People assume they are allergic to dust – more likely is that they are allergic to dust mites (HDM). These are microscopic, and tend to reside in fabrics in the home esp bedding, carpets, sofas. So your house can be spotless but still be full of mites!
There are a number of different house dust mite species – most are Dermatophagoides (“skin eating”…), D. farinae is the American type, D. pteronyssinus is the European one.
HDM allergy is common in atopic individuals, contributing to eczema, rhinoconjunctivitis and asthma. Eczema usually comes first, but sensitisation (usually develops in young children) seems to predict development of asthma persisting into school age!
Although common, it doesn’t tend to cause immediate reactions, the way cat/dog does, probably because mites don’t fly – so exposure only caused when surfaces disturbed or if skin/nose/mouth/eyes in direct contact. But inflammation may be chronic, from brief, low quantity, frequent exposure. So even with avoidance/ reduction measures, it can take months to see the benefit…
There is cross-sensitivity with shellfish allergy but not fish allergy.
In some parts of the world, mouse and cockroach allergies more of an issue.
Lots of different allergens identified. der p 1 and 2 are major allergens in mite faeces, in kids with eczema various other allergens found in mite bodies also important. Mite faeces are the most important cause of sensitisation. Composition of skin prick solutions seems to vary…
Avoidance/reduction
Allergy UK has an advice leaflet with different measures for reducing levels of HDM in the home. Evidence however is that this is difficult to do and rarely seems to have any significant clinical effect! So no point in doing piecemeal, certainly.
Dust mites need high humidity to get water, so high altitude and air conditioning suppresses them. They also like temperatures over 20deg. They are photophobic so hide deep in fabrics.
Get rid of carpets, curtains, excess cushions/pillow/throws, move soft toys off bed.
Wash bedding at 60, or tumble dry! Soft toys go in the freezer overnight once a month (in a bag, obviously, to avoid collecting smells). Protective covers for mattresses and hypoallergenic bedding materials.
Some vacuum cleaners are better than others (in theory) eg with HEPMA filter. Allergy UK approves products (but only if company pay, of course). But the mechanical action of cleaning (plus moving furniture, changing beds etc) can whip particles up into the air (as can emptying the contents of the cleaner) so best done when kids are out, and wait 20 minutes before letting them back in… Cleaning and replacing filters important too.
Vacuuming alone resulted in a significant reduction in carpet house dust mite allergen concentration and load. Levels approached pretreatment values by 4 weeks posttreatment in the intensive vacuuming group, whereas combination of dry steam cleaning plus vacuuming lasted up to 8 weeks.
You can also use a steam cleaner on a mattress!
Evidence for air purifiers is mixed. If placed on carpet, they can actually disturb more allergen than they remove! You need to close doors and windows of course. Unfortunately the best ones tend to be big, expensive and noisy, and price does not mean good quality. Plus you have to remember to replace the filters. The cheapest Which? recommended one (the Electriq EAP500HC) costs over £200.
In PAXAMA study in the NW England (kids with a history of wheeze requiring a visit to hospital), impermeable covers (blinded!) halved risk of having an emergency hospital attendance over the next year. [Murray 2017] Maximum benefit was seen in under 11yrs, mono-sensitized to mite, living in nonsmoking households, and requiring more ICS.
[JACI 2018]Treatment
Systematic review found good evidence of benefit for eczema with immunotherapy against house dust mite, with subcut immunotherapy superior to sublingual. [Journal of Allergy & Clinical Immunology. 151(1):147-158, 2023 PMID 36191689]
Evidence for immunotherapy for allergic rhinitis, at least in adults… Treatment effect from 14 weeks, so not rapid…
No evidence for asthma… although research into whether HDM immunotherapy might prevent.
Acarizax is sublingual therapy (derived from D pteronyssinus and D farinae), indicated in adolescents (12-17 years) as well as adults diagnosed by clinical history and a positive test of house dust mite sensitisation (skin prick test and/or specific IgE) with persistent moderate to severe house dust mite allergic rhinitis despite use of symptom-relieving medication. £80 a month on NHS, has not been submitted to Scottish Medicines Consortium so currently not recommended.
International treatment guidelines refer to a treatment period of 3 years for allergy immunotherapy to achieve disease modification. Efficacy data is available for 18 months of treatment with ACARIZAX in adults; no data is available for 3 years of treatment. If no benefit in first year, no indication to continue.
First dose should be observed and the patient monitored for at least 30 minutes.
Place under the tongue, avoid swallowing for 1 minute, avoid food/drink for 5 minutes.
Contraindications are FEV1 <70% of predicted value despite treatment, or severe asthma exacerbation within the last 3 months.
If oral ulceration, postpone treatment.
Eosinophilic oesophagitis has been reported.