Study: Pollen levels vary significantly from one street to another

NEWS

POLICY & LEGAL

Heleen Kommers, Tuesday 4 August 2026

78 sec

Smarter choices in public green spaces can reduce exposure to allergenic pollen

People with hay fever may inhale significantly more pollen in one street than just a few streets away. This is the conclusion of a study by Leiden University of Applied Sciences. According to the researchers, the design of public green spaces plays a key role. Municipalities can reduce exposure to allergenic pollen by making more informed decisions about which species are planted and where.

Alnus (alder) is one of the earliest causes of hay fever, releasing allergenic pollen through wind dispersal.

For one year, pollen concentrations were measured twice a week at street level throughout the city of Leiden. Students walked through the city carrying portable "pollen sniffers." The collected pollen samples were subsequently analysed using microscopy and DNA analysis. This enabled the researchers to determine not only the amount of pollen present, but also the plant species from which it originated.

Pollen from public green spaces

The measurements show that pollen concentrations vary considerably across different parts of the city. Of the 322 plant species identified, 104 were classified as allergenic. Only six of these were garden plants. Most allergenic pollen originated from trees, grasses and other vegetation growing in public green spaces.

Pollen concentrations can vary considerably even within the same city

Another striking finding was that tree pollen was detected well beyond the normal flowering season. Birch pollen, for example, was still found in December. This suggests that people may continue to be exposed to allergenic tree pollen later in the year than previously assumed.

Species selection makes a difference

According to the researchers, municipalities can reduce pollen exposure by considering the allergenic properties of trees and other vegetation when planning new plantings. Choosing less allergenic species, particularly in heavily used locations such as schoolyards, public squares and popular walking and cycling routes, could deliver significant public health benefits.

The researchers also suggest that replacing lawns with non-allergenic herbaceous vegetation could help reduce grass pollen levels.

Careful species selection can reduce exposure to allergenic pollen

Tools for municipalities

To support municipalities in selecting suitable tree species, the researchers point to existing tools such as the Tree Allergenicity Compass. This tool enables designers and green space managers to take the potential impact of allergenic pollen into account when planning and managing public green spaces.

The design of public green spaces has a direct impact on local allergenic pollen levels

This article was previously published on 4 August 2026 on the Stad + Groen website.

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