Hay fever and pollen

Hay fever is an allergic reaction that is caused by pollen from trees, grasses and herbaceous plants. When this pollen is dispersed by the wind, people with hay fever suffer from sneezing, red and itchy eyes and a stuffy nose.

Weather conditions determine when 'hay fever plants' flower and how much pollen they release into the atmosphere. Every year, the progression of hay fever symptoms can differ. The daily pollen concentration in the atmosphere in the Netherlands is measured by the Leiden University Medical Center (LUMC) and Elkerliek Hospital in Helmond.

As part of the Nature’s Calendar observation programme, secondary school students and volunteers keep track of when various hay fever plants begin flowering. The students who conduct observations are also involved with the GLOBE Programme, an international education programme on the environmental sciences established in 1995 by Al Gore.

Knowledge about hay fever is limited

Between 800,000 and 1.5 million people in the Netherlands suffer from hay fever. However, their knowledge about this allergy is often limited. For example, they do not understand why allergy symptoms occur, which plants cause symptoms and when the symptoms occur. They often mistakenly assume that they have a cold, and therefore do not take the correct medication. Hay fever medication can greatly reduce the severity of allergic reactions.


One plant species that is known world-wide for causing hay fever symptoms is Ambrosia. This species, which is an exotic in the Netherlands, produces large amounts of strongly allergenic pollen. Moreover, the plant flowers late in the year, so the hay fever season for people who are sensitive to Ambrosia can be up to two months longer. Ambrosia originated from North America and has become widespread in the Netherlands because its seeds are unintentionally present in birdseed and wildflower mixtures. By removing plants before they begin flowering, nuisance from the pollen can be prevented, and the species is less likely to spread.

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