If the pollen count hits 50 grains per cubic metre of air on a given day, how worried should you be? It depends entirely on which plant released them. Three taxa drive the bulk of clinically severe rhinitis in France and most of Europe.
Cypress (January - April)
The first big season of the year. Cypress pollen is dominant on the Mediterranean arc and in the Cote d'Azur. Its pollen grains are large (~30 micrometres) and highly allergenic: an RNSA level 3 (out of 5) is usually enough to trigger sneezing in sensitised patients.
Birch (March - May)
Birch is the most widespread "temperate" allergen in France. Its pollen cross-reacts with apple, hazelnut and pear proteins, which explains why some birch-allergic adults suddenly develop oral allergy syndrome in their 30s. The birch season is also the one that has drifted most noticeably earlier over the last three decades.
Ragweed (August - October)
Introduced from North America a century ago, common ragweed (Ambrosia artemisiifolia) is now established across the Rhone-Alpes and Burgundy regions. A single plant can release one billion pollen grains over a season, and exposure to just a few grains per cubic metre is enough to trigger symptoms in sensitised individuals.
How ClearSpot weighs them
Our pollen module pulls the RNSA weekly bulletin (RAEP index 0-5 per taxon) and the CAMS 0.1 deg forecasts. We tag a cell as "not clear" whenever:
- any of the three top allergens reaches RAEP >= 3 and
- the user opted in to "pollen" during onboarding.
Other allergens (grasses, plane tree, olive, parietaria) only flip the verdict when they reach RAEP >= 4, reflecting their lower clinical impact at moderate concentrations.