Information

House Dust Mites

Allergen Avoidance

Allergen Barrier Fabrics

House Dust Mites (and their allergens)
House dust mites are tiny creatures - no more than 1/3 of a millimetre in length when fully grown. They do most of us no harm at all and the majority of people live quite happily with them, unaware of their presence. Some people, because of their genetic make up, become sensitised to the allergenic proteins which dust mites produce and as a consequence they develop allergic conditions such as asthma, rhinitis or eczema. It is estimated that there are close to 500,000 people in New Zealand who are sensitive to house dust mites and around 100 million people world-wide. ...... If you are one of them you are certainly not alone.

Why are they a particular problem in New Zealand?
To survive, dust mites need humidity of more than 50% year round and temperatures which don't fall below freezing. The ideal conditions for their growth are 25°C and 75% relative humidity - making most of New Zealand and Auckland in particular a perfect environment for dust mites to flourish. The only regions of New Zealand likely to be dust mite-free are high altitude areas such the mountain ranges of the North and South Islands. This is not so much due to the freezing Winters - we rarely allow indoor temperatures to fall below freezing, but due to the lower humidity commonly found at high altitude.

House dust mites love to share our bedrooms with us!
Why? - well, every time we take off our clothes (or pyjamas) we shower them with the food they most enjoy - our skin! Coupled with this, the warmth and humidity that our bodies provide 6 or 8 hours every night creates the ideal environment for house dust mites to thrive.

Most of us shed over 1 gram of dead skin every day!
We are all continuously shedding tiny flakes of dead skin from our bodies and each time we undress, large amounts fall to the ground. A brand new dust mite-free carpet can become colonised in just a few weeks with dust mites eating their way through your discarded flakes of skin! Our dead skin continues to fall from us during the night as we lie in bed and the largest component of dust collected from mattresses and pillows is usually dead skin. The second largest component of mattress and pillow dust is the house dust mite population living on the dead skin along with their faecal droppings and the bodies of their dead ancestors! The bodies of the mites and in particular their faecal droppings contain the potent allergenic proteins which can trigger allergic disorders - asthma, rhinitis (inflamed, runny nose) and eczema. Reducing contact with these allergens can dramatically improve allergy symptoms.

Vacuuming removes only a few percent of dust mites.
Vacuuming alone is not an effective means of reducing the dust mite population, regardless of some salespersons' claims. The mites resist being 'sucked' into your vacuum cleaner by clinging to the carpet or upholstery fibres. Regular vacuuming of the mattress and bedroom flooring will reduce the allergen load to some extent but only the first minute or two is effective. Vacuuming for any longer has very little effect on the allergen levels.

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Allergen Avoidance                          Return to top of page

Research has shown that lowering exposure to dust mite allergens can help allergy sufferers by reducing the frequency and severity of their symptoms and by reducing their need for medication. To achieve these goals it is essential to understand the most important allergen reservoirs and learn how deal effectively with them. Many people waste a lot of time and energy cleaning their homes without having much impact on allergen exposure.

The Bedroom

1. The Mattress. In most homes, the mattress is THE major reservoir of dust mite allergen. The depth and complex construction of the mattress means that no amount of vacuuming or treatment with mite-killing sprays or powders (acaricides) will render it free from dust mite allergen. Complete encasement with a specialised allergen-barrier cover such as MiteGuard is the only effective means of protection. The allergen barrier cover should be lightly vacuumed or wiped with a damp cloth each week and hot water (at least 55°C) washed every 3 or 4 months to kill dust mites and prevent a build up of allergen on the cover.
   
   
2. Pillows. Pillows are a major source of dust mite allergen which our noses are pressed up against all night long! Most of the dust collected from pillows consists of flakes of dead skin and dust mite droppings! A MiteGuard pillow cover and regular weekly hot water washing of the outer pillow case will protect you from this major source of allergen.
   
   
3. Other Bedding. All sheets should be hot water washed weekly. Blankets should be hot water washed monthly (at least) or if woollen, dry cleaned. A duvet fitted with a MiteGuard cover and weekly hot water washing of the outer duvet cover is the best way of eliminating dust mite allergens from the outer bed covers.
   
   
4. Flooring. Polished flooring is really the best solution. Loose rugs which can be regularly cleaned will help create a more comfortable atmosphere if you prefer.
   
   
5. Soft Toys. Soft toys should be washable. If a regular schedule for washing the soft toys in hot water is adhered to from when the toys are new, allergen build up should be reduced to a minimum. Alternatively, regularly placing soft toys in the freezer overnight is an effective way of killing any dust mites which may have taken up residence. Older soft toys which have been "loved" for a long time may contain large amounts of allergen.
   
   
6. Dusting and Cleaning. Regular cleaning, putting things away, reducing clutter, removing hiding places for dust! All should be done as often as possible. When dusting furniture, window sills etc., use a damp duster to avoid "stirring up the dust". There is no need to vacuum more than once or twice a week but it is very important that your vacuum cleaner is properly maintained. Clean the filters and replace the dust bag frequently - don't wait until your vacuum cleaner stops sucking because the dust bag is overflowing! If dust created during vacuuming causes obvious problems to the allergy sufferer, buy a new vacuum cleaner with a very high efficiency 'HEPA' exhaust filter.
   
   
7. Curtains. When was the last time you had your curtains cleaned?! Curtains can become very dusty over the years. Have them cleaned once or twice a year and take the opportunity on a sunny day to air them on the washing line.
   
   
8. A note about hot water. Current building regulations require the fitting of 'tempering valves' to the hot water system. These effectively reduce the temperature of water in the washing machine to less than 55°C resulting in "hot" water washes that are not hot enough to kill dust mites. A plumber may be able to by-pass the valve, allowing hotter water to the laundry. Alternatively, consider buying a 'front-loader' washing machine which heats the water to 60°C.
   
   

Are dust mites a problem in the rest of the house?

The lounge is often found to contain high dust mite numbers, particularly in and around soft furnishings where people spend most time sitting - and shedding skin! Unfortunately it is very difficult to reduce dust mite allergens to low levels in most types of lounge furnishings. Frequent steam cleaning of fabric coverings can lower allergen levels but smooth coverings such as leather (if your budget will stretch to it) or vinyl are easiest to keep clean and will retain the lowest levels of allergen. As in the bedroom, smooth flooring with loose rugs which can be regularly cleaned are ideal. If you are lucky enough to have native timber floors hiding under your carpets, sanding and sealing will certainly be a very attractive option. Alternatively, regular steam cleaning of carpets and use of an air conditioner or dehumidifier can reduce dust mite populations and levels of allergen in the carpet. However, in older homes with timber joinery and floors, smaller domestic dehumidifiers are generally inadequate to reduce humidity to below 50% which is necessary to reduce dust mite survival. If your home does tend to be damp or musty, a dehumidifier can be of value by reducing the growth of moulds to which many allergy sufferers are sensitive.

If you have a family history of allergies, exposure of your new born child to high levels of dust mite allergen can increase the likelihood of their developing asthma in later life. Particular attention should be made to maintaining low allergen levels in the nursery, especially during the first year of life.

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Allergen Barrier Fabrics                      Return to top of page

Back in the early 1980s when the value of dust mite allergen protection was first recognised, allergen barrier mattress covers were made from vinyl - a very effective barrier but very uncomfortable to sleep on. The non-breathing vinyl covers caused perspiration which actually made symptoms worse for people with eczema. In the late 1980s some covers became available that were made from a vinyl-coated polyester cotton, which was marginally better but would still cause perspiration in summer.

In 1990 an article in the Lancet⁽¹⁾ medical journal described a new barrier fabric that was woven from polyester cotton and coated with a polyurethane compound which allowed moisture to diffuse through but which blocked dust mite allergen particles. This provided the allergy sufferer with protection and greater comfort, although this fabric too had its shortcomings. The membrane prevented air passing through, which still made the covers warm in summer and difficult to dry after washing. Also, the membrane had a limited lifespan and would break down after a few year's use.

Finally, in 1997 a study published in the Journal of Allergy and Clinical Immunology⁽²⁾ described a new type of barrier fabric that established new levels of comfort with effective allergen protection. This fabric was a precision microweave fabric with the trade name of "Pristine™". The study by Professor Tom Platts-Mills of the University of Virginia, demonstrated that Pristine™ fabric blocked dust mite allergen (Der p 1) particles to below detectable limits yet still allowed 86% of the air-flow that passes through a standard poly / cotton sheet. The key feature of this new fabric was the complete absence of any kind of coating or membrane that had prevented the air-flow through previous barrier fabrics. Instead, the allergen barrier property of this precision microweave fabric was achieved by the extremely tight and extremely accurate weave of the fabric. A number of different weaves with different gap sizes between the threads were initially tested and it was found that those fabrics with gap sizes of less than 10 microns between threads were effective in preventing Der p 1-carrying particles through the fabric. Precision microweave barrier fabrics now commonly in use have average thread gap sizes in the range of 6 to 8 microns providing the ideal combination of allergen protection and comfort. An additional advantage over the older coated fabrics is in the ease of laundering these newer fabrics as they can be hot water washed and hot tumble dried without any loss of effectiveness. In comparison, coated fabrics can take a long time to dry after washing and some would break down if exposed to high temperatures in tumble dryers.

Also included in Professor Tom Platts-Mills' study of allergen barrier fabrics was a "non-woven" polypropylene material made by the 3M™ Corporation under the name of Propore™. This fabric is made from the fusing together of a dense mesh of polypropylene fibres which is then bonded to a polypropylene based microporous film. This film has extremely small pores in it which allow the passage of a limited amount of air but which are small enough to prevent allergen particles passing through. Sometimes, bedding covers made from similar looking fabrics are offered for sale as allergen barrier covers. Usually these are found to be made from a non-woven polypropylene fabric but without a microporous membrane, giving a fabric with relatively large gaps between the fibres. (see images). Needless to say, while the price of these covers may seem attractive, they do not provide an effective barrier to dust mite allergen.