Hayfever in the UK Extends to Autumn Months

by Kaylee Anderson

Hayfever is one of the most common allergic conditions, affecting as many as 10 million people in the United Kingdom. It is most well-known to be triggered by ragweeds in the United States and by grasses in the UK. Ragweeds were introduced to Europe in the 19th century, rapidly spreading by 1940.

It is believed that the threshold for clinical symptoms of hayfever is as low as 1-3 ragweed pollen grains/m3, which is significantly lower than other well-known pollen allergens, like grass and birch.

Ragweed is rarely included in UK pollen counts, however in 2014, an usually high concentration of ragweed pollen was observed at Leicester, the center of England. The purpose of this study was to examine whether this observation was an isolated event or if it is the start of a trend that hayfever season will extend into autumn as a result of climate change.

The average concentrations of ragweed pollen grains per day were measured using atmospheric spore traps and microscopic analysis. Thorough the comparison of 44 years of pollen data from the months of June through September, the authors speculate that the main ragweed pollen season is mid-August to the end of September.

The naturalization of ragweed in the UK is of high health concern to the allergic population. It is believed that ragweed seed production occurs in October and early November, implying that a long-lasting autumn is crucial to seed maturation and therefore, limits its distribution northward to colder climates. However, with climate change, there are predictions that ragweed will extend farther north and east to Scandinavian countries and Britain. Additionally, it was found that 2014 had one of the warmest autumns, behind 2006 and 2011, suggesting the UK may be moving towards the type of climate that would allow ragweed to naturalize.

If climate changes proceed and the spread of ragweed continues, hayfever will be a serious concern in the autumn months, when hayfever is believed to be over.


Pashley, C. H., Satchwell, J. and Edwards, R. E. (2015), Ragweed pollen: is climate change creating a new aeroallergen problem in the UK?. Clin Exp Allergy, 45: 1262–1265. doi:10.1111/cea.12572


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