The Ache: In cold and flu season, pathogens spread when people are crammed into close quarters, such as airplanes and cars.

The Claim: Personal air purifiers worn around the neck clean the air in the wearer’s breathing zone of viruses and bacteria as well as allergens, say companies that sell them.

The Verdict: The devices helped clear a variety of test particles from the air in lab tests, but scientists say there’s no proof they have any health benefit in real conditions.

“It sounds like it worked in a laboratory setting, but that doesn’t say anything about whether it works in real life,” says Darryl C. Zeldin, scientific director of the National Institute of Environmental Health Sciences, an arm of the National Institutes of Health. Theoretically it is possible that the devices might help reduce transmission of pathogens, or ease asthma symptoms, but proof is needed, he adds.

Personal air purifiers work by emitting electrically charged molecules or atoms called ions, companies say. The ions transfer the charge to particles—such as one carrying a flu virus—in the user’s breathing zone and since like-charged particles repel each other, they are pushed out of the breathing zone, companies say.

The AirSupply Minimate from Wein Products Inc. in Los Angeles, emits positive ions and fits in the palm of the hand. The AirTamer A310, new last year from

Headwaters Inc.

in Marblehead, Mass., emits negative ions. It recharges through a USB port and holds the charge for 150 hours of continuous use, says company co-founder Troy Anderson. Both devices have suggested prices of $150.

In lab tests funded by Headwaters, the AirTamer was found to efficiently clear cigarette smoke, Mr. Anderson says.

In research partly funded by the company, Wein’s technology has undergone a battery of testing by University of Cincinnati scientists. In a study, published in the journal Indoor Air in 2005, a prototype of the Minimate was tested for removal of particles, including salt particles in a variety of sizes and a bacterium that doesn’t usually cause disease. It cleared the air of half of the test particles after 15 minutes, and nearly all of them within 90 minutes, according to the results.

The particles remain present on surfaces, “but at least you reduce inhalation exposure,” says study author Sergey A. Grinshpun, a professor of environmental health at the university. Since the particles used in the test were similar to the size of bacteria and particles carrying infectious viruses, it wasn’t necessary to use infectious particles in the test, he adds.

Dr. Grinshpun’s study appears nicely done, but doesn’t reflect real-life conditions, says Werner E. Bischoff, an infectious-disease specialist at Wake Forest Baptist Medical Center in Winston-Salem, N.C. In the lab tests, the particles are introduced only once and the purifier is given time to clear them, he adds, but “if you sit next to a person in an airplane, this person will sneeze and cough during the entire eight-hour flight.”

AirSupply Minimate emits positive ions and fits in the palm of the hand.


Photo:

F. Martin Ramin/The Wall Street Journal, Styling by Anne Cardenas

Colds and flus are transmitted not just by air, but also by people touching surfaces, Dr. Bischoff adds. It’s always a good idea to avoid touching your nose or mouth after touching the back of an airline seat.

The Cincinnati researchers also found the Minimate prototype reduced the concentration of “viable” airborne bacteria, defined as bacteria that grow well on a petri dish, Dr. Grinshpun says. It isn’t known exactly what causes the inactivation of bacteria, he says.

Headwaters’s Mr. Anderson and

Stanley Weinberg,

CEO and chairman of Wein, both say that while it’s difficult to test the devices for real-world benefits, customer feedback has been positive.

Scientists caution that the antibacterial effect could be caused by a gaseous byproduct of the device, such as ozone, an air pollutant. Both Messrs. Anderson and Weinberg say their devices produce negligible amounts of ozone. Mr. Weinberg adds that the Minimate has also tested negative for hydrogen-peroxide emission.

In 2006, a personal air purifier exploded on a Continental Airlines flight, according to a National Transportation Safety Board report. According to the report, the problem was probably caused by the user recharging a non-rechargeable battery; there were no serious injuries. The device, called the Fresh Air Buddy and formerly manufactured by Wein for another company, is no longer made, says Mr. Weinberg.

Whether you’re allowed to take an air purifier on an airplane depends on the carrier. United Airlines, which now owns

Continental,

doesn’t allow the air purifiers in the cabin based on the results of an “internal review,” a spokeswoman says. There is no Federal Aviation Administration restriction on carrying personal air purifiers on board, but each airline can make its own call, an FAA spokeswoman says.

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