Bad news for city dwellers with hay fever, research suggests trees in urban areas make hay fever symptoms worse than in rural locations.

Research led by the University of Krakow shows that pollution found in large cities increases the potency of pollen grains in the air.

Past studies had highlighted the role that pollutants from vehicles and dust play in spreading pollen. The grains stick to the particles and remain airborne much longer than they naturally would.

This new study shows that city pollen is more potent as an allergen since trees are under more stress.

When pollution reaches the trees, they release stress proteins as a form of protection. One of these is known as Bet v1, an aggressive form of birch tree pollen.

Significantly higher quantities of Bet v1 was recorded by the team in silver birch trees in cities compared to the countryside in Poland.

While the same tests were not conducted on other common sources of aggravating tree pollen, such as hazel or alder trees, it is thought that results would be similar.

Pollen season in the UK and Ireland typically runs from February, with tree pollen, through to September with pollen from weeds. Although some studies suggest the pollen season is extending due to warming temperatures.

If you suffer from hay fever, be sure to check out the daily pollen counts with our pollen feature.