Reducing the burden of allergens

Air pollution remains the most important environmental threat to health, and despite considerable progress, it remains a major cause of ill health and premature death

The Royal College of Physicians report, ‘A Breath of Fresh Air,’ responding to the health challenges of modern air pollution, states that around 30,000 deaths a year (500 per week) are attributable to air pollution in the UK, and links air pollution to the onset of more than 700 health conditions.¹

While the report predominantly focuses on outdoor air pollution, it also notes that indoor air quality is a growing concern: people spend the majority of their time inside with few standards for pollutant concentrations.Air quality and health inequalities are linked as air pollution disproportionally affects those from a deprived background.

Inhaled allergens in indoor air trigger asthma and other allergic and non-allergic illnesses.Indoor allergens include house dust mites (HDM), dust, indoor moulds/fungi, animal saliva, urine (including rabbit urine), skin flakes/dander (including from both cats and dogs), and feathers. Non allergenic pollutants in the air can include wood burners, formaldehyde, volatile organic compounds (VOCs), tobacco smoke and smoke from heating and cooking or from burning candles.Household chemicals increase this load.

In addition to outdoor air pollution, outdoor allergenic triggers include tree pollen (birch, hazel and alder are particularly problematic), grass pollen and weed pollen.

Research has shown that the presence of an allergen, allergen sensitivity and rhinovirus makes child hospitalisation from asthma 20 times more likely.²

An individualised multifactor systematic exposure reduction approach alongside medication, taking into account seasonality and where a patient is throughout the day (home/school/office) has been shown to be an effective solution.This approach was shown to improve asthma outcomes in a 2004 study of children in urban areas in the US.³ Other ongoing programmes by US Public Health Departments have also indicated that significant healthcare cost savings can be achieved by this approach.⁴

REDUCING THE IMPACT OF ALLERGENS

House dust mites, dust, indoor mould and animal dander can be issues all year round. Tree pollen, including birch – which is particularly significant for individuals with asthma – typically appears for approximately one month during April. Hazel and alder pollen are present earlier, generally in January and February. Grass pollen is in the air between May to July.Weed and mould spores are common in August and September. Reducing year-round exposure to allergens and pollutants can also help to relieve rhinitis symptoms during pollen seasons.

Effective allergen and pollutant reduction can be achieved by the use of appropriate anti-dust mite bedding, a vacuum cleaner that has a HEPA filter which removes 99.97% particulate, and which retains and does not release dust.Damp dusting and minimising exposure to other individual significant triggers are also beneficial. Using air purifiers to ‘clean’ the air can also reduce exposure to viruses.

Anti-dust mite bedding has been shown to reduce hospitalisations in children with house dust mite allergy,⁵ and is recommended by both the 2019 NICE indoor air quality guideline and the 2020 Royal College of Paediatrics and Child Health (RCPCH) Report on Health Effects of Indoor Air on Children and Young People for those with respiratory allergies.^6,7

The RCPCH report also recommended that children with respiratory conditions, including asthma and rhinitis, should take steps to reduce exposure to allergens (from house dust mites, moulds and pets) to reduce symptoms and exacerbations.⁷

An influential Cochrane review, ‘Does controlling exposure to house dust mites improve asthma?’ which concluded avoidance should not be recommended by doctors, has since been flagged as ‘predating current reporting standards and methodological expectations and should not be used for clinical decision making’.⁸

The NHS England ‘National bundle of care for children and young people with asthma’⁹ requires every conversation about asthma to include information about indoor and outdoor air pollution, and provides templates for what triggers to look for in a home of a child with asthma to reduce the risk of an asthma attack.

In the most recent BTS/NICE/SIGN guideline (2024), sensitivity to house dust mite allergy is recommended as a key diagnostic test for asthma.¹⁰

Issues with indoor and outdoor air pollution, allergies and pets were also highlighted as common features in the November 2024 report on National Child Mortality Database Report on Asthma and Anaphylaxis.¹¹

Allergen/pollutant/viral exposure might also occur at school or at work, or other places a patient might be during the day or where they go during the holidays, so attention needs to be paid to exposures in those environments.

KEY TRIGGERS AND SUGGESTIONS ON REDUCING EXPOSURE

House dust mites

House dust mite (HDM) allergen is the most common sensitising allergen and most children with asthma or food allergy will also have this allergy.

Reduction of overnight house dust mite exposure by use of anti-dust mite bedding or washing bedding at 60 degrees is key due to the length of time spent in bed. Anti-dust mite bedding was shown by Manchester University to reduce the risk hospitalisations in children who are allergic to house dust mites.⁵

Other ways to reduce HDM allergen include:

• Using a high filtration high-efficiency particulate air (HEPA) vacuum cleaner with a disposable bag that avoids releasing dust and allergens back into the environment
• Reducing the number of soft toys/freezing them/washing at 60 degrees.
• Using a toy container to store soft toys.
• Reducing the number of cushions and soft furnishings
• Removing all the items on a surface before wet dusting
• Wet dusting high tops of cupboards, and radiators
• Using a brush down the back of the radiator to remove dust build up before the heating is turned on in the winter
• Removing dust from bookshelves and the tops of books, or keeping books inside cupboards, as books can harbour dust
• Vacuuming or washing curtains and fabric headboards on beds
• Wiping drop down blinds particularly on the side facing the window; removing dust frequently from the slats of venetian blinds; washing net curtains
• Using top bunk of a bunk bed to avoid the mites in the mattress on the upper bunk from falling on the child on the lower bunk

Note that wooden floors still retain dust as larger particles – particulate matter with a diameter of <10 µm (PM10) has been shown to bounce off the floor to desk height in classrooms.¹²

House dust mites are also found in fabric sofa covers so if possible, replacing sofas with leather effect or other impermeable material, or reducing the number of upholstered furniture items may be helpful. Alternatively, using a washable cover that does not trap dust may help.

HEPA air purifiers with high clean air delivery rates can also be effective in improving air quality by removal of allergenic and non-allergenic particulate and viruses from the air. The use of stand-alone air purifiers was shown to increase attendance in schools during the COVID-19 pandemic by 20%.¹³However, the range of a static HEPA filtration device will be limited, and therefore a HEPA vacuum cleaner with a disposable bag may be of more use over longer distances indoors.

Dust

The contents of settled dust is a source of pollutants, including particulate matters, biological pollutants (from house dust mites and other pests, pet allergens, mould and fungi), Semi Volatile Organic Compounds, pesticides, flame retardants, phthalates, and even peanut or other food allergenic proteins.¹⁴

The RCPCH Report noted that vacuum cleaning is one of the simplest methods for clearing dust and is particularly important for those who suffer from asthma.7 However, it is important to note that there is evidence that vacuum cleaners can release and re-suspend dust and allergens into the air, presenting an additional source of exposure for susceptible populations.¹⁵ This happens both through vacuuming disturbing the dust and through emissions from the vacuum cleaner.

If a patient reports sneezing when they are using a vacuum cleaner, it suggests that there may be an issue with the vacuum cleaner or that they can smell dust.

Which? laboratory tests showed some vacuum cleaners release almost as much dust as they pick up, while others retain more than 99% of small dust particles.¹⁶ As well as being required to display an energy label, stating how energy-efficient they are, all vacuum cleaners must show data about their cleaning performance and dust emissions.

Mould

The recommended level for humidity is between 40 and 60%.Hygrometers, small devices which measure humidity levels, are available for about £5.

A dehumidifier can help control dampness by keeping humidity at acceptable levels.

The 2020 NICE Indoor Air Quality guidelines¹⁷ encourage people to ensure rooms are well ventilated by opening windows or using extractor fans, especially when cooking, drying clothes inside, or using sprays, solvents, and paints.

Windows should be kept closed during periods of outdoor pollution, such as rush hour, and open at other times of day, unless filtered air is available.

The walls should be checked for mould and removed safely or professionally. Mould may be a particular problem in bedrooms with external walls, especially if insulation is inadequate, or in houses which have been flooded.

The RCPCH report recommends increasing ventilation during and after activities that produce pollutants or moisture, especially when using cleaning or cosmetic products, cooking, bathing, and painting, decorating or buying new furniture.⁷

Steam cleaners or other sources of water vapour can as affect humidity and promote mould and house dust mite allergen within the house so their use should be kept to a minimum.

The Allergy UK guide to mould in homes offers detailed information about mould found in residential environments.¹⁹

Cats and Dogs

The RCPCH report recommends avoiding direct exposure to pets if the child is sensitised to animal hair and dander.⁷

Animal skin, saliva and urine (cat, dog, rabbit, hamsters) can be a serious trigger for asthma in homes (and schools) and was mentioned in the recent NCMD Report.¹¹ Cat allergens are particularly potent, are difficult to eliminate from homes and may trigger asthma or anaphylaxis.

Cats and dogs should not be allowed into bedrooms and dogs should be bathed frequently.

The new London Asthma Friendly Schools guidance provides guidance on warm blooded animals in schools.¹⁹

Tree Pollen

Of the 2,500 UK plant species Allergy UK reports that only 13 commonly cause respiratory allergy.

The most problematic tree pollens are birch (in April), hazel (January/February) and alder (also in January/February). Others include hornbeam, ash, plane and lime.²⁰

These trees are often planted in school playgrounds and park areas so recognising the trees can be useful to enable avoidance at the appropriate times, when catkins are on the trees or the pollen is being blown around.Families and schools should be advised not to accept the free allergenic trees from tree planting organisations.

A child with asthma may experience worsened symptoms in April if an allergenic tree, such as silver birch, is planted near their home.

Grass Pollen

Grass pollen is in the air between May and July. Tips you can pass on to your patients to reduce exposure include:

• Keeping the grass short.
• Rubbing petroleum jelly around the nose.
• Showering and changing clothes on return home
• Wearing wrap-around sunglasses

Outdoor mould spores

Mould spores are in the air in August and September and can also trigger allergic reactions.As autumn approaches, care should be taken sitting around falling leaves which may trigger reactions from mould spores.

During winter, real Christmas trees can release mould spores indoors, which can cause allergic reactions. Using an artificial tree may help, but artificial trees should be dusted before setup to avoid dust exposure.

OTHER POLLUTANTS

Respiratory issues can also arise from exposure to non-allergenic chemical pollutants

Examples around the house may include chemical cleaning products, sprays, formaldehyde from MDF furniture, and paints.

Some tips to reduce exposure may include the following:

• Not using sprays, air fresheners or harsh chemicals
• Using the cooker hood when cooking
• Using back hobs when cooking
• Putting lids on pans
• Avoiding DIY and building work around people with asthma and small children
• Using low VOC materials and paints
• Avoiding wood burners

Outdoor air pollution

Exposure to outdoor air pollution should be reduced as much as possible. This can be a year-round issue, so advise patients/parents and carers to consult the official Pollution Forecast at https://uk-air.defra.gov.uk/forecasting/ (https://uk-air.defra.gov.uk/forecasting/) which provides a 5-day, detailed, air quality forecast. However, it should be noted that national levels are not currently within World Health Organization guidelines.

Finding less polluted ways to go to school or work may be helpful, as may reducing time spent outdoors during the rush hour.²¹

The University of Surrey has produced a book ‘Mitigating Exposure to traffic pollution in and around schools’. ²¹

Schools

The NHS Asthma Friendly Schools guidance has been recently updated with information on indoor and outdoor air pollution and how to reduce exposure to inhaled allergens, pollutants and viruses within the school environment.²⁰ This is part of the Asthma Friendly Schools Initiative whereby schools can obtain certification for their asthma policies and procedures.The NCMD recommends all schools adopt this guidance.¹¹

In September (Week 38) there is an asthma spike due to cold virus circulation among children returning to school.Watch out for the NHS #AskAboutAsthma campaign that relates to this spike.²²

• Airborne Allergy Action is a community interest company set up to raise awareness of the benefits of airborne allergen avoidance for asthma and other allergic illness. We are on Instagram @AirborneAllergy, and our website is at http://www.airborneallergyaction.org

Further information for healthcare professionals and patients

• Indoor Air Quality Working Party. Resources. https://theinsidestory.health/category/resources/
• Allergy UK. Living with an allergy. https://www.allergyuk.org/living-with-an-allergy/indoor-allergies/

References

1. Royal College of Physicians. A breath of fresh air – responding to the health challenges of modern air pollution; 2025 https://www.rcp.ac.uk/media/5r2kmmi4/rcp-full-report-a-breath-of-fresh-air-responding-to-the-health-challenges-of-modern-air-pollution.pdf
2. Murray CS, Poletti G, Kebadze T, et al. Study of modifiable risk factors for asthma exacerbations. Thorax 2006;61(5):376-8 https://pubmed.ncbi.nlm.nih.gov/16384881/
3. Morgan WJ, Crain EF, Gruchalla RS, et al. Results of a home-based environmental intervention among urban children with asthma. N Engl J Med 2004;351(11):1068-80. https://pubmed.ncbi.nlm.nih.gov/15356304/
4. 4.Alameda County Asthma Start Programme https://www.youtube.com/watch?v=KoQZS36CJzc
5. 5.Murray CS, Foden P, Sumner H, et al. Preventing severe asthma exacerbations in children: A randomised trial of mite impermeable bedcovers. Am J Resp Crit Care Med 2017;196(2):150-158
6. NICE NG149. Indoor air quality at home; 2020. https://www.nice.org.uk/guidance/ng149
7. RCPCH. The inside story: health effects of indoor air quality on children and young people; 2020. https://www.rcpch.ac.uk/sites/default/files/2020-01/the-inside-story-report_january-2020.pdf
8. Gøtzsche PC, Johansen HK. House dust mite control measures for asthma. Cochrane Database of Systematic Reviews 2008; 2:CD001187. https://www.cochrane.org/CD001187/AIRWAYS_does-controlling-exposure-house-dust-mites-improve-asthma
9. NHS England. The national bundle of care for children and young people with asthma; 2021 (updated 2022). https://www.england.nhs.uk/publication/national-bundle-of-care-for-children-and-young-people-with-asthma/
10. NICE NG245. Asthma: diagnosis, monitoring and chronic asthma management (BTS, NICE, SIGN); November 2024. https://www.nice.org.uk/guidance/ng245
11. National Child Mortality Database. Child deaths due to asthma or anaphylaxis; December 2024 https://www.ncmd.info/publications/child-deaths-asthma-anaphylaxis-allergy/
12. Kumar P, Hama S, Abbass RA, et al. Environmental quality in sixty primary and secondary school classrooms in London. J Build Engineer 2024;91: 109549 https://www.sciencedirect.com/science/article/pii/S2352710224011173
13. Wilson C. Schools cut covid-19 sick days by 20 per cent using HEPA air filters. NewScientist; 20 October 2023. https://www.newscientist.com/article/2398713-schools-cut-covid-19-sick-days-by-20-per-cent-using-hepa-air-filters/
14. Sheehan W, Brough H et al: Distribution of Peanut protein in school and home environments of inner-city children. J Allergy Clin Immunol 2017;140(6):1724-26
15. Knibbs LD et al: Vacuum cleaner emissions as a source of indoor exposure of airborne particles and bacteria. Environ Sci Technol 2012;46(1):534-42
16. Laughlin A. Best vaccum cleaners 2025: tested by experts for a tidy home. Which? 24 July 2025. https://www.which.co.uk/reviews/vacuum-cleaners/article/best-vacuum-cleaners-abpwO0z6wv1C
17. NICE NG149. Indoor air quality at home; 2020. https://www.nice.org.uk/guidance/ng149
18. Allergy UK. A Wellcome home for all: housing rights guide. https://heyzine.com/flip-book/469fe59dd2.html
19. NHS. London Asthma Friendly Schools Guide. https://www.transformationpartners.nhs.uk/wp-content/uploads/2025/07/7-Asthma-guide-2025-final.pdf
20. Herald J, Hume SC, Warner A. Tree planting, air quality, global warming and their exponential impact on allergic rhinitis and asthma, in Allergy UK. The walk to school. https://www.allergyuk.org/wp-content/uploads/2021/10/The_Walk_To_School_TH8A91_1_original.pdf
21. Global Centre for Clean Air Research. Mitigating Exposure to traffic pollution in and around schools. https://www.surrey.ac.uk/sites/default/files/2021-01/mitigating-childrens-exposure-to-traffic-pollution-english-version.pdf
22. NHS England London Clinical Networks. Asthma campaigns #AskAboutAsthma 2025. https://www.england.nhs.uk/london/london-clinical-networks/our-networks/london-babies-children-and-young-peoples-transformation-team/asthma/asthma-campaigns/