Dust mites are microscopic spider-like creatures that feed on flakes of human skin and reside in bedding, carpets, upholstery, draperies and other "dust traps." Dust mite allergens substances which can cause an allergic reaction are proteins found in the mite's feces.
The purpose of the study was to evaluate practical methods for lowering these allergens in bedrooms of low income, urban homes. Thirty-nine homes in Seattle, Washington, were studied. Pillows, box springs, and mattresses were encased with allergen-impermeable covers. Bedding was washed weekly in hot water either in the home or professionally. Carpets received a single treatment of intensive vacuuming plus dry steam cleaning or intensive vacuuming alone. Upholstered furniture received either dry steam cleaning or intensive vacuuming.
The results were published today in the online version of the journal of the National Institute of Environmental Health Sciences, Environmental Health Perspectives, and will appear in the August issue of the journal. The senior author of the report is Darryl C. Zeldin, M.D., of NIEHS, one of the institutes of the National Institutes of Health.
Recent studies have shown that exposure to house dust mite allergens is a significant risk factor for the development of allergic diseases, such as asthma and rhinitis (hay fever). NIEHS' Dr. Zeldin said, "Results from an earlier study suggest that over 45 percent of U.S. homes, or approximately 44 million dwellings, have bedding with dust mite allergen concentrations that exceed a level that has been associated with allergic sensitization. We estimated that 22 million homes have bedding with dust mite allergen concentrations at a level that can trigger asthma in susceptible people. So we were eager to test ways to reduce these troublesome substances."
The researchers found that the interventions significantly reduced house dust mite allergen concentrations. The use of allergen-proof covers and either professional or in-home laundering of bedding reduced allergen levels in beds. Both dry steam cleaning plus vacuuming and vacuuming alone lowered allergen levels in carpets. Vacuuming and dry steam cleaning each reduced allergen levels in upholstered furniture. Dry steam cleaning machines have recently become available for home use.
"The decreases in dust mite allergens following a single vacuuming did not last as long as decreases following dry steam cleaning and vacuuming. We believe that the hot dry steam kills the mites, and the vacuuming removes them from the carpet," Dr. Zeldin said.
While the vacuuming and steam cleaning procedures reduced allergen concentrations below the levels believed to trigger asthma symptoms, the interventions did not reduce the concentrations below the levels associated with allergic sensitization. Sensitization the process by which the body's recognition of a particular allergen leads to a physical response is the first step in allergy development.
"In order to obtain allergen measurements below the sensitization level, people may need to do additional things such as remove carpeting from the floors, replace upholstered furniture with leather or vinyl covered furniture, and reduce humidity levels in the house," Dr. Zeldin said. "However, such a bare-bones home may be less desirable to the residents. In the meantime, more research is needed on inexpensive alternatives for maintaining long-term allergen control."
Other researchers on the allergen study include Sandra Randels and James Stout, Ph.D., Department of Pediatrics, University of Washington, Seattle, Michael Muilenberg and Harriet Burge, Ph.D., Department of Environmental Health, Harvard School of Public Health, and Henry Lynn, Ph.D. and Herman Mitchell, Ph.D., Rho, Incorporated, Chapel Hill, N.C.