For asthma and allergy sufferers who hate dust mites, a new scientific analysis from Denmark claims there may be little you can do.
The researchers in Denmark analyzed 54 previous dust mite studies that included a total of 3,000 asthma sufferers. They found that none of the available anti-dust mite products, such as special mattress covers or chemicals, significantly improved the patients' symptoms.
The researchers report that even if the products kill off some dust mites, the allergens they leave behind still cause difficulties. And despite a thorough scrubbing of sheets, there still is enough dust left around the home to make people sick.
But many allergy experts in the U.S. disagree and question the report's assertion that asthmatics should ditch their hypoallergenic products and cleaners altogether.
Currently, 22 million Americans suffer from asthma, and more than 6 million of them are children. For someone suffering from shortness of breath, dust mites that trigger allergic reactions only make breathing problems worse.
In fact, doctors estimate that 70 percent of asthmatic patients are sensitive to dust mites.
"Asthma is a highly complex disease," said Dr. Miles Weinberger, director of the Asthma and Allergy Center and the University of Iowa Children's Hospital, who noted a "high degree of variability in the studies" analyzed by the Denmark researchers.
Many outside factors can change the effectiveness of an anti-dust mite product — such as the local climate, humidity, other products in the room and even the sensitivity of the particular person with asthma.
"Dust mites like high humidity, which results in greater exposure and probably greater clinical importance in the U.S. Southeast and the UK than in northern climates, where central heating causes homes to be bone-dry in the winter," said Weinberger.
Apart from location, other allergies confound the difficulty to see if dust mites are the problem, or if products to fight dust mites are working.
"For example, if you are allergic to and exposed to cats or cockroaches or penicillin mold, it is likely to make little difference if you just reduce your exposure to dust mites," said Dr. David M. Center, Chief of the Pulmonary, Allergy and Critical Care Medicine at Boston University Medical Campus in Boston, Mass.
When doctors do recommend these products to patients, it's often part of a larger regimen of allergy controls and a house-wide approach to reducing asthma symptoms.
Anti-dust mite products may not work for all asthma sufferers sensitive to dust mites, but they may work for some. Before heading out to the store to stock up, asthma patients should ask their doctor to test for an allergy to dust mites, and make certain that they are exposed to significant amount of dust mites said Dr. Harold S. Nelson, professor of medicine at the National Jewish Medical and Research Center in Denver, Colo.
Even with that degree of selectivity, doctors hesitate to make any guarantees about household products.
"Essentially, I don't know if allergen-proof encasings help or not. They probably don't by themselves," said Center. "I do recommend them in combination with other environmental control measures for allergic asthma patients that need control measures beyond medicines, but I stress to patients that we don't really have proof for such measures — encasings, HEPA filters, etc."
Still, many doctors believe in taking simple, house-wide measures to fight dust mites such as washing sheets, replacing carpet with wood floors, keeping pets out of the bedroom or even putting the pillow in the freezer for five minutes.