Advice to Clean Filters May Be Hot Air

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March 5, 2000 (San Diego) -- Scrupulous cleaning of air ducts, often touted as an important way to reduce allergy-causing substances, or allergens, in the home, may not be as helpful as many people think, according to a study presented at the annual meeting of the American Academy of Allergy, Asthma and Immunology here.

Because little, if any, research existed on the levels of allergens in home air ducts, researchers at the Charlottesville, Va., environmental company Indoor Biotechnologies measured the levels of dog, cat, and dust mite allergens in dust samples collected from beds, sofas, carpets, and air ducts in 20 homes in northern and central Virginia. To measure allergens in the air ducts, they compared dust taken from the "return" duct, which returns room air to the heat pump system, to samples collected from the "in" duct, which carries the filtered air back into the room.

The investigators found high levels of dog, cat, and dust mite allergens in the carpets and furniture of the vast majority of houses. However, dog and cat allergen levels were 85% lower in the "in" ducts compared to the "return" ducts, indicating that "although there is significant accumulation of cat and dog allergens in return air ducts, the filters present in the duct systems dramatically reduce allergen levels passing back into rooms via 'in' ducts," says Amy Tsay, biotechnology research and development specialist at Indoor Biotechnologies. They also found minimal accumulation of dust mite allergens in the air ducts. "This suggests that there were no mite allergens going in because the air ducts are not a good environment for mite growth," Tsay tells WebMD. "People who promote air duct cleaning to reduce mites -- there are no mites in there."


Taken together, the results suggest that the air ducts present in standard home heating systems already do a good job of filtering out dog and cat allergens, says Tsay. "The surprising thing is that there is accumulation of pet allergens in the duct, but it's just not blowing back into the room air." She concludes, "There is no benefit to be gained by changing the filters. ... [P]eople should put more emphasis on cleaning mattresses and mattress casings and other things, and not spend so much time cleaning the air ducts." Data from other studies presented at the conference revealed that even one's choice of pillows can make a difference: Researchers at Wythenshawe Hospital in Manchester, England, found that pillows made of synthetic materials harbor significantly more dog, cat, and mite allergens than feather pillows.

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