The Associated Press

Two studies found that mite-proof bed coverings, at least by themselves, fail to relieve asthma and allergies, a perplexing discovery that challenges the frequent advice of doctors.

Doctors and medical groups widely recommend mite-proof bed coverings to treat allergies and the asthma they can cause.

Up to 50 million Americans have allergies. Studies suggest that 40 to 60 percent of allergy sufferers in some areas are sensitive to dust mites, near-microscopic creatures that live in house dust and lay eggs in bedding. The tightly woven coverings typically priced around $120 for a set hold in their irritating allergens and keep new mites from bedding.

"My son had bad allergies, so we bought them and I don't think we would now," said Dr. Jeffrey Drazen, a respiratory specialist who is editor-in-chief of the New England Journal of Medicine. "They deserve to work. It made sense."

The findings of the two European studies, reported Thursday in the journal, were so surprising that some doctors vowed to keep recommending bed coverings.

"For my patients, I wouldn't dream of not doing it," said Dr. Thomas Platts-Mills, a University of Virginia allergist who wrote an accompanying commentary on the studies. "It's on the side of the angels: you're not taking drugs."

Though small previous studies reached mixed conclusions on the value of bed coverings, there is strong evidence that blocking allergens relieves symptoms. For example, asthmatics improve at clinics or hospitals with fewer mites.

Yet, in a seeming paradox, the yearlong European studies found no difference in symptoms between people with and without bed coverings. The English study was the largest of its kind, with 1,122 asthma patients. The Dutch study looked at 232 patients with hayfever-like allergies.

The researchers and specialists familiar with their findings said there may be so many dust mites around homes that they can largely eclipse the effects of mites in bedding. Pet, mold and other allergens may also confuse the question.

Some research also suggests that asthma may perpetuate itself after prolonged exposure, even once the irritants are removed, said Dr. Adnan Custovic, supervisor of the English study and allergist at Wythenshawe Hospital, in Manchester, England.

The Dutch study's lead researcher, allergist Dr. Roy Gerth van Wijk at Erasmus Hospital, in Rotterdam, said he was previously prescribing bed coverings to nearly all his patients with asthma or hayfever-like symptoms. Now, he says he recommends them to about 5 percent and only "when it is part of a radical change of the house."

In addition to taking medication, some allergy sufferers wash bedding regularly, vacuum with strong filters, replace carpet and curtains with hard floors and blinds, steam-clean furniture and cover upholstery. Other measures include dehumidifiers and mold-killing cleaners in kitchens and bathrooms.

"You really have to address the entire housing design," said Custovic. "Even if you do it, will it be effective? We don't know."

Others insisted that bed covers should help, especially if such steps are taken to remove allergens elsewhere around the home. "Does this mean you shouldn't put impermeable bed covers on your beds? No, it doesn't mean that at all," said Dr. Darryl Zeldin, who researches mite allergies at the U.S. National Institutes of Health.

"We really know they work. The users say that to us," added Kea van Dygk, sales office manager at Hal Allergy in the Netherlands, whose coverings were used in the Dutch study.

On the Net

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