Almost all of mainland France is classified as having a high allergic risk by the National Aerobiological Surveillance Network (RNSA) The maximum alert over a large part of the territory applies to birch pollen, “very allergenic and very abundant” The pollen season for this tree, very present around forests but also in many green spaces, began at the end of March, with the highest concentrations expected "during beautiful sunny days" Temperatures will soar above seasonal norms this weekend, after a previous weekend already marked by heat records for the start of April. Grass pollens in particular are “increasing in strength from the South” and their quantities are ‘increasing and are already high’ The more exposure to these pollens, the more allergies develop within the population.
Rising temperatures lead to earlier pollen pollination and lengthen pollen seasons for species, such as birch, which it weakens and irritates the respiratory tract, which worsens the consequences of pollution.