「经济学人」Is your hay fever getting worse?

Climate change could be to blame

APRIL WAS the cruellest month. Just as the blossoms arrived, John Bostock found himself struck by “an unusual train of symptoms”. First came an “acute itching and smarting” around the eyes. Then came the sneezing.

The “periodical affection” that he described to the London Medico-Chirurgical Society in 1819 is now known as allergic rhinitis or, more commonly, hay fever. It is a condition in which the immune system reacts to airborne allergens, like pollen, by releasing histamine, an inflammatory chemical.

Considered rare a few centuries ago, it is now extremely common—estimated to affect one in five people in most industrialised countries, and up to two in five in some sensitive places, including Japan. Although rates are no longer increasing as fast as they once were, says Adam Fox of King’s College London, sufferers now seem to be sneezing for an increasingly long time each year.

Urbanisation may play a role: a study published in 2023 by Ann Gledson of the University of Manchester and colleagues found that seasonal allergy symptoms are significantly worse for city-dwellers. The exact cause is unclear, but poor air quality might either increase the protein content of grains or else heighten people’s immune response.

Climate change could also be to blame. Research conducted by Beverley Adams-Groom of the University of Worcester, who produces pollen forecasts for Britain’s national weather service, has shown that warmer springs in Britain prompt the main grass-pollen season (which normally runs from March to May) to begin earlier. Indeed, some tree species are now releasing pollen as early as January.

These trends are expected to continue in the coming decade, even if the extent to which they do will depend on the level of warming, and will vary by species and region. Warmer climates in central Europe and North America, for instance, will contribute to the spread of ragweed, a highly allergenic species that can require just one pollen grain per cubic metre of air to cause a reaction. Most species need more than ten. Extreme weather such as heatwaves and heavy rain can also decrease pollen production and dispersal.

Pity hay-fever sufferers, for it will be difficult to do much about their sneezing. One approach is to remove concentrations of allergenic species in cities, as Japan is doing. Its government plans to replace 20% of the country’s human-planted cedars with less allergenic trees over the next decade, roughly equivalent to cutting down 70,000 hectares a year—a drastic solution that has not been adopted elsewhere.

At least antihistamines and nasal sprays are generally able to counter symptoms. A study conducted by HAL Allergy, a Dutch pharmaceutical company, showed that new desensitisation treatments, which require a dose of the allergen to be placed under the tongue each day, can reduce symptoms by 32% relative to a placebo. Any such advance is welcome: a study led by Simon Sobstad Bensnes of the Norwegian University of Science and Technology suggests that on days with high pollen counts, which often coincide with exams, one in ten pupils with hay fever drops a grade.

Alternatively, consider the original remedy trialled by Dr Bostock. After years of sniffling, the good doctor resorted to relocating periodically to the blustery seaside town of Ramsgate, where he “nearly” managed to escape his affliction. Bless him. (May 2nd 2025)

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