The ads are enticing — buy an air filter and you’ll breathe easier, get sick less often and feel generally better. “Purify” what you breathe in and the wheezing, sniffling and coughing associated with pollen and dust will become a thing of the past, commercials for filters tout. While it seems logical that a filter can suck allergy causing particles from the air and quell symptoms, do these products really help?
So far, there’s little hard evidence that filters can prevent allergies and block asthma. Round up a group of experts and you’ll get a mix of responses, ranging from the opinion that filters can indeed help people breathe easier to the belief that they are next to useless.
Studies of air filters have provided equally mixed results, some showing a small reduction in symptoms and some showing no benefit at all. And even when researchers reported a reduction in symptoms, they did not find that asthmatic patients could get by with less medication or had improved scores on breathing tests, according to the authors of an article recently published in the journal Chest that reviewed studies on air filters.
Dr. Andre Nel believes that filters can help if the source of breathing problems is pollen. Unlike some other allergens, such as dust mites and cat dander, pollen is likely to be suspended in the air, says Nel, a professor of clinical immunology and allergy at the University of California at Los Angeles.
“But the filter should not be your primary method of prevention,” he adds. “Pollen comes from the outside, so the most important thing you can do is keep the windows and doors closed. That dramatically affects the pollen counts indoors.”
If the doors and windows are closed most of the time, then the filter can help clean up any pollen that slips through, Nel says.
Still, Dr. Marjorie Slankard points out, you may do perfectly well with no filter if you have an air conditioner. “An air conditioner with a good filter will take out over 90 percent of the pollen and mold,” says Slankard, an associate clinical professor of medicine at Columbia Presbyterian Medical Center in New York.
For patients who want that extra bit of air purification, Slankard does suggest purchasing a filter. And if you’re only going to buy one filter, she advises that it be placed in the bedroom.
Not for pet allergies
At the other end of the spectrum is Dr. Andrea Apter, an associate professor of medicine at the University of Pennsylvania in Philadelphia.
“I don’t encourage patients to go out and buy air filters,” Apter says. “There’s not a lot of data that really supports their use.”
Often patients with pet allergies ask if a filter can help. “You can’t have a cat and an air filter and live happily ever after,” Apter says.
The reason may be that much of the cat dander in your house is not in the air, according to Nel.
“The cat antigen is very sticky,” he explains. “And in a house where you have a cat, the antigen is on the walls and floor surfaces where it will dry and come off slowly. In houses where the cat has been removed, the antigen can be present for months afterwards.”
When it comes to dust mite allergies, filters may be equally ineffective, Nel says. That’s because this antigen is also often not airborne. Rather, it just accumulates in places like pillows, mattresses and rugs, he says.
The best prevention for allergies to dust mites is to put water impenetrable covers on mattresses and pillows, Nel says. “That prevents the dust mite antigen from getting out,” he adds.
Linda Carroll is a free-lance reporter based in New Jersey. Her work has appeared in The New York Times, Health and Smart Money.