Climate change (particularly rising temperatures and carbon dioxide levels), urbanization and pollution led to the increase of ragweed biomass, length of pollen season and atmospheric pollen counts, while current forecasts show an upward trend in the future (Fig. 1). These factors play and will continue to play a major role in the increasing burden generated by ragweed sensitization for people living in affected areas.
The most prevalent species is A. artemisiifolia (common or short ragweed), which is also clinically the most relevant for its high potential to cause allergic sensitization (Fig. 2). Ragweed flowers between June and October. A single ragweed plant is estimated to produce a billion pollen grains during a season. Ragweed pollen can be transported over great distances, while trade and traffic globalization have been identified as the most important factors for ragweed distribution. Ragweed pollen has been identified at great distances, of more than 600 km offshore and over 3 km up in the air.