Airborne allergens - a quick guide
Airborne allergens are particles in the air, including fungal spores and pollutants, that can cause or worsen allergic reactions and respiratory conditions such as hay fever and asthma.
Applies to England
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Airborne allergens - a quick guide
About airborne allergens
The air we breathe contains billions of tiny particles from natural sources like fungi, bacteria and viruses, as well as from man-made sources like waste management and industrial farming (1). Airborne allergens, or aeroallergens, are particles in the air that can cause allergy symptoms, particularly in people with hay fever and asthma. They include plant pollen, fungal spores, mould, dust mites, and animal dander. Climate change is expected to affect the amount and potency of these allergens as organisms adapt to more extreme weather. When combined with pollution, airborne allergens can be made more potent (2).
Definitions
Air quality: air quality is the cleanliness of the air we breathe and indicates the level of pollutants present in the atmosphere.
Air pollution: when air quality is poor, pollutants in the air may be hazardous to people, particularly those with lung or heart conditions.
Bioaerosols: bioaerosols are airborne particles of biological origin, including bacteria, fungi, viruses, pollen and skin cells as well as man-made particles from processes like waste management and industrial farming. They are common in the air we breathe (1, 3).
Airborne allergens (aeroallergens): airborne allergens are airborne particles, including pollen and fungal spores. They can worsen allergies, and trigger hay fever and asthma. They are part of the wider group of bioaerosols. (2).
The main types of airborne allergens
Pollen
Common types in the UK are grass pollen, tree pollen (birch, alder, hazel, oak), and weed pollen (mugwort, ragweed).
The impact of climate change means that in the Midlands and further north and west, some tree pollen might have their first high pollen days earlier and some species are expected to have more severe seasons. Further south, more frequent and severe heat could place stress on trees and reduce pollen output and season duration. The first high pollen day for grass has been getting earlier in the year but this trend could be hampered by more frequent heatwaves. Pollen has also become more potent but this could decline from the 2030s with higher levels of warming.
Fungal spores and mould
Common types in the UK are Alternaria, Cladosporium, and Aspergillus.
The impact of climate change means that warmer and wetter conditions may lead to increased spore production and an earlier start to the fungal spore season (2).
References
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Goode EJ, Douglas P and Marczylo E, ‘Understanding the Public Health Implications of Bioaerosols’ Chemical Hazards and Poisons Report: issue 28 (viewed on 1 April 2025)
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UK Health Security Agency, ‘Health Effects of Climate Change Chapter 6: Outdoor airborne allergic pollen and fungal spores’ 2012 (viewed on 18 December 2024)
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University of Leicester Centre for Environmental Health and Sustainability, ‘Bioaerosols and Health’ (Viewed on 10 March 2025)