Air cleaners and air filters alone have not been shown to be clinically effective at reducing allergy symptoms.
Last Friday (March 31) I was very fortunate to be able to participate in a round table discussion on indoor air research. This meeting was conducted by university indoor air scientists and engineers and was attended by experts from industry (HVAC manufacturers, air filter manufacturers and filter media manufacturers), the academic community and the medical community. It was a lively and beneficial discussion.
At one point a practicing Allergist made the observation that he does not recommend ANY of the products produced by any of the manufacturers present. The reason is that he is just not convinced that there is good clinical evidence supporting the use of air filters, air purifiers or other air cleaning devices for health benefits.
Actually, he made a good point and he is right about there being no good studies linking the use of air cleaning devices alone and respiratory health improvements sufficient to reduce medicine usage. There is much more to the story which we will explain. However, this is a good point to remember when the next salesman or marketer tries to sell you that “cure-all” indoor air product. In fact, it is worth repeating. There is no good clinical evidence linking the use of air cleaning devices alone and health benefits. If someone tells you otherwise, run, don’t walk, for the exit.
So, what’s going on here? First, double-blind clinical trials are expensive. Air cleaning device manufacturers do not have the money to conduct these studies. So very few have been done.
Secondly, we know absolutely that good products like HEPA air purifiers will reduce particle counts and exposure to airborne allergens and irritants. (I have done these particle counts myself and can attest to reductions in particles in a room by up to 90%.) There have been some good studies done showing improved allergy symptoms in people with cat allergy who use a HEPA air purifier in their bedroom.
Thirdly, very few people are allergic to just one substance. Most people with allergies are allergic to dust mite proteins. Dust mites are found in beds, pillows, upholstered furniture and carpeting. Dust mite proteins (feces) are relatively big (over 10 microns) so they settle out of the air quickly. The chances of pulling dust mite feces from the air are very small. More importantly, no air cleaning device made can stop dust mite allergen from going from a pillow or bed to the breathing zone of the allergic person.
Therefore, it stands to reason that a comprehensive approach is the only one that will work – one that involves all aspects of indoor exposure to allergens. That is exactly why the Inner City Asthma Study is so exciting. We have covered this study before but it is worth mentioning again. This is a massive study done in seven cities in the United States covering over 900 children with allergy driven asthma. It is funded by the NIH and is well designed. The environmental controls consisted of covering the mattress and pillow with dust mite proof covers, using a HEPA air purifier in the bedroom, using a vacuum with a HEPA filter in the residence and pest extermination. And the results are remarkable. In fact, the improvement in symptoms of those asthmatic children is comparable to the use of inhaled corticosteroids. It is not only working. It is working more cost effectively than the most advanced medications – with no side-effects!
In a way I agree with my Allergist friend. If all you are going to do is buy a filter or some kind of air cleaning device, save your money. You would be far better off spending the money on pillow and mattress encasements. But if you are going to get serious, then a comprehensive program of environmental controls is the proven and tested way to go.