Where the allergen actually is, why symptoms run all year rather than seasonally, and an honest account of which avoidance measures the evidence supports — which is fewer than most advice suggests.
What the allergen is
House dust mites are microscopic relatives of spiders that live in every home, feeding on the flakes of shed human skin that collect in bedding and soft furnishings. They are not parasites, they do not bite, and their presence is not a sign of a dirty house.
The allergen is not the mite. It is a set of proteins found chiefly in the mites' droppings, along with fragments of dead mites. Those particles are what the immune system reacts to. In someone sensitised to them, IgE antibodies against those proteins sit attached to mast cells in the lining of the nose and airways; when the particles are inhaled, they bind to that IgE and the mast cells release the histamine they are holding, which produces the symptoms. The underlying process is the same one that drives hay fever.
Where the allergen collects matters more than most advice acknowledges. Mites need warmth and moisture, and the richest source in any house is the bed — the mattress, pillows and duvet, which combine both along with a nightly supply of food. Carpets, upholstered furniture, curtains and soft toys are secondary reservoirs. Very little of the allergen is floating in the air at any given moment: the particles are relatively heavy and settle quickly once disturbed. That single fact explains why measures aimed at the air achieve less than measures aimed at the bed.
It is not seasonal
Unlike pollen, house dust mite is present all year, which is the most useful thing to know about it. Symptoms that run through the winter, or that never really stop, point to an indoor allergen rather than to pollen.
Older writing sometimes claims mite numbers peak in winter because of rain and melting snow. That is not how it works. Mites depend on humidity and warmth, and central heating through a British winter dries indoor air, which works against them. What does change in winter is exposure rather than population: windows stay shut, ventilation drops and people spend far more time indoors and in bed.
What it causes
Mite allergy typically produces perennial allergic rhinitis — a blocked or running nose, sneezing, and postnasal drip, often worst on waking because of the hours spent with the face against the richest allergen source in the house. Itchy, red eyes are common. It can worsen eczema.
Its most important association is with asthma. House dust mite is among the commonest allergic triggers for asthma in the UK, and that connection is the reason the avoidance question has been studied as much as it has.
Does avoiding it work?
This deserves an honest answer rather than a confident one, because the evidence is genuinely mixed, and most writing on the subject presents an exhausting programme of measures as though their value were settled.
Two things are reasonably clear. Avoidance does not prevent someone becoming allergic in the first place; sensitisation can follow quite short exposures. And whatever is done has to be sustained, because airway sensitivity takes months to settle even where exposure genuinely falls.
Beyond that, the literature disagrees. A large Cochrane review pooling 55 trials and more than 3,000 people with asthma found no benefit from either physical or chemical mite-control measures on symptoms, peak flow or medication use, and concluded that they could not be recommended. More recent reviews take a more favourable view, particularly for children with mite-driven asthma, where mattress and bedding encasings have reduced symptoms and inhaled steroid requirement in trials. Results in allergic rhinitis are less consistent: one large trial reduced measured allergen without producing clinical improvement.
The thread running through the more positive findings is that single measures in isolation achieve very little. Encasing a mattress while leaving everything else unchanged does not reduce total exposure enough to matter. Measures appear to work, where they work at all, as a combined and maintained effort concentrated on the bedroom.
The practical conclusion is not that avoidance is pointless, but that it is secondary. Treatment does more for most people than cleaning does, and anyone whose symptoms are significant should not be putting their effort into housework at the expense of getting the treatment right.
What is worth doing
Concentrate on the bed, and on humidity.
Encasings have the best evidence of any single measure, and their quality determines whether they do anything. The useful ones have a pore size small enough to block allergen particles, sealed seams and zips, and cover the mattress, pillows and duvet rather than the mattress alone. They are woven and breathable rather than plastic. They should be washed rarely, since washing degrades the barrier — the cover is there to separate the sleeper from the reservoir, not to be laundered weekly.
Wash the rest of the bedding at 60°C or above. Lower temperatures remove some allergen but do not kill mites. Tumble drying helps. This is the measure most often undermined in practice by a 40°C setting.
Keep indoor humidity down, somewhere below about 45 to 50 per cent relative humidity, which is the level at which mites begin to struggle. Ventilation, extractor fans and not drying washing indoors all help. Controlled studies of dehumidifiers have been inconsistent, so this is plausible and sensible rather than proven.
Soft toys that cannot be washed hot can be put in the freezer overnight, which kills mites, then washed to remove the allergen.
A vacuum cleaner with a good filter removes most allergen-carrying particles rather than redistributing them, which a poor one does.
What is not worth the effort
Several familiar recommendations do not hold up, and saying so saves people considerable trouble and expense.
Replacing carpets and curtains is not supported. Carpets and upholstery are genuine allergen reservoirs, but removing them has not been shown to improve symptoms, and it is an expensive intervention to undertake on that basis. Humidity is the better target.
Chemical mite killers have no controlled evidence of clinical benefit, and no individual product has been shown to reduce mite populations meaningfully.
Air filtration is of limited use here specifically, because mite allergen does not stay airborne — which is why air purifiers help least with the allergen they are most often bought for.
Wearing a mask to dust, adding bleach to the wash, and attempting to freeze a mattress are all measures that appear in older advice and can be set aside.
Treatment
A pharmacist can advise without an appointment. Non-sedating antihistamines — cetirizine, loratadine, fexofenadine, acrivastine — help with sneezing, itching and a running nose, and less with a blocked one. For a persistently blocked or runny nose, a steroid nasal spray is more effective and is the mainstay; since mite allergy is perennial, it is used continuously rather than seasonally, and it needs days to weeks of daily use before it is working properly.
Brand names are not a reliable guide, since the same brand can contain different active ingredients in different countries. The generic name in the small print is what to go by. The full range is covered under managing allergies.
Where asthma is part of the picture, it needs managing as asthma, with its own review, inhalers and written action plan, rather than being treated as an extension of the allergy. Inhaler treatment is not something to start or adjust on the strength of a general article.
Immunotherapy
House dust mite is one of the established indications for immunotherapy, which is the only treatment that changes the allergy itself. It is given over about three years, as injections or as a daily tablet dissolved under the tongue, and it is reached by GP referral to an allergy clinic.
It is worth raising where symptoms persist despite proper treatment, and current guidance suggests it should not be left too late: for mild symptoms, a reasonable approach is to try avoidance measures properly for six weeks or so and consider immunotherapy if nothing improves, while for moderate to severe symptoms it is considered alongside the measures rather than after them.
Getting it confirmed
Year-round indoor symptoms can come from mites, from animals, from mould, or from something that is not allergy at all, and the treatments differ. Testing read alongside the history is how they are distinguished — and a positive test on its own is not a diagnosis, which matters here more than most, given how much effort a mite diagnosis can prompt.
A GP visit is worth it where symptoms are not controlled by over-the-counter treatment, where sleep, work or school is affected, where asthma is involved, or where it is unclear what is causing them.
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