Those who are allergic to alder pollen are currently having a particularly difficult time: According to the German Weather Service, pollen from trees in large parts of Germany has a medium to high exposure intensity.But hazelnut bushes still spread their pollen abundantly.At the beginning of January, the pollen information service declared this year's allergy season open, a consequence of the very mild winter.Now read on with STERN PLUSWhat you really need to know: background, analysis & classification© G+J Medien GmbH