I think one of the most questions I was asked most often while working at the CDC was whether indoor air filters were effective at reducing symptoms of asthma and allergy.
This week the American Academy of Allergy, Asthma and Immunology has published a report on air filters and air cleaners that should help answer that question. The entire report is available free via PubMed.
Actually it goes well beyond that, with a thorough review of air filtration, the characteristics of airborne particulates – including allergens and particulate matter – and the range of available filter/cleaning strategies and technologies, from portable room air cleaners, to HVAC and powered electric filters.
One of the more interesting conclusions of the report is that air cleaning and filtration be viewed as a strategy for minimizing disease progression rather than as a treatment. As the report puts it, “It is not logical to expect that the observed disease state symptoms, often the result of previous prolonged exposures either in the home, other environments, or both, will abate within a few weeks or even months after the placement of an air-cleaning device or filter in the home environment. Other factors, especially source control and ventilation, might play a more important role than attempts to clean the air after the fact by means of filtration.”
They recommend that more rigorous and lengthy trials are needed before definitive recommendations on the efficacy of air filtration in improving disease can be made. Obviously there is a big role in these studies for more robust baseline and prospective data on symptoms and symptom severity, medication use and various objective markers (lung function). But I really like their idea of blinding and placebo-controlling the studies.
The group concludes that, given the current evidence, use of effective air filtration does reduce indoor levels of ambient particulates, that “that might trigger disease processes themselves.”
What to use? “Portable room air cleaners with HEPA filters, especially those that filter the breathing zone during sleep, appear to be beneficial. For the millions of households with forced air HVAC systems, regular maintenance schedules and the use of high-efficiency disposable filters appear to be the best choices.”