Indoor Air Quality News

Report Finds Even Most Effective Air Cleaner Could Be Questionable Investment

Even the best air cleaner can be a frivolous investment. There's little evidence that they alone will reduce the effect of indoor pollutants for those with asthma or allergies, Consumer Reports (CR) announced on Sept. 6.

In its October report, "Air Cleaners: Some Do Little Cleaning," Consumer Reports ( presents the results of independent tests for room and whole-house air cleaners.

The report also advises consumers to try other simple indoor air-cleaning steps before considering an air cleaner.

Relatively few air cleaners excelled in the CR tests, especially among room models, which account for the most sales, as measured in dollars. Many room air cleaners scored fair or poor in at least one of CR's four cleaning tests for dust and smoke.

In May, CR published "New concerns about ionizing air cleaners," which concluded that some ionizing models did a poor job of cleaning the air and several can expose users to potentially harmful levels of ozone, an irritant that can worsen asthma and decrease lung function. CR's October report features ratings of 30 room air cleaner models as well as 24 whole-house models, based on testing conducted for previous reports as well as for the current report.

"Our test findings should be a major concern for consumers who are bombarded with advertising for these air cleaners," said Dr. Jeff Asher, vice president and technical director for Consumers Union, the publisher of Consumer Reports. "Consumers need to know that they may be spending money on models that don't clean the air and have no proven health benefits. Some may actually cause harm," he said.

Some room air cleaners that have electrostatic precipitators, which trap charged particles on oppositely charged plates or filters, are effective at cleaning the air. But other models that use this same basic technology are far less effective.

CR suggests avoiding electrostatic room air cleaners with a small fan or no fan, which have cleaned poorly in our tests and can emit significant amounts of ozone. CR also advises consumers to avoid dedicated ozone generators, which were not tested for this report. Unlike electrostatic precipitators, which emit ozone as a by-product of their cleaning process, these niche products produce large amounts of ozone by design.

Professionally installed whole-house models performed best overall in CR's tests, but are pricey. Whole-house electrostatic precipitator models emitted little ozone and performed well. But the best cost $500 to $700 for the unit and another $200 or more to install and can only be used if your home has central hot-air heat or air-conditioning.

Bacteria in Household Dust May Trigger Asthma Symptoms

New research announced on Sept. 7 finds that bacteria lurking in household dust produce chemicals that may trigger asthma and asthma-related symptoms such as wheezing. These bacterial chemicals, called endotoxins, particularly those found on bedroom floors, were linked with increased respiratory problems in adults.

This study, supported by the National Institute of Environmental Health Sciences (NIEHS), a part of the National Institutes of Health, is the first nationwide study of endotoxins in the household environment, and it involved analysis of more than 2,500 dust samples from 831 homes across the United States.

Researchers at NIEHS and the University of Iowa found a strong association between endotoxin levels and the prevalence of diagnosed asthma, asthma symptoms, asthma medication use, and wheezing. These relationships were strongest for bedroom floor and bedding dust. Households with higher endotoxin concentrations experienced higher prevalence of respiratory symptoms.

Endotoxins are found in the cell wall of bacteria and are only released when bacteria ruptures or disintegrates. Because bacteria can be found everywhere in the home, the likelihood of their release is high. Once released, endotoxins can cause inflammation of the airways and lead to asthma symptoms.

The study was conducted using samples from The National Survey of Lead and Allergens in Housing (NSLAH).

Two research assistants visited each household, administered a detailed questionnaire, conducted a home inspection, and used a standardized protocol to collect samples. Dust samples were collected from bedroom, kitchen and living room floors, bedding, and upholstered furniture and assayed for endotoxin. A disease association analysis was performed to correlate endotoxin concentrations to specific health outcomes.

"When we analyzed the dust samples, we found that kitchen and living room floors had the highest concentrations of endotoxin," said Darryl C. Zeldin, MD, a Senior Investigator at NIEHS. "However, when we looked at where the health impact of the dust was the most significant, we found that the likelihood of having recent asthma symptoms was nearly three times greater among individuals with exposure to high levels of endotoxin in the bedroom."

The researchers found that all dust samples contained detectable levels of endotoxin. The average concentration of endotoxin ranged from 80.5 units per milligram of dust on kitchen floors to 18.7 on bedding. Family room floors had endotoxin concentrations of 63.9 units per milligram of dust; sofas had concentration levels at 44.8; and 35.3 units on bedroom floors.

"Interestingly, endotoxin exposure worsens asthma symptoms in adults, regardless of whether an individual has allergies or not" said Peter S. Thorne, Ph.D., a researcher at the University of Iowa and lead author on the paper. "This suggests that exposure to endotoxin increases asthma risk even in non-allergic individuals."

Since the mid 1960s, researchers knew that house dust contains endotoxin, but it is only within the last five years that they began to understand the impact of household endotoxin on human health. Knowing what triggers asthma, whether it is endotoxins or something else, may help a physician better prevent or treat symptoms.

"This study implies that it is not just the concentration of the endotoxin that matters," added Schwartz, director of NIEHS. "Understanding how factors such as duration of exposure, timing of the exposure, and genetic factors, contribute to the development of diseases like asthma will lead to new insights into how to prevent and treat this important disease." NIEHS is implementing new studies to better understand the role that the indoor environment plays in the development and severity of asthma.

NIEHS, a component of the National Institutes of Health, supports research to understand the effects of the environment on human health. For more information about asthma research, go to

This article originally appeared in the 09/01/2005 issue of Environmental Protection.

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