Pollen from trees, grasses and weeds are causing seasonal allergies for approximately one fifth of the Swiss population every year. A study now found that due to climate change, the pollen season has shifted substantially over the past 30 years in onset, duration and intensity. "For at least four allergenic species, the tree pollen season now starts earlier than 30 years ago—sometimes even before January," said Marloes Eeftens, Principal Investigator and Group Leader at Swiss TPH. "The duration and intensity of the pollen season have also increased for several species, meaning that allergic people not only suffer for a longer period of time but also react stronger to these higher concentrations."