Effectiveness of Air Filters and Air Cleaners in Allergic Respiratory Diseases

Air filtration is frequently recommended as a component of environmental control measures for patients with allergic respiratory disease. Residential air filtration can be provided by whole house filtration via the home’s heating, ventilation, or air conditioning system, by portable room air cleaners, or a combination of the two. Appliances to filter the sleep breathing zone also have been developed. High-efficiency whole house filtration, high-efficiency particulate air sleep zone air filtration, and high-efficiency particulate air room air cleaners all appear to provide various degrees of benefit. Recent studies of various types of filtration, used alone or as part of more comprehensive environmental control measures, are reviewed.

Keywords: Air cleaner, Air filter, Air filtration, Breathing zone, CADR, Clean air delivery rate, Environmental control, Furnace filter, HEPA, HVAC, Indoor air, Indoor allergens, Intervention measures, Ozone, Particulate matter, PM, Room air cleaner, Sleep breathing zone, Ventilation, Whole house filtration

Environmental control practices (ECPs) are a group of measures recommended to reduce exposure to indoor allergens (eg, dust mites, household pets, cockroaches, mold, mice) or nonallergic triggers (eg, environmental tobacco smoke [ETS], wood smoke, volatile organic compounds, particulate matter [PM]) [1]. Historically, many of the common suggestions have been empiric and not based on scientific data or evidence-based clinical trials. As a better understanding of the impact of the characteristics of housing stock [2, 3] and occupants [4] on the indoor living environment has evolved, more effective measures have been identified. These may include modification of the occupant’s habits, remediation, and/or modification of the dwelling and its furnishings, structure, or ventilation, including the use of air filtration. One major drawback in many ECP studies has been the focus on a single allergen (eg, dust mites [5]) or intervention (eg, room air filtration for cat or dog allergy [6–8]). In fact, most allergic individuals have polysensitivity to multiple allergens. ECPs are therefore much more likely to be beneficial if targeted against triggers or allergens known to be problematic for the individual.

In the case of filtration, little attention has been paid to variations among the various appliances themselves, and no clinical comparisons have been done between the benefits of whole house filtration (WHF) versus those of portable room air cleaners (PRACs). According to the most recent American Housing Survey, 75% of US housing units have ducted forced air heat, while 63% have ducted central air conditioning [9]. When used in combination, these ducted heating systems are termed heating, ventilation, air conditioning (HVAC) systems. HVAC systems offer the opportunity for WHF, but poorly maintained or contaminated systems may actually increase the risk of asthma and other allergic respiratory symptoms [10]. Simple forgetfulness by the occupants in replacing the filter at suggested maintenance intervals may be the most common issue. HVAC service technicians frequently find round air filter that have not been changed for years when providing repair or maintenance services [11]. Dirty filters themselves can become a source for air contamination by allergens, particularly fungal spores [12], and can then be trapped, colonized, and released downstream as the overloaded filter fails [13]. Other issues, including air bypass from poor filter fit and duct leakage, may further confound the effectiveness of filtration in HVAC systems.