 report by the World Allergy Organisation, between 12 and 40 percent of the world’s population has seasonal allergies, depending on location, with Oceania topping the chart. The same report recorded an increase in the prevalence of pollen allergies from previous years in almost all regions. Another study conducted across 17 European countries found that 71 percent experienced an increase in their total pollen load, while 65 percent were experiencing longer pollen seasons mostly due to climate change. "Pollen plays a crucial role in the reproduction of plants,” says Gilles Oliver, an engineer at the National Aerobiological Surveillance Network, an organisation monitoring pollen in France. Although important, pollen can be recognised as an aggressor by our immune system if we’re not exposed to it enough. “That’s why people who grow up in the countryside are less allergic than city dwellers, at least in theory,” says Oliver. This is one of the many hypotheses researchers have for why pollen allergies are on the rise globally. More and more people are moving to cities, and the United Nations estimates that 68 percent of the world population will live in urban areas by 2050. At the same time, many cities are becoming greener, as urban planners increasingly value the impact of green areas on people’s mental and physical health. But looking more closely, urbanisation alone cannot be the culprit. In fact, urbanisation rates have only significantly spiked in Asia and Africa, while remaining mostly stable in all other continents – especially in Oceania, the most pollen allergy-prone continent – over the last half-decade. Oliver says another possible explanation could be linked to modern hygiene practices. “We clean too much”, he explains. “We are no longer used to coming into contact with allergens, which means our body recognises some things as enemies when it shouldn’t.” Although over-cleaning could be making things worse, Oliver thinks the main cause of the increase of allergies in France is likely air pollution. “It does two things”, Oliver said. “If you have allergies, it weakens your respiratory tract so you can get ill more easily. It also breaks up the pollen particles in the air, which allows them to penetrate deeper in our respiratory systems.” Pollution interacts with pollen in multiple ways, especially when it comes to CO2, which represents 76 percent of all human greenhouse gas emissions. “Trees need this gas for photosynthesis, a process that allows them to live and grow,” Oliver says. “But when the proportion of this CO2 in the air increases, plants grow faster and produce more pollen.” And since CO2 levels have been steadily on the rise since the 1950s, breaking all records in April of this year, it’s likely that our seasonal allergy problem is here to stay. Climate change aside, some of our gardening choices have also made things worse. For instance, landscapers often prefer planting male trees because they don’t shed seeds or fruits that need to be cleared, a phenomenon dubbed “botanical sexism” in the 1994 Yearbook of Agriculture. The problem is, male trees also tend to produce more allergenic pollen. On top of that, city planners have been choosing to plant certain types of trees because of their aesthetic value, not their impact on allergies. “For example, we plant birch trees because they are pretty,” Oliver says. But a 2019 study determined birch pollen is actually one of the main causes of allergies in the northern hemisphere. "Fortunately, it is still possible to control some of this urban pollen,” says Mathilde Renard, an agricultural engineer at the Environmental Department of the Paris City Hall. One of their main strategies is to diversify the species planted in the city, because most people are only allergic to the pollen of some trees when it’s above a certain concentration. Currently, more than 160 species are being used in the city’s replanting efforts, Renard says. “The mayor of Paris has also forbidden the planting of highly allergenic species - including, for instance, birches - in sensitive areas like those near schools or nurseries,” she adds. Allergy advocacy groups are also promoting the planting of low pollen trees like cedars and mulberries. Otherwise, things are getting pretty high-tech in the fight against pollen. Paris has set up a monitoring project called “Sentinel Pollinarium”, intended to anticipate big pollen waves three weeks in advance. Online, you can also find a map of Europe that alerts you as to which areas are the most affected by different kinds of pollen in real-time, so you can plan your travels to avoid potential allergic issues. Unfortunately, there’s not much you can do about allergies besides trying to manage them. Next time you find yourself cursing to the wind, remember: we have no one to blame but ourselves. Source
