It scratches the throat, it stings the eyes, it makes you sneeze… After the pollens of trees, like birch, the pollens of grasses, like wheat, are spreading over the whole of France in this mid-May . This season, which begins in spring and lasts until autumn, is synonymous with allergies (sometimes very serious) for around 20% of children and 30% of French adults. Franceinfo explains why this allergy season is aggravated by the climate crisis.
Because the pollen season will get longer
For the moment, the pollen season is rather regular, notes Samuel Monnier, communication manager of the National Aerobiological Surveillance Network (RNSA), asked by franceinfo. “It is sometimes a little earlier, but it is only a few days at the end of winter”, he remarks. It also happens that the pollen season plays extra time. This was the case in 2020, he notes. A heat episode “extremely remarkable” in September generated a peak in ragweed pollen production in mid-September, whereas it usually occurs in mid-August.
But Dina Kabirova, allergist in the 5th arrondissement of Paris, tells franceinfo that she has already noticed a relative lengthening of the pollen season, conducive to allergies. “Sometimes it starts at the end of January et ends at the beginning of October”she observes, specifying that the episodes causing peaks in consultations remain mainly “between March and July”.
Due to global warming, the lengthening of the pollen season will be especially important and visible at the end of the century, according to a study published in March in the journal Nature Communications. By 2100, this period could begin up to 40 days earlier, end 19 days later, and result in a 40% increase in pollen production. “Patients will be bothered longer, the effects will sometimes be more severe”, warns Dina Kabirova. Impossible for the specialist to detail more, because it depends on each patient and his lifestyle. However, she insists on this idea: “The longer an allergy lasts, the more it damages.”
Because plants with highly allergenic pollen move
With the temperatures warming up on the surface of the globe, plants or trees are gaining new territories, moving north, like the birches, already present in northern Europe and France. The phenomenon is also noted for plants usually more present in the South, like cypresses, which also cause many allergies.
The establishment of ragweed, an invasive exotic plant native to North America and highly allergenic, is also closely monitored. “We are starting to have ragweed allergies a little further north. As the climate changes, the environment changes and so do allergies”, commented on franceinfo the allergist Sophie Silcret-Grieu. Ambrosia is thus now present in Savoie, notes the RNSA, whereas it was not observed at all at altitude before.
However, this translation of plants is encountering obstacles. If the development of ambrosia worries in France, the RNSA notes that its conquest of the North is notably blocked by the “photoperiod”, the rhythm of alternation between day and night. If it proliferates in the South, ambrosia fails to produce seeds in the North, wrote the French journal of allergology in May 2021.
Because more pollens are produced and they are more allergenic
The rise in temperatures, linked to global warming, leads to a greater production of pollen from plants, emphasizes Samuel Monnier. This is the case for example of birch, studied by the National Observatory on the effects of global warming (Onerc). For this tree, responsible for many allergies from the north of France to the Auvergne-Rhône-Alpes region, “over more than thirty years, the amount of pollen increases at the same time as the temperature curve” in six towns in France, notes Samuel Monnier. “The change in temperatures has only led to an increase in the quantity of birch pollen emitted and therefore an increase in allergies”writes the observatory.
Carbon dioxide (CO2), an important greenhouse gas, whose global emissions have exploded due to human activities, has a significant impact on pollens. The increase in its concentration in the air encourages the growth of plants, which absorb this gas, with a double consequence: “More pollen is produced, pollen that is more allergenic”explains to franceinfo Samuel Monnier.
This observation was made in particular on ragweed. For this plant which causes many allergies, “the amount of allergens per pollen grain is correlated with the atmospheric concentration of CO2”wrote Marie Choël and Nicolas Visez, two scientists who are members of the Association for the Prevention of Atmospheric Pollution (APPA), in an article published in 2019 on the site The Conversation, referring to this study (in English) appeared the previous year.
Because air pollution weakens the airways and promotes the release of pollen
Global warming and air pollution are “intimately linked”, writes Public Health France. CO2 is not the only pollutant implicated. “Some of the air pollutants are also greenhouse gases and contribute to climate change, such as ozone for example”, explains the health agency. However, air pollution acts in several ways on allergies. “Pollution has a direct irritant effect on the respiratory tract and a facilitating effect for pollens”, explains allergist Dina Kabirova. Result : “Allergies happen more easily.” This phenomenon, the allergist observes him “a lot in town, especially for people who travel by motorbike or scooter, for example”.
The other effect of air pollution does not affect the human body, but the pollen grains. It attacks them, weakens their wall, allowing them to release more material. “A grain of pollen is a bit like a grain of pepper, there is a shell around it, called the exine, which is cracked by chemicals in the air. The grain releases therefore a greater quantity of allergenic substances”explained to France 3 Ile-de-France the allergist Patrick Rufin.
Because developing a first allergy opens the door to others
With global warming, the risk is both to see the number of allergic people increase and to observe a multiplication of allergies. LAllergist Sophie Silcret-Grieu described this vicious circle on franceinfo. “Birch pollen is allergenic, quite simply because it is very abundant, because birch trees have been planted massively and it is a pollen that is overrepresented in the northern half of Europe. It is for that makes you allergic to birch, but you have a big risk of becoming allergic to grass pollen, mugwort, cat, peanuts”, explained this specialist attached to the Center for asthma and allergies at the Trousseau Hospital in Paris. And to emphasize: “Allergic predisposition does not tell us what we will be allergic to, but simply makes us vulnerable to developing certain allergies.”
Faced with this aggravation of the situation for allergy sufferers and sensitive people, the RNSA provides some practical advice: ventilate the accommodation before and after sunset, rinse your hair before going to bed, avoid drying clothes in the outside, keep car windows closed, avoid sporting activities during peak pollen dispersal, follow your treatment or consult an allergist if this has not already been done. The network also points out that wearing a mask can also protect the airways, just as wearing glasses can protect the eyes, a sensitive mucous membrane for some people.