You may have bought an expensive mattress protector to keep off allergy-inducing dust mites. Your doctor may have even recommended that you use one if you have suffer from allergy problems but your efforts and your money are apparently in vain, as researchers of a new study has concluded that dust mite covers may not actually alleviate your allergy problems.

In a study "Impermeable dust mite covers in the primary and tertiary prevention of allergic disease: a meta-analysis" published in the March issue of the Annals of Allergy, Asthma and Immunology, researchers used data from 24 trials of methods that could reduce dust mite exposure and prevent allergy.

The researchers found that while using mattress covers can reduce exposure to dust mites by about 20 percent, the reduction is not significant enough to prevent dust mite sensitization and allergy signs and symptoms such as runny nose, wheezing, asthma and dermatitis.

"Based on this analysis which combines data from many different studies, there doesn't seem to be any benefit to using dust mite covers to prevent allergic disease or to prevent symptoms," said study author Whitney Arroyave, a researcher with the Tulane University School of Public Health and Tropical Medicine in New Orleans.

The researchers also said they found no evidence that could support claim that mattress covers can prevent allergy problems. "No evidence was found to support the use of impermeable mattress covers in the primary prevention of allergic disease or in the tertiary prevention of allergic disease symptoms," the researchers wrote.

Despite the study's findings, some doctors do not plan to stop recommending the use of dust mite covers. "This article is helpful to show a single measure to control allergies is not always effective - we have to use multiple measures," said Samuel Friedlander, an allergist at the Case Western Reserve University School of Medicine in Cleveland, Ohio. "So the take home message for me is that dust mite covers are still very important, but they should be part of a comprehensive treatment plan."

Friedlander said he does not want people to think that dust mite covers are useless. "I think the point is that we need to make multiple recommendations to relieve multiple allergies that our patients are allergic to," he said. "Dust mite covers are very important, but they have to be part of a comprehensive treatment plan."