Do You Need an Air Filter?

If you are plagued by allergies and you've done all you can to reduce the allergens in your home, an air filter just might help you.

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"Buying an air cleaner is not my first suggestion," says Nathan Rabinovitch, MD, assistant professor of pediatrics at National Jewish Medical Research Center in Denver. "It's more of a backup recommendation."

Minimize Exposure First

Instead, minimizing your exposure to other allergens in the home is the first line of attack in reducing allergic and asthmatic reactions, says Rabinovitch, who offers these suggestions:

  • Avoid carpeting and use smooth flooring instead.
  • If you have pets, consider finding them a new home. If that's not an option, keep the pets outside. If that's not an option either, at the very least, keep them out of the bedroom, and certainly off the bed, and off as much of the other furniture in the house as possible.
  • Use air conditioning in the warmer months to get rid of outdoor pollens or allergens.
  • Clean all air filters, air conditioner filters, and duct filters at each change of season.
  • Keep your windows closed (at home and in the car) and avoid spending time outdoors when your allergies are acting up.
  • Ban indoor smoking.
  • Use the hottest water possible to rid your laundry of dust mites.
  • Avoid furnishings that gather dust.

Seek an Air Filter Second

If you have tried these tactics and aren't finding adequate relief, then it may be time to consider adding an air filter. Both the U.S. Environmental Protection Agency (EPA) and the American Lung Association recommend air filtration for people with allergies and asthma, but not as a solution by itself. Controlling allergy-causing pollution and ventilation are more important; there is disagreement on whether filters give much added relief from asthma in a clean and well-ventilated home.

This opinion is echoed by the Institute of Medicine, which has said "air cleaners are probably helpful in some situations in reducing allergy or asthma symptoms," but that air cleaning "is not consistently and highly effective in reducing symptoms."

But an air filter still might help you. There are five basic types:

Mechanical filters force air through a special screen that traps particles including allergens like pollen, pet dander, and dust mites. They also capture irritant particles such as tobacco smoke.

The best-known mechanical filter is the high-efficiency particulate air (HEPA) filter. HEPA (which is a type of filter, not a brand name) was developed during World War II to prevent radioactive particles from escaping from laboratories.

To qualify as a true HEPA filter, a device must be able to capture at least 90% of all particles 0.3 microns or larger in diameter that enter it. There are filters on the market that claim to be HEPAs, but may not be as efficient, so look for a system that meets true HEPA filtration standards.

Electronic filters use electrical charges to attract and deposit allergens and irritants. If the device contains collecting plates, the particles are captured within the system; otherwise, they stick to room surfaces and have to be cleared away. The most efficient filters are electrostatic precipitators, and the best of those use a fan.

Hybrid filters contain elements of both mechanical and electrostatic filters.

Gas phase filters remove odors and non-particulate pollution such as cooking gas, gasses emitted from paint or building materials, and perfume. They do not remove allergens.

Ozone generators are devices that intentionally produce ozone, which manufacturers claim cleans the air. They are not recommended by the EPA or the American Lung Association because ozone can be harmful to lungs at high concentrations. And the EPA says ozone at safe levels "have little potential to remove indoor air contaminants."

Still, if you do choose to use such a device, the American Lung Association advises "choosing one that ensures high efficiency over an extended period of time (at least several months) and does not produce ozone levels above 0.05 parts per million, either intentionally or as a by-product of its design."

If your home is heated or air conditioned through ducts, it may be possible to build filters into your air handling system. A whole-house system will also save space and additional noise in your home. On the other hand, the filters may be more expensive and more difficult to handle, and they may need to be changed more often.

Choosing a Device

The Allergy and Asthma Foundation of America suggests asking these questions before purchasing an air filter:

  • What is the efficiency rating of the cleaner in relation to the true HEPA standard?
  • Will the unit clean the air in a room the size of my bedroom every four to six minutes?
  • What is the device's clean air delivery rate (CADR)? The Association of Home Appliance Manufacturers rates air cleaners according to their clean air delivery rates (CADR), which indicate how much filtered air the cleaner delivers. There are different CADRs for tobacco smoke, pollen, and dust. The higher the numbers, the faster the unit filters air.
  • How difficult is it to change the filter? (Ask for a demonstration.) How often does it have to be changed? How much do filters cost? Are they readily available throughout the year?
  • How much noise does the unit make? Is it quiet enough to run while I sleep? (Turn it on and try it, even though you will probably be in a store and may not get a true sense of just how noisy it is.)

Those with lung conditions such as emphysema or COPD might also consider buying an air filter, says Paul Enright, MD, research professor of medicine at the University of Arizona. But if you're a healthy individual living in a relatively unpolluted environment, there's no need to spend the money.

Just remember, Enright says, that an air cleaning system is just one of the environmental changes you can make to alleviate symptoms. "There is no single appropriate answer to coping with allergies and asthma."

WebMD Feature Reviewed by Matthew Hoffman, MD on March 20, 2008


SOURCES: CDC. Natural Resources Defense Council. Gary Woodard, JD, MPP, assistant director for knowledge transfer, University of Arizona. Charlie Hollis, president, Mirex Aquapure Solutions, Houston. "Water-filtering systems," ConsumerReports. News release, "Purefecta Drinking Water Purifier From Pall and Kinetico Protects 'At Risk' Populations From Disease-Causing Organisms." "Drinking Water Treatment Systems and Products," Fact Sheet, Robert Falls &amp; Co. Public Relations.

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