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A study published in The Lancet Planetary Health looks at the impact of nitrogen fertiliser on pollen allergies.
Dr Roy Neilson, Soil Ecologist, The James Hutton Institute, said:
“Daelemans et al. take a novel approach of pollen assessment in considering the impact of nitrogen fertiliser application on pollen burden. Using a paired design at 25 grassland sites within a region of Belgium, and based on two sampling periods during May, the authors report that nitrogen-enriched grasslands had a 6·2-fold increase in pollen compared with their unfertilised paired grassland.
“The results of the study arguably support the importance of species-specific grass pollen monitoring given that a subset of grass species may have disproportionate influence on respiratory health responses during peak grass pollen concentrations1. However, it is unclear how nitrogen driven increase in pollen will contribute to the predicted increase in pollen season severity by up to 60% due to a changing climate2.
“Peaks in abundance of pollen occur at different times during the summer across the UK3 thus, it is unclear whether sampling in a single month as the study of Daelemans et al. would have the same outcome across the entire pollen season. Moreover, unlike tree pollen, a recent study reported that grass (Poaceae) pollen seasons are neither becoming more severe nor longer in the UK4.
“Adoption of Regenerative Agricultural principles5 such as reducing synthetic inputs (e.g., inorganic nitrogen-based fertiliser) has potential to contribute to the mitigation of the outcomes reported by Daelemans et al.”
References:
1 Rowney, et al. (2021). Environmental DNA analysis reveals links between abundance and composition of airborne grass pollen and respiratory health. Current Biology, 31, 1-9.
2 Kurganskiy, et al. (2021). Predicting the severity of the grass pollen season and the effect of climate change in Northwest Europe. Science Advances, 7, eabd7658.
3 Brennan, et al. (2019). Grass allergy season defined by spatio-temporal shifts in airborne pollen biodiversity. Nature Ecology and Evolution, 3, 750-754.
4 Adams-Groom, B., Selby, K., Derrett, S., Frisk, C.A., Pashley, C.H., Satchwell, J., King, D., McKenzie, G., and Neilson, R. (2022). Pollen season trends as markers of climate change impact: Betula, Quercus and Poaceae. Science of the Total Environment, 831, 154882.
5 British Ecological Society (2025). Regenerative Agriculture in the UK: An Ecological Perspective. London, UK.
Dr Roberto Picetti, Assistant Professor, London School of Hygiene & Tropical Medicine (LSHTM) said:
“This study highlights the impact of nitrogen pollution on allergies, which is an under-recognised pathway affecting human health.
“These findings are relevant to the UK, where nitrogen pollution remains a concern both in agricultural areas and in cities, and is already linked to other environmental and health problems, including respiratory illness, biodiversity loss, and air and water quality degradation.
“It builds on well-established research which continues to find a link between high levels of nitrogen and changes in plant communities and pollen abundance, and to increased immune responses in individuals who are allergic to grass pollen.
“This is a high-quality study that adds valuable evidence to an important and emerging area of public health. The conclusions are well grounded in the data, do not overstate the implications, and make a compelling case for further research and policy attention. Although observational studies are not able to account for every possible variable, this research uses a range of scientific approaches, such as ecology, molecular analysis and immunological testing, to strengthen its conclusions.
“This study is a valuable step towards understanding and addressing the growing problem of pollen allergies and supports the case for more comprehensive environmental policies that consider both the health and ecological impacts of nitrogen pollution.
“By reducing nitrogen pollution, we could help protect biodiversity and lessen the severity of pollen allergies.”
(from our friends at SMC Spain) Dr José Gómez Rial, Head of the Immunology Department at the Complejo Hospitalario Universitario de Santiago de Compostela (CHUS), Servicio Gallego de Salud (SERGAS) (Spain), said:
“The study shows that nitrogen-enriched meadows produce up to six times more pollen than their unfertilised equivalents, and that this pollen has a greater capacity to activate immune cells in allergy sufferers, with a 5.1-fold increase in sensitivity in basophil activation tests and a 1.3-fold increase in specific immunoglobulin E (IgE) levels. Although the exact mechanism is not detailed in the article, it is plausible that excess nitrogen modifies the biochemical composition of pollen, increasing the quantity or proportion of allergenic proteins synthesised by the plant, which would enhance its capacity to activate the immune system.
“These findings have important implications for both ecology and health. On the one hand, they reveal that nitrogen pollution not only affects plant biodiversity but can also directly aggravate highly prevalent allergic diseases such as rhinitis or seasonal asthma. On the other hand, they emphasise the need to integrate public health into environmental policies: reducing nitrogen emissions and limiting the use of fertilisers would not only contribute to preserving ecosystems but could also reduce the burden of disease associated with respiratory allergies. The concept of One Health applies not only to human and animal health, but also to plant health and the environment”.
(from our friends at SMC Spain) Prof África González-Fernández, Researcher at CINBIO, Professor of Immunology at the University of Vigo (Spain), said:
“The experiment is well-reasoned, but they analyse few cases (25 people in rich areas and 25 in areas not enriched with fertilisers). It has not been done in other areas, and the in vitro trials were carried out with 20 subjects. There is a lack of healthy controls.
“There are studies from years ago on the increase in allergy and nitrogen fertilisers, as well as on NO2 levels and allergy. There is a lot of literature on the subject. Other studies have been carried out measuring IgE levels and they have included a basophil release test, which is currently used routinely in immunology laboratories in hospitals. They conclude that allergic patients recognise more proteins in the pollen of fertilised plants (enriched in nitrogen) than in those that are not fertilised, with more production of specific IgE and more release of mediators by basophils when exposed to fertilised pollen.
“The same authors wrote a review in 2023: Impact of environmental nitrogen pollution on pollen allergy: A scoping review. In Table 4 they describe the mechanisms by which NO2 would affect pollen and the allergic response.
“I see several limitations:
‘The impact of ecosystem nitrogen enrichment on pollen allergy: a cross-sectional paired comparison study’ by Robin Daelemans et al. was published in The Lancet Planetary Health at 23:30 UK time on Wednesday 16th April 2025.
Declared interests
Dr Roberto Picetti: No conflicts of interest to declare.
For all other experts, no reply to our request for DOIs was received.