Patients were randomly divided into either an intervention group receiving nonpolyurethane dust mite covers, or a placebo group receiving covers dust mites can permeate. During the study period, daily peak flow and asthma symptom scores were recorded, and dust samples from the mattresses were taken.
87 Percent Reduction in Dust Mites
The study found that use of dust mite-impermeable covers resulted in an 87 percent reduction of dust mite allergens. Upon follow-up, researchers noted that the morning peak flow measurements of the patients in the intervention group improved significantly.
The study concluded that dust mite avoidance measures, such as the use of bed covers, may have beneficial effects on not only allergen reduction, but also in approving asthma symptoms. Past studies have shown that using bed covers reduces allergens, but this study is the first to show a link between allergen reduction and improved morning peak flow readings.

