For Many Allergy Sufferers, The Dust Mite Is a Devil Indeed - Brief Article

National Wildlife, August, 1998 by Tom Dworetzky

Tonight, as you prepare to lay your head on your freshly fluffed feather pillow, consider one fact: It contains tens of thousands of tiny spiderlike creatures. "There are approximately a thousand dust mites in a gram of dust," says Thomas Platts-Mills, an allergy and mite expert at the University of Virginia Medical School.

Before you hurl your pillow across the room, however, consider the fact that these tiny creatures have been around for a long time--300 million or so years--and that they surely will always be with us. Mites were first identified in the outdoors. They were observed by Antonie Van Leeuwenhoek, who invented the microscope in 1674. But dust mites were so tiny that they were not discovered living in houses until the 1960s.

While they may be unstoppable, the good news is that dust mites don't hurt people: They don't bite (they are not bed bugs) or eat living flesh. In fact, their diet consists of the 50 million or so flakes of dead skin that pour off of our bodies each and every day. And the mites are completely benign and blind; they rely on random walking to move from one meal to the next.

The mite's real threat is to the estimated 15 million people in North America who are allergic to "house dust." What we think of as a common house-dust allergy is, in fact, most often an allergy to dust mites, or more specifically, to the pellets of fecal matter that mites pump out. "The mites' feces is perhaps 80 to 90 percent of the allergic component of house dust," notes Platts-Mills.

Hardy eight-legged creatures, dust mites are covered with chitin plates that afford them ample protection as they move around blindly. The creatures also have hairlike appendages that help them sense the outside world. They live for only about two months, so they must mature fast. In fact, about 10 days after birth, they hit mite "puberty," and start mating. "This they do enthusiastically," says Platts-Mills, noting that the male mounts the female for extended lengths of time. Not surprising: The tube delivering the sperm to the female is so small that only one sperm can travel down it at a time.

Once the female is impregnated, she delivers an egg of sizable proportions. "The female lays one enormous egg a day, an effort that would be equal to a human woman giving birth to a 50-pound baby," says the Virginia researcher. The female mite is about 300 microns in length, it turns out, and her egg is about 100 microns long.

Mites eat not just dead human skin, but specifically the white tendrils of mold growing on it. In the outdoors, they find mold to graze on wherever something is rotting--under leaves or in compost heaps, for example.

As these creatures move about, they simply stumble upon the flakes of our skin that rain down upon them, and defecate about 20 tiny pellets each per day. These pellets, which become temporarily airborne, are about the size of a grain of pollen.

When an allergy sufferer inhales the floating matter, an overreaction of the immune system causes the person's mucous membranes to release a number of substances, most notably histamine. Histamine causes inflammation and the symptoms we all think of as an allergic reaction: a runny nose, coughing, sneezing, swollen eyes, shortness of breath, wheezing and a scratchy throat.

That's why mite-controlling bedding and other anti-mite household gear is a growth industry these days. But despite the best efforts of entrepreneurs, the minute critters are pretty hard to eliminate. Even the tightest weave of most types of cloth has proved a giant opening for mites, which are so small that three of them could fit into the period at the end of this sentence.

Recently, however, a bit of apparently obsolete technology--the typewriter ribbon--has turned out to be a step forward in mite-fighting bedding. The weave of this material is sufficiently tight enough to keep much of the mite fecal matter from getting through, enabling a person to sleep peacefully atop sheets made of the material. And it is softer and more comfortable than the plastic liners often used by allergy sufferers to seal mattresses and pillows.

But beware of the more extravagant claims of those hawking mite-killing products: The experts warn that you might be getting misled. According to Platts-Mills, some remedies just are not worth the price. Since dust mites don't fly and tend to stick to surfaces, for example, air cleaners touted as mighty anti-mite busters may just be another case of blowing hot air.

"It's not possible with an air filter to control exposure to dust mites," he says. The reason: Most of the mites are found in the pillow or bedding on which you are lying, and the air you're breathing cannot be effectively filtered by a device in another part of the room.

If allergy tests confirm that the mite is the source of your suffering, experts recommend using mattress covers and pillowcases that seal closed. They also suggest removing any material, books or boxes from your bedroom that catch dust. If that room is as clean and dust-free as possible, you will have a better chance of mite-free sleep.