When flowers start blooming, pollen is looming, causing misery for millions of people with allergies . Advertisements for indoor air cleaners claim that they remove allergens and can make our lives sneeze-free. But do they really work?

Don't toss your tissues just yet, say the experts. Studies haven't shown definitive improvement for allergic patients who use air cleaners. More research is necessary.

Research on Air Filters

Nathan Rabinovitch, MD, a pediatric asthma specialist at Denver's National Jewish Medical and Research Center, is currently analyzing the data from his study of the effectiveness of air cleaners for children with asthma.

Dr. Rabinovitch and his colleagues used a type of portable air cleaner known as an electronic precipitator along with a vacuum cleaner equipped with a HEPA (high-efficiency particulate air) filter. The combination of the two devices is important, he stresses, especially for homes with carpeting, because a portable air cleaner cannot remove allergens once they've hit the ground.

The Study's Results

"There was about a 60% drop in airborne particles in the household," says Dr. Rabinovitch. He isn't yet certain, however, whether this was due entirely to air-cleaning devices or to other factors. The children in the study were monitored individually both indoors and out. The devices they wore showed particle reduction more along the lines of 20% to 25%, probably a more realistic number because it reflects their exposure during ordinary activities.

Dr. Rabinovitch cautions that he has yet to determine whether this particle reduction improved his patients' health. A previous study found that a HEPA air cleaner did reduce levels of cat-allergen, but failed to produce any improvement in allergy symptoms.

Cleaning Is Still Important

"One of the dangers is that people will buy a product that they don't need," says Dr. Rabinovitch, "and the other is that they'll think they don't have to clean their houses."

If you're allergic, you must make every effort to control the source of the allergen, which may mean getting rid of a pet, removing carpeting, using allergen-impermeable encasings, frequent laundering of bedding, and controlling of cockroach populations. Air cleaners cannot substitute for a clean environment.

Types of Air Cleaners

There are different types of air cleaners. Two are listed below:

  • True HEPA filters—These filters are the most effective air filters; they are found in both portable cleaners and vacuum cleaners. Don't be fooled by the term "HEPA-like."
  • Electronic precipitators—These are also good models, but their efficiency decreases over time. (These are not the same as electrostatic ionizers; see below).

What to Consider When Buying

Consider the following factors when looking for an air cleaner:

  • Clean air delivery rate (CADR)—Look for a CADR that matches the size of the room you want cleaned. CADR measures the amount of clean air delivered per minute. For a room of 80 square feet, a CADR of 50 is about right; for 320 square feet, look for a CADR around 200. (The ratio of room size to CADR is approximately eight to five.)
  • Whole-house cleaner versus a portable model—If you have central heating and air, which constantly recirculates contaminated air throughout the house, you should opt for a whole-house cleaner.
  • Noise levels—Remember, air cleaners must run continuously to work properly, so you'll have to tolerate any noise they generate. Cleaners are most efficient at their highest fan speeds, which can be noisy. Be sure to test it before you buy it to see if the noise is too much for you.

Buyer Beware

If you scout for air-cleaner information on the web, you may encounter more hype than help. Beware of the following:

  • Ozone generators—Avoid these models completely. Although some manufacturers assert that ozone is a natural purifier (it does eliminate odors but not particles like pollen), they neglect to mention that breathing ozone can damage the lungs. Sometimes manufacturers call ozone "activated oxygen."
  • Negative ionizers (also called electrostatic ionizers)—These units charge incoming air with negative electricity, causing particles in the air to be attracted to objects like your walls and floor. This removes allergens from the air, but it also makes your house filthy. Air cleaner units that contain an ionizer and an internal filter plate to trap dirt are acceptable.
  • Antimicrobial protection—Because filters tend to collect moisture and can, therefore, become breeding grounds for bacteria and viruses, some manufacturers have their products treated with antimicrobial agents. Not only is there no proof that this improves health, but the toxic antimicrobial chemicals can themselves be released into the air. In addition, some scientists are concerned that overuse of antimicrobial agents will create resistant strains of bacteria.

Consumers should also be aware that while the American Lung Association recommends air cleaners, it has a funding partnership with air-cleaner manufacturer Honeywell.