Peter C. Gotzsche, MD, DrMedSci, director of the Nordic Cochrane Center in Copenhagen, Denmark, and colleague H.K. Johansen, MD, DrMedSci, analyzed 54 clinical trials involving more than 3,000 asthma patients.
In each trial, researchers took on house dust mites with physical methods such as mite-proof mattress casings and vacuums, mite-killing chemicals, or a combination of physical and chemical methods to fight the mite.
"We were unable to demonstrate any clinical benefit to mite-sensitive patients with asthma," Gotzsche and Johansen write. "We conclude that the trials of current chemical and physical methods aimed at reducing exposure to house dust mite allergens failed to find an effect."
The finding may come as a surprise to people allergic to dust mites, many of whom have spent -- and are spending -- serious time, money, and effort in their battle against the bugs.
Dust Mites Small in Size, Great in Number
House dust mites fall into the category of things we'd rather not think about. They are as ugly as they are small. And they are very small. Ranging in size from a hundredth to a thousandth of an inch, they're too small to see without magnification.
Like spiders, dust mites are eight-legged arachnids. The good news is they don't bite. The bad news is they do eat the dried, dead skin that sloughs from our bodies every day. It's a rich source of food, as we shed about a fifth of an ounce of skin a day. It makes up about 80% of the dust you see in an indoor sunbeam.
As many as 19,000 dust mites can be found in a ball of dust the weight of a 1 gram paper clip, although the typical dust ball contains only 100 to 500 mites. Contrary to popular belief, dust mites don't live in your heating/air ducts. But they love living in your mattress and in your pillow, where your body provides them not only food but also the moisture and warmth they crave.
Hideous to behold under the microscope, dust mites themselves aren't really a problem. But their shells, their feces, and their corpses break down into potent allergy-causing proteins or allergens. That's why just killing dust mites isn't enough. Dust-mite control means getting rid of dust-mite dust, and -- because you can't totally get rid of them -- keeping dust-mite populations low.