House dust mite avoidance
Author: Dr R G Turner, Hospital Practitioner to the Paediatric Allergy Clinic, Basingstoke and North Hampshire Hospital
Date: Feb 2011
House dust is the major cause of allergy in persons with year long runny or blocked nose and/or sneezing. In addition to these allergic reactions, dust can trigger asthma, night coughs and irritant eyes and exacerbate eczema.
What is in house dust mites that causes allergies?
A speck of dust may contain fabric fibres, human skin bacteria, animal danders, pollen grains, mould spores, food particles and mites. Since 1964 it has been recognised that house dust mites cause the biggest problem. They feed off skin scales shed by humans and are the major allergen (allergy causing substance) in house dust. Nearly half of young asthma sufferers are allergic to mites and their asthma has been shown to improve in mite-free environments.
What are dust mites like?
Mites are members of the eight-legged Arachnid family. They cannot be seen without a microscope. They thrive in warm, humid conditions. They cannot survive when the humidity falls below 40% and so are very rare in dry, high altitude areas. Because they feed on skin scales, they love bedding, carpeting, upholstered furniture, clothing, closets and car seats.
They usually survive ordinary vacuuming because they burrow deep and are equipped with sucking pads on their feet.
People become allergic to the proteins in mite faecal pellets. As many as 3,000 mites have been counted in a gram of dust, although the average is probably nearer 200-500. Each mite produces 10-20 faecal particles per day. Their life cycle from egg to adult is 30 days. Each egg laying female mite can increase the population by 40-80 every six weeks.
Studies in London show that mite populations peak from December to March, i.e. times of high household humidity, although levels remain high from late summer onwards. The lowest allergen levels are in early summer, but even at these times mite sensitive persons can get symptoms because the mite faecal particles remain in the home.
There is a variation in the incidence of mite allergy with birth month: mite sensitisation is most likely in those born three months before the peaks in mite population.
Ducted air central heating systems stir up the problem by blowing around dust. Symptoms may be better in summer because more time is spent outdoors and the central heating is off.
How is an allergy to dust mites diagnosed?
By medical history and by skin testing: a positive reaction – a raised weal circled by redness – indicates allergy – the larger the weal the greater the allergy.
Once mite allergy is diagnosed, what can be done to help the symptoms?
Dust mites are very difficult to eradicate. Anti-dust programmes will reduce the number of mites, thereby reducing symptoms, but live mites are more difficult to remove by vacuuming than dead ones. Intensive vacuuming is needed to remove significant amounts of dust from carpets.
The home needs to be cleaned thoroughly on a regular basis with frequent vacuuming and dusting with a damp cloth. Ideally cleaning should be done while the dust sensitive person is out of the home. However, if a dust sensitive person has to do the cleaning, a suitable mask can be worn.
Although most vacuum cleaners have good suction, many do not have fine enough filtration to trap and retain mites. Ordinary cleaners may actually put more mites into the air. If you are very sensitive, therefore, it is important to use a cleaner that has been specially designed to deal with the problem. These types of vacuum cleaners are relatively expensive, but nevertheless may be worth it for the very sensitive person.
Mite allergens are very water-soluble. One product (Allerite) contains solvents and wetting agents and is intended for use with the VAX vacuum cleaner. This system has been shown to significantly reduce house dust mite allergens.
Acaricides are chemical agents that kill mites. Intensive and thorough vacuum cleaning of treated areas in order to remove the allergen pool of killed mites and their faecal material must follow their use. The results of published studies on the use of acaricides in the home do indicate some reduction in allergen concentration, but they are not effective as a sole measure. So far, the most trialled acaricides is ACAROSAN (Benzyl Benzoate). I do NOT recommend the use of these agents though because they may act as irritants and we do not know the long-term effects of them on the body.
Dust control in the bedroom
The highest concentrations of mites occur in the bedroom, especially in the mattress and bedding and on average we spend up to a third of our day there. Rather than pillows stuffed with feathers, down, kapok or foam rubber, use pillows stuffed with Dacron or other synthetic materials.
Mattresses, duvets and pillows should be enclosed in non-allergenic covers. These micro porous covers have been developed to allow the passage of water vapour whilst excluding mite allergens. Clinical studies show improvement in symptoms following the use of these covers.
In summer, take the mattress outside, then take the cover off and give it a good beating and replace the cover before bringing the mattress back inside.
Also, air duvets (with covers off) in sunlight as ultra-violet light is harmful to mites. They should also be made of materials such as Terylene. Pillows (and duvets) can be washed in the machine once a year – with cover removed.
Avoid padded fabric headboards, mites thrive in these, wooden types are better. Don’t let children use beds as a trampoline, as this disturbs the allergen in the mattress. Hang clothes in the wardrobe or put them in drawers using dust covers where possible. Stuffed animals can harbour mites, so eliminate them if possible, or at least wash them regularly or freeze them (see “Toys”). You should never let an allergic child sleep in the lower bunk of bunk beds. Do not hang dressing gowns on the back of the bedroom door, as they will collect dust there. (N.B. Only washing in a hot wash (over 60°) will kill mites).
Other dust prevention
Carpeting provides a breeding ground for mites. Eliminate them as far as possible – short pile rugs are preferable. Long pile carpets are a disaster. Steam cleaning is usually impracticable but will clear the allergens from the mites’ excreta. Don’t forget to clean under the bed regularly, as dust falls regularly through the mattress. It may be better to have a carpet under the bed, as this will trap the dust which can then be vacuumed, as dust blows off bare floors.
There is some evidence that artificial fibres may give rise to less airborne dust than woollen ones due to a higher static charge.
Should be lightweight as they are easier to clean and wash. Ideally they should be vacuumed regularly.
Should be of a simple, clean design, instead of ornately carved pieces. Older furniture stuffed with animal hair, kapok, feathers or foam is particularly bad. Venetian blinds just collect dust and are difficult to clean.
Should be able to be easily cleaned, certainly do not use dried flower arrangements and the like. Embossed wallpaper can be a dust trap; smooth, easy to clean wall finishes are best.
Collect dust, so should be damp dusted and vacuumed regularly.
Mites in children’s soft toys are effectively killed either by regular washing at high temperatures or leaving them in the freezer for 24 hours.
Besides carrying out dust avoidance, individuals allergic to dust should try to avoid contact with such inhalants as insect sprays, tobacco smoke and fresh paint or any high concentration of air pollutants.
There is evidence that built-in vacuuming systems reduce symptoms but these are much more expensive.
To supplement avoidance measures, certain medications may be prescribed that may relieve the irritating symptoms of allergic reactions. Antihistamines, corticosteroids and disodium cromoglycate are among the drugs available, depending on the severity and nature of the reaction.
Nose drops and sprays are frequently used by allergy sufferers without consulting their doctors, but all too often people become too dependent on this treatment and overuse it so that in the end the symptoms may be worsened rather than improved. Appropriate treatments will be discussed at your consultation.
If avoidance measures and medications do not control the symptoms of an allergy, immunotherapy may also be tried in certain cases. There are several methods currently used. Broadly, therapy comes in either high dose or low dose regimens. There are safety issues with the high dose regimens and efficacy issues with the low dose. These treatments can be fully discussed if appropriate for you.
Article written and supplied by Dr R.G. Turner. He is Hospital Practitioner to the Paediatric Allergy Clinic Basingstoke and North Hampshire Hospital in Hampshire, and is also a GP in general practice.
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Last revised: 4 December 2012
Next review: 4 December 2014