Common UK Allergens. What You Are Actually Breathing
Understanding what triggers your allergies helps you choose the right purifier and set expectations for what it can and cannot do. Here is a breakdown of the most common indoor allergens in UK homes, their particle sizes, and how effectively air purifiers handle each one.
Pollen. The Seasonal Menace
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Tree Pollen
Birch, oak, plane. Late February to May. First wave of the season.
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Grass Pollen
Affects 95% of hay fever sufferers. Peaks May to July. Most common trigger.
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Weed Pollen
Nettle, dock, mugwort. June to September. Final wave of the season.
Pollen grains range from 10 to 100 microns — relatively large particles that all HEPA filters capture effectively. However, pollen also fragments into smaller sub-pollen particles (SPP) as small as 0.5 microns, especially after thunderstorms (hence the phenomenon of "thunderstorm asthma"). These fragments carry the same allergenic proteins but penetrate deeper into the lungs. HEPA H13 captures these fragments at 99.97% efficiency. The Philips NanoProtect filter captures them at an even higher rate.
Practical tip: during pollen season, keep windows closed from 7 AM to 10 AM and 5 PM to 7 PM when pollen counts peak. Run your purifier on a higher setting during these hours. Change your clothes when you come home, and shower before bed to remove pollen from your hair. Your air purifier handles the rest.
Dust Mites. The Year-Round Trigger
House dust mites (Dermatophagoides pteronyssinus) are microscopic arachnids that feed on human skin cells. They thrive in humid, warm environments, exactly the conditions found in UK bedding, carpets, and upholstered furniture. A single mattress can host between 100,000 and 10 million mites. The allergenic proteins (Der p 1 and Der p 2) are found in mite droppings, which are 10-20 microns in size.
Air purifiers capture airborne dust mite allergens effectively, but the majority of these particles are in bedding and soft furnishings rather than in the air. An air purifier works best when combined with dust mite-proof mattress and pillow encasements, weekly bedding washes at 60°C, and regular vacuuming with a HEPA-filtered vacuum cleaner. For comprehensive dust management, see our air purifier for dust guide.
Pet Allergens — Cats Are Worse Than Dogs
Cat allergen (Fel d 1) is produced in cat saliva, sebaceous glands, and skin. When a cat grooms itself, Fel d 1 dries on the fur and becomes airborne as ultrafine particles (1-5 microns). These particles are small enough to stay suspended in the air for hours and are incredibly sticky. They adhere to walls, clothing, and soft furnishings. Fel d 1 has been found in homes that have never had a cat, carried in on visitors' clothing.
Dog allergen (Can f 1) behaves similarly but is generally found in larger particles (5-20 microns) that settle faster. This makes dog allergens somewhat easier for air purifiers to manage, as the particles spend less time airborne. However, a boisterous dog that shakes its coat regularly can re-aerosolise settled allergens continuously.
Both allergens are captured effectively by HEPA H13 filters. The Philips NanoProtect is particularly effective against the smallest Fel d 1 particles. For dedicated pet allergen strategies, visit our pet air purifier guide.
Mould Spores. The Damp British Problem
UK homes are particularly prone to mould due to our damp climate, ageing housing stock, and the trend toward airtight energy-efficient buildings that trap moisture. Mould spores range from 2 to 20 microns, well within HEPA capture range. Common indoor moulds include Aspergillus, Cladosporium, and Penicillium, all of which produce allergenic spores year-round but peak in autumn and winter.
An air purifier removes airborne spores but does not address the root cause of mould growth, which is excess moisture. If you have visible mould, you need a dehumidifier to bring humidity below 50%, adequate ventilation, and professional mould removal if the area exceeds 1 m². An air purifier then prevents spores from the remaining mould growth from reaching your lungs while you address the underlying damp issue.
Our Allergy Testing Methodology
For pollen testing, we conducted trials during the May-July 2025 grass pollen season. Each purifier ran for 24 hours in a 25 m² living room with the windows closed. We used a Dylos DC1100 Pro particle counter to measure total airborne particle concentrations at 0.5+ microns (which includes pollen and pollen fragments) and compared readings with and without each purifier running.
For dust mite allergen testing, we used Acarex immunoassay test strips to measure Der p 1 concentrations on mattress surfaces before and after running each purifier in a sealed bedroom for 8 hours. Airborne dust mite allergen levels were measured with the particle counter at the 10+ micron range.
The Philips AC2939 consistently delivered the best allergen reduction across all tests, followed closely by the Levoit Core 400S (which compensates for its slightly less advanced filter with a higher CADR). For most allergy sufferers, either model will provide significant symptom relief when run continuously.
