There is no definite evidence of filtration clinically benefiting patients with allergic disease, but this may be the result of the studies being of insufficient durations to prove benefit. The best review of the topic is by Sublett et al in 2010, a report of the Indoor Allergen Committee of the American Academy of Allergy Asthma and Immunology. This paper is well referenced and I do not think anything has changed since publication. One of the challenges is that the size of various allergens found inside vary, making the optimal filter possibly differing among allergens. HEPA filtration, devices that capture particles 0.3 micron and greater, are considered necessary for animal allergens and mold spores. Pollen is much more easily captured, although the possibility of pollen fragments could provide a source of pollen allergens in smaller particles.
In summary, the AAAAI does not recommend any specific method of in-room filtration for in-room or window air conditioners. The choice will depend on the type of allergy and a variety of features of the living space, which would make designating a specific device or filter type challenging. The following quote from the reference summarizes the state of the art:
“As far as optimal choice of cleaning devices, initial cost and ease of regular maintenance should be considered. 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. However, further studies and research in this area are desirable to make more definitive recommendations in the role of air filtration on improving disease outcomes.”
Sublett JL et al. Air filters and air cleaners: rostrum by the American academy of Allergy, Asthma & Immunology Indoor Allergen Committee. J Allergy Clin Immunol 2010;125:32-38.
I hope this information is of some assistance.
All my best.
Dennis K. Ledford, MD, FAAAAI