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Jul 11

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What are House Dust Mites and How They Complicate Allergies ?

Lurking unnoticed, too small to be seen without the aid of a microscope, the house-dust mite is the natural scavenger within our homes.

Why are house dust mites a problem?

House-dust mites are members of the arachnid family — a family that includes spiders, chiggers, and ticks. Like spiders, they have eight legs, but the mites themselves are sightless and completely harmless, since they do not bite, sting, or transmit diseases of any description. Their natural diet consists of shed human skin scales, plant fibers, house dust, fungal spores, pollen grains, and insect scales.

In themselves, house dust mites pose absolutely no problems to people, unless, that is, you are one of the many thousands who have an allergic reaction to the proteins contained in their fecal droppings.

Huge populations of these mites exist in our homes, particularly within the fibers of bedding, carpeting, and upholstered furniture.To give you some idea of the size of creature you are dealing with, up to 1,000 individual mites can be counted in just 1 gram of dust (and there are approximately 28 grams in an ounce). This means that the average bed contains more than 10,000 dust mites and perhaps in excess of two million fecal pellets.

The usual route for these fecal pellets to enter the body is through contact with the mucous surfaces of the nose, the lining of the eyes, or the lining in the airways of the lungs. Being so tiny, once the pellets have been disturbed by such everyday actions as sitting on a bed or an upholstered chair, couch, or sofa, they remain airborne for at least 30 minutes before settling once more. These pellets also tend to settle at other sites within your home, such as in the fibers of curtains, drapes, or carpets. Children playing on the floor will therefore, be particularly at risk in carpeted homes.

House-dust mite biology

Just how many house-dust mites you have in your home depends not so much on how thoroughly you clean and dust, but rather on the indoor humidity and temperature.

House-dust mites do not drink to satisfy their thirst; instead they absorb water directly from the air through special glands in their skin. They grow best in a relative humidity of between 75 and 80 percent. Relative humidity is the percentage of the maximum possible amount of water vapor in the air – saturation, in other words -which, in turn, is dependent on the ambient temperature. Temperature is important because warmer air is capable of holding more moisture than is cooler air. If the relative humidity falls, there is simply not enough water vapor to allow the mites to thrive and reproduce.

One of the approaches in at least limiting the numbers of house-dust mite in your home is, therefore, to regulate the level of air humidity. This in itself cannot be a complete control, however, as mites have a protective mechanism to prevent excessive dehydration when the humidity falls.

Studies have shown that house-dust mites can maintain a water balance and survive at relative humidity of around 45 percent at 15°C/59°F; 55 percent at 25°C/77°F; and 65 percent at 30°C/86°F.

The other major factor apart from air humidity, regulating the number of house-dust mites that your home is likely to be playing host to, is the ambient temperature. Mites cannot shiver or sweat in order to regulate their own body temperature, and so they are entirely dependent on the temperature of the surrounding air for their survival. The ideal temperature, as far as the mite is concerned, is about 25°C/77°F. Therefore, if you keep the temperature of your home below this level you will inhibit their numbers.

The body temperature of house-dust mites governs their metabolic rate. This means that both egg production and life expectancy decrease at low temperatures, which leads to a decline in the total number of mites. This is the reason why people whose dust-mite sensitivity results in asthma attacks often find relief in high-altitude environments, where both humidity and the ambient air temperatures are too low for the mite to survive.

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