The promise of an air purifier is an enticing one: An appliance designed to cleanse the air in your home, getting rid of all the impurities including odors, smoke, dust, and pet dander. Given the fact that indoor air can have levels of certain pollutants up to five times higher than outdoor air, we get it. Some models may even be able to target bad air that creeps into your apartment or home, especially if you live in an area affected by pollution, or natural disaster.
Most people shouldn't be worried about exposure to temporary pollutants like smoke or exhaust in the air outside your home, as they dissipate over time, explains Ryan Roten, D.O., an emergency medicine doctor with Redlands Community Hospital in California. "In the short term, people will have asthma-like symptoms, primarily, or symptoms closer to allergies or sinusitis, including stuffy nose and a bit of a cough," says Dr. Doten, who has been treating patients with underlying respiratory illnesses as mass wildfires rage along the West Coast and air quality reaches new lows. "If the smoke is dense enough, you might have some headaches due to carbon dioxide, and those with issues like asthma or COPD will have it worse in the moment."
Air purifier can indeed neutralize some of the threat posed by air pollution and by indoor activities. In reality, though, not all air purifiers necessarily live up to their marketing hype.
How do air purifiers work?
Air purifiers usually consist of a filter, or multiple filters, and a fan that sucks in and circulates air. As air moves through the filter, pollutants and particles are captured and the clean air is pushed back out into the living space. Typically, filters are made of paper, fiber (often fiberglass), or mesh, and require regular replacement to maintain efficiency.
That means, in addition to the purchase price of an air purifier, you should also factor in operating costs and filter replacement costs. Operational costs can easily amount to $50 annually, since you should be running air purifiers near constantly to garner the benefits. Filter replacements can run upwards of $100 a year all told.
How frequently you will have to change filters varies based upon the purifier type and usage. Some filters are reusable and washable, but they require meticulous maintenance, so you don't usually find them on the most effective air purifiers. Reusable filters are generally better at removing larger particles from the air, like dust mites and pollen. You'll also find UV (ultraviolet light) filters on the market, which often claim to destroy biological impurities like mold or bacteria, but many require higher wattage and greater exposure to be effective (not to mention some bacteria is UV-resistant).
Other air purifiers use ionizers to help attract particles like static — negative ions bond to dust and allergens and make them settle out of the air. If you're interested in buying desktop air purifier that uses ionizers, make sure it does not produce ozone, a gas made up of three oxygen atoms that is often marketed as helping break down pollutants, because ozone could be a lung irritant and further aggravate asthma conditions. Usually the air purifiers with ozone will have that listed on packaging or in the marketing descriptions.
What are air purifiers supposed to filter out — and do they actually do it?
Most filters on the market are designed to capture particles like dust and pollen, but don’t catch gases like VOCs (volatile organic compounds) or radon. That would require an adsorbent, like activated carbon. In fact, the Environmental Protection Agency (EPA) warns that the functionality of air purifiers is limited in terms of filtering out gases, and that you must frequently replace filters for optimal functionality, usually about every three or so months.
Many air purifiers are good at filtering pollutant particles out of the air (dust, smoke, pollen, etc.), but they are not necessarily very good at removing gaseous pollutants like VOCs or radon from the air that may accumulate from adhesives, paints, or cleaning products. Allergens that are embedded into furniture or flooring are also not captured by them.
Additionally, the effectiveness of air purifiers in real-world situations likely won’t mimic those of controlled conditions in a lab (what those "99% effectiveness" claims are referring to!). The location, installation, flow rate, and how long it is operating for will all vary, as will the conditions in the space. In addition, there are other things happening in your home that may effect the efficacy like ventilation (open or closed windows), and new particles are constantly emerging, so the air may not as filtered as the claims may have you believe.