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“Air purifier” is a great name for a product: it’s simple, it’s direct and it addresses a major universal concern. It is as universal as it gets. After all, even little kids have been exposed to the idea that the air is not that clean anymore, that there is pollution and “bad things” in it. The first thing a person will associate with the term “air purifier” is “a device that will clean the air and get rid of bad things in it”.
What we need to know to evaluate the usefulness of air purifiers is:
- What are the “bad things” in the air and who they affect
- What air purifiers do (how they work)
- Who they benefit
The reason we need to evaluate them and the claims made by manufacturers is that their market is rising fast in an economy that is not growing that fast anymore.
The chief reasons listed by the market economy reports are:
- Rising awareness about the impact of indoor pollution
- Increased overall air pollution due to emission of harmful particulate matter
- Increased incidence of allergic respiratory disorders
- More stringent air quality regulation
- Higher quality and efficiency of HEPA filter based equipment
This is a bullet point summary of trends detailed in the reports. It is not hard to see that the reasons for this market growth are at the same time powerful driving forces and stable factors. Air pollution isn’t going anywhere soon, people are keeping pets indoors more than before and these factors will keep the morbidity (rate of illness in a given population) on the rise.
Simply put, an air purifier is a device (either stand-alone, transportable units or affixed to an “air handler unit”) that removes contaminants from the air in an enclosed environment. The most important technological breakthrough for their rise was the development of HEPA (High-efficiency particulate arrestance) filters in the 1950’s.
There is not much we can do about outdoor air pollution and as urbanization increased in the past 50 years, the absolute number of people exposed to air pollution increased. However, we have a problem there: official organisms and scientific information are conflicting concerning whether air pollution has been on the rise or declining (do not confuse this with global warming). The World Health Organization claims it is on the rise (WHO Global Urban Ambient Air Pollution Database -update 2016).
A detailed report by Ritchie and Roser (22) shows evidence it is declining. The Unites States Environmental Protection Agency (EPA) (15) points out that regulatory measures were adopted since the 1970s. Fenger (10), in a peer reviewed published article, claims that both the quality and the perception of pollution have changed during the past 50 years.
Whatever it is, some things are undisputable:
- The absolute and relative number of individuals exposed to indoor air pollution has increased for the simple reason that urbanization increased
- Pollution studies advanced and indoor air pollution causes for several diseases have been established
It is significant that the Indoor Air Quality Association (IAQA) was founded in 1995, creating a landmark in the evolution of these many factors (regulatory policy, actual indoor pollution increase, awareness and morbidity).
What Do Air Purifiers Actually Do?
Regardless of what kind of device it is, an air purifier will function by performing something on ambient air that is pumped into it and emitted from it after being processed. They may filter, burn, ionize, irradiate incoming air, hopefully making it particulate-free or cleaner in some way. These are the current methods used by manufacturers (3, 1):
- Thermodynamic sterilization (TSS)
- Ultraviolet germicidal irradiation – UVGI
- High-efficiency particulate arrestance (HEPA) filters
- high efficiency MERV 14 filter
- Activated carbon
- Polarized-media electronic air cleaners
- Photocatalytic oxidation (PCO)
- Ionizer purifiers
- Ozone generators
- Titanium dioxide (TiO2) technology
A summary of how each technology works was reviewed by Grabianowski (13).
Different air purifiers can make you happy or not, depending on what the consumer’s goal is: allergy control, asthma, cardiac conditions, odor control?
Depending on the technology used, air purifiers can perform one of the following:
- Filtration of particles. The notorious HEPA filters, which is the basis for many air purifiers, removes at least 99.97% of down to 0.3 micrometer particles. The filter needs replacement and in dusty environments, it can be interesting to have a pre-filter to remove coarser particles. They are excellent for allergy control, since much of what causes allergies is particulate matter, especially mold spores. But there is a catch there: the mold that produces the allergenic spores grows on cellulose. Therefore, cheaper quality air purifies, where the filters are made of cellulose (cardboard-like) can actually increase allergy-risk. The trick here is to make sure the HEPA filter is made from fiberglass or other synthetic material. Ionizer purifiers, immobilized cell technology, among others, claim to remove particles as well.
- Killing of germs (whatever microorganism ends up sucked into the device). Thermodynamic sterilization burns them and UV irradiation destroys their DNA. It’s hard to say when these will be critically important out of medical or biological research applications. Most indoor pollution hazards are caused by particles.
- Removing volatile organic compounds (VOC). Activated carbon and polarized-media devices claim to do that. Examples of VOCs are formaldehyde, benzene and methylene chloride. They are air borne in room temperature and can cause serious damage to the lungs, liver, kidney and nervous system.
Air purifiers can be beneficial to everything, literally constituting life-savers, or nothing at all. It all depends on two things: subjects’ health conditions and type of indoor air pollutant. Depending on the type of air pollutant, whether or not the subject has a previous health condition, the environment may be seriously harmful and an air purifier is needed.
There is even a term to designate environments where the air quality poses a health risk to anyone inside it: the sick building syndrome. The disorders are usually caused by the outgassing of some types of building materials, VOCs, molds, improper ventilation and filtration (16, 20, 18).
Individuals who are allergic or suffer from other respiratory illnesses may need an air purifier at least in the main room they occupy. But the range of disorders that indoor air pollution may cause is not restricted to these and more powerful (and expensive) purifiers may be needed to prevent health deterioration of those in the environment.
How Much Research Is There?
As for studies on the effectiveness of air purifiers themselves, they are recent and increasing. The first meta-analysis from 2005 did not provide conclusive results (14, Cochrane Foundation meta-analysis).
It should be noted that there is a high number of published articles from China, India and other developing countries where air pollution in general and indoor air pollution are associated to an alarming rise in respiratory disorders.
A Pubmed advanced search for the search terms “air + purifier” on the title and abstract resulted in 63 entries. The same search on Google Scholar since 2013 resulted in 1120 entries. Some studies are published in mainstream peer reviewed journals. It must be noted, however, that indoor air quality is a recent scientific concern and its outlets are equally recent.
Also, a main concern is that although air purifiers have been shown to be effective in preventing or improving health conditions associated with indoor air pollution, some scholars point out that the main health burden of air pollution, especially particulate matter pollution, is outdoor air pollution and refers to cardiovascular diseases (19).
Other studies claim that indoor air pollution is becoming even more relevant that outdoor air pollution, especially in relation to VOC (Wang et al 2007).
Fisk points out that reviews of research, at this point, are difficult given the disparity of methods and approaches. On average, the improvement of health outcomes is modest (11).
Do Air Purifiers Help?
Except for a meta-analysis from 2005 that couldn’t find conclusive results given the scarcity of studies and discrepancy of methods, most research points to some level of benefit in the use of air purifiers. Also, research shows it helps not only allergic or asthmatic patients, but anyone exposed to sufficiently hazardous indoor air pollution.
In a study involving 35 healthy college students in Shanghai, China, the group that remained 2 weeks in an air purified environment had remarkably reduced biomarkers of inflammation, coagulation, vasoconstriction, lung function, blood pressure and fraction exhaled nitrous oxide (7).
An important benefit of air purifiers refers to cardiovascular diseases. Particulate matter smaller than 2.5 micrometers is capable of triggering a chain of reactions (including oxidative stress, inflammation, autonomic imbalance, etc) that may lead to “vasoconstriction, endothelial dysfunction, increased blood pressure (BP) and heart rate, myocardial ischemia, impaired heart rate variability (HRV), repolarization abnormalities, arrhythmias, and enhanced thrombotic and coagulation potential.
Longer-term exposures have been linked to the chronic progression of atherosclerosis as well as the increased incidence of overt hypertension and diabetes mellitus” (19).
Are They Safe?
Some air purifiers produce ozone, which is an unstable tri-oxygen molecule that is highly effective in causing oxidative harm (killing microorganisms, but also harming our health). The United States Environmental Protection Agency as well as some of its State chapters, such as the California Environmental Protection Agency warn against these devices.
Except for those, and for the risk of fungus growth on cheap HEPA filters not substituted frequently, air purifiers are generally safe.
Several claims and recommendations may be concluded from the available epidemiologic and research data. The most important is that if you live in a highly polluted area, you probably want some protection when you are indoors. This was obvious by the amount of research and alarming claims coming from developing and rapidly industrializing countries.
If you are or have allergic or asthmatic people in your home or office, you probably need an air purifier.
But if you don’t live in a particularly polluted city or have any respiratory disorder, I didn’t find in research a strong reason for you to need an air purifier. Keeping the house clean, vacuuming carpets and dusting surfaces is usually sufficient.
The bottom line here is: watch out. The world is changing. Clean and nice neighborhoods can become polluted and dangerous very fast. Monitor pollution indicators and, if you are at risk, air purifiers can be one of the best solutions.
- “Residential Air Cleaners (Second Edition) – Indoor Air – US Environmental Protection Agency”. epa.gov.
- “US Air Purifier Market By Filter Type, By End User, Competition Forecast & Opportunities, 2011 – 2021”. TechSci Research report.
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- Boulanger, Guillaume, et al. “Socio-economic costs of indoor air pollution: A tentative estimation for some pollutants of health interest in France.” Environment International 104 (2017): 14-24.
- Breysse, Patrick N., et al. “Indoor air pollution and asthma in children.” Proceedings of the American Thoracic Society 7.2 (2010): 102-106.
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- Chen, Renjie, et al. “Cardiopulmonary benefits of reducing indoor particles of outdoor origin: a randomized, double-blind crossover trial of air purifiers.” Journal of the American College of Cardiology 65.21 (2015): 2279-2287.
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- Park, Hye-Kyung, et al. “Effectiveness of air purifier on health outcomes and indoor particles in homes of children with allergic diseases in Fresno, California: A pilot study.” Journal of Asthma 54.4 (2017): 341-346.
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