Dust mites are close relatives of spiders, scorpions and ticks (arachnids). There are several species of dust mite, but the most common European species are Dermatophagoides pteronyssinus and the smaller Euroglyphus maynei. Over 85% of asthmatics are sensitive to the house dust mite, making it one of the primary triggers of asthma attacks. The main trigger are allergens in the faecal pellets which mites excrete and which build up in soft furnishings, such as bedding, sofas carpets or curtains. Vigorous activity, such as vacuuming, dusting, or even walking of soft furnishings can make the dust mites' faeces become airborne. Dust mites are smaller than the full stop at the end of this sentence.

We inevitably inhale these particles and people who are sensitive to dust mites can suffer an allergic reaction.

Dust Mites and Humans

House dust mites feed on human skin that sloughs off our bodies. Newly-shed skin scale is not suitable for the mite. It is too fatty and dry for the dust mite to ingest. However, the skin that we shed often becomes infested with a fungus called Aspergillus repens which takes out the fat and adds water, thereby making our shed skin perfect for the dust mite's nutritional needs. The mite excretes and re-ingests the faecal pellets containing skin cells to extract all the nutrients. This can happen over 6 times before all the nutrients are extracted. In the meantime, the level of faecal pellets containing dust mite allergens builds in the dust.

Dust Mites Share Our Beds

Dust mites have thin, permeable skin, which makes them vulnerable to water loss. Hence, dust mites like to live in places of high humidity. In general humid homes have more mites and therefore more allergens. Dust mites also need to be in a location that will provide a constant supply of human skin. The most common place to find house dust mites is in our beds! We shed approximately 1g of skin a week in our beds, and we spend up to eight hours a day there, producing about a pint of water in sweat, which causes the relative humidity to remain at a high level. House dust mites can also be found in carpets, sofas and clothing which is used by the mites as a means of transportation from room to room. If sites like mattresses and pillows that accumulate skin scales are not cleaned often and thoroughly the mite populations can build up over many years.

Dust Mites, Breathing Difficulties and Shortness of Breath

Dust mites live for about 3 months and produce around 2000 faecal pellets each, containing digestive enzymes. Many people are allergic to these enzymes. The precise mechanism of action is still under debate, but more people react to the dust mite than any other form of allergens. Over 85% of asthmatics react to them.

The bodies response to an allergen starts with localized inflammation, as the immune response is triggered. Sensitive people react within minutes and if uncontrolled, the airways can spasm, making breathing difficult.

If exposure to the dust mites continues over a long time the muscles in our airways change shape and become less flexible, usually referred to as remodeling. When this happens, an allergic response causes spasm, but takes longer for the muscles to relax allowing normal breathing - the wheezing and shortness of breath associated with an asthma attack.

In short, the house dust mite allergen plays a major part in the development of allergic asthma.

Dust Mite Prevention

If you suffer from mite-induced asthma, reducing the number of mites and level of mite faeces, and therefore allergen in the house can make an immeasurable improvement to your quality of life. By reducing the allergen levels in the home (either directly or by removing the dust mites) the trigger that starts inflammation, which leads to the asthma attack are also removed. In reality effective removal takes time, but the likelihood of an asthma attack being provoked decreases. However, there may be no noticeable improvement in health for several months, so do not assume that the changes are ineffective because the asthma does not disappear overnight. Several simple measures can do this:

Dust Mites and Bedding

Most of the dust mites in your house live in your mattress. Its an ideal environment for both warmth and moisture from your body heat and perspiration. Effective treatment has 2 stages - removal of the allergen reservoir, then killing of the dust mites to prevent the allergens from building up again.

Vacuuming with a heap vacuum filter is an effective way to reduce the allergen level, especially for the mattress. Some companies offer a commercial service, which heat the mattress to kill the mites and also destroy the allergens.

Dust Mites cannot stand hot water and the allergens are very water soluble. Washing your bedding in very hot water (65 C) every week kills the mites and also removes the allergen reservoir.

Washing pillows is also advisable, but this would require synthetic pillows. Some people have reported better control with down pillows, but this may have been because the cotton covers for down is thicker and a tighter weave than for synthetic or foam.

If hot washing is not possible, 24 hours in the freezer will kill all the dust mites in a pillow. This will not remove the allergens, so should be followed by a cold wash.

Having reduced the allergen and mite levels, the most important step you can take is to encasing the mattress, pillows and duvets in anti-allergenic bedding. These are made with a fabric with very small pore sizes, which prevent any remaining allergens escaping and getting into your airways. Look for products made from materials which are flexible and allow free exchange of moisture - otherwise it can feel like sleeping on a plastic sheet.

Allergen avoidance is a continuous process. Dust mites will grow back and a good treatment regime should be repeated every 6 months. In the meantime, Turn back the bed clothes during the day, leave the windows open if possible and dispose of, and replace, mattresses and pillows over 10 years old (after 10 years 70% of the solid weight of the pillow is likely to be dust mite excrement).

Dust Mites and Carpets

Dust mites love carpets, the longer and thicker the better, so a hardwood, tile or linoleum floor instead of carpet will help. If you must use carpet, try not to place it on concrete because the warm space between the carpet and concrete is a good place for the dust mites to live.

Vacuuming your carpets and upholstery every week can help. Vacuums with high-efficiency (heap) filters pick up more dust mites. It is important that vacuuming be carried out with a good quality cleaner that does not pump the dust straight back out. This, as well as having little effect on the allergen levels in the home, can also provoke an asthmatic attack.

Plastic or wood furniture that doesn't have much padding can also help keep down the number of dust mites in your home. Because dust mites love warm, humid places, keeping the humidity low by using a dehumidifier or running air conditioning can make a difference. Special air filters can help reduce dust mites in the air.

Dust Mites, Ventilation and Humidity

Dust mites need high levels of relative humidity to flourish. So increase ventilation and reduce the humidity around the bed and in the home generally. This makes the home less habitable for house dust mites. Increasing ventilation prevents a build-up of dust, etc. in the home, which may irritate the throat and provoke asthmatic attacks. An alternative is to invest in a ventilation unit with a heat exchanger. This will increase the air changes in a room without affecting the temperature, extract allergens from the room and prevent allergens from entering.


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Page updated 17th Jan 2008, 11:26

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