Indoor airborne allergens
Indoor airborne allergens are particles present in indoor environments that can trigger allergic reactions or exacerbate respiratory conditions such as asthma.
Applies to England
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Topic: environmental exposures
Air-related exposure: airborne allergens
Part of: learning about airborne allergens
Key resources for indoor airborne allergens:
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Indoor airborne allergens
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Outdoor airborne allergens
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About indoor airborne allergens
Indoor airborne allergens are protein-based particles present in indoor environments that can trigger allergic reactions or exacerbate respiratory conditions such as asthma. Indoor bioaerosols are airborne particles like pollen and fungal spores. They come from poor ventilation, outdoor particles entering through windows, and fungi growth. Everyday activities like cleaning, moving around, and having pets can stir up allergens, while dust mites are another common source. Since people in Western countries spend the majority of their time indoors, these bioaerosols can significantly affect indoor air quality, contributing up to 34% of indoor air pollution (1). Exposure to these indoor pollutants can lead to various health issues, including allergic reactions, exacerbation of asthma and respiratory infections.
Common indoor allergens
Mould spores: mould is a fungus that thrives in damp, poorly ventilated spaces like bathrooms and releases airborne spores that can trigger asthma. It is often caused by leaks, condensation, poor heating, or inadequate ventilation (2, 3).
House dust mites: these microscopic organisms thrive in warm, humid environments and are commonly found in household dust, particularly in bedding, carpets, and upholstered furniture (4).
Pet dander: are proteins found in the skin flakes, urine, and saliva of pets, like cats and dogs, that can become airborne and cause allergic reactions.
There are some respiratory irritants that are not protein-based and are therefore not airborne allergens, but they can still pre-dispose someone to developing an allergy or to experience allergic exacerbation.
Volatile Organic Compounds (VOCs): these are emitted from various household products, including paints, cleaning agents, and air fresheners (5).
Particulate Matter (PM): indoor activities such as cooking, smoking, or using open solid-fuel fireplaces can release fine particles into the air which can irritate the airways and worsen health effects (6).
Climate change and indoor air quality
As the climate changes in the UK, older buildings can become less climate resilient impacting the health and comfort of the people who occupy them. This can be through changes to:
- Outdoor environmental conditions including changes to temperature, humidity, rainfall, and atmospheric levels of CO2 are likely to affect the species distribution and growth rates
- Climate events such as more frequent and severe heatwaves, wildfires, severe storms, and increases in outdoor ozone levels and outdoor pollen can also change allergen levels and potency
- Energy efficiency measures and adaptation measures, like the provision of mechanical ventilation to address thermal comfort, can have unintended consequences for indoor environmental quality, for example if mechanical ventilation is poorly installed it can worsen air quality
- Occupant behaviour, including indoor activities, the use of windows and mechanical ventilation
Interventions for indoor air quality
The following measures can be taken to maintain good indoor air quality and protect against airborne allergens:
- improve ventilation to remove additional moisture which can otherwise lead to damp and mould issues - more tips for reducing damp and mould can be found in this resource from National Energy Action, and more detailed advice including the responsibilities landlords have can be found here: Understanding and addressing the health risks of damp and mould in the home
- active air cleaning - use filters designed to reduce particulate matter and bioaerosols
- consider plants - the impact of house plants likely depends on species, root area, soil type, and foliage surface area - some studies show that house plants can have a positive impact on the removal of particulate matter, but other studies showed no improvement
- change behaviours - regular cleaning and minimising the use of products that emit harmful substances can reduce particulate matter and bioaerosols - occupants refraining from smoking and vaping indoors, and from using solid-fuel fires or free-standing gas heaters also helps to improve indoor air quality (7, 8)
Those who are most at risk from biological contaminants in indoor air are children (including during the prenatal period), and people with pre-existing conditions affecting the respiratory or immune systems.
For more advice on how to manage indoor allergens see the interactive ‘Allergy house’ tool from Allergy UK.
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, ‘Adverse Weather and Health Plan: Supporting evidence’ 2024 (viewed on 25 March 2025)
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Royal Borough of Kensington and Chelsea, ‘Taking Action on Asthma’ (viewed on 25 March 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 March 2025)
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UK Health Security Agency. ‘Health Effects of Climate Change Chapter 5: Impact of climate change policies on indoor environmental quality and health in UK housing’ 2012 (viewed on 18 March 2025)
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Salford City Council, ‘Indoor Air Quality’ (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 March 2025)
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Clark SN, Lam HCY, Goode EJ, Marczylo EL, Exley KS, Dimitroulopoulou, ‘The Burden of Respiratory Disease from Formaldehyde, Damp and Mould in English Housing’ Environments 2023: Volume 10(8) (viewed on 18 March 2025)